Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

Monica Francesca Blasi; Valentina Caserta; Chiara Bruno; Perla Salzeri; Agata Irene Di Paola; Alessandro Lucchetti

doi:10.1371/journal.pone.0250888

. 2021 Apr 29;16(4):e0250888. doi: 10.1371/journal.pone.0250888

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

Monica Francesca Blasi ^1,^*,^#, Valentina Caserta ^1,^#, Chiara Bruno ^1,^#, Perla Salzeri ^1,^#, Agata Irene Di Paola ^1,^#, Alessandro Lucchetti ²

Editor: Patrick J O Miller³

PMCID: PMC8084192 PMID: 33914839

Abstract

Illegal driftnetting causes each year several entanglements and deaths of sperm whales in different Mediterranean areas, primarily in the Tyrrhenian Sea. In summer 2020, during the June-July fishing season, two sperm whales were found entangled in illegal driftnets in the Aeolian Archipelago waters, Southern Italy. These two rare events were an exceptional chance to collect behavioural and acoustics data about entangled sperm whales. We analysed 1132 one-minute sets of breathing/behavioural data and 1575 minutes of acoustic recording, when the whales were found entangled, during the rescue operation, immediately after release, and in the days thereafter. The first whale was generally quiet showing a general status of debilitation/weakness, numerous skin lesions, and low breathing rate (0.31 (0.60)); it collaborated during rescue operations. On the contrary, the second whale showed a high level of agitation with a high breathing rate (1.48 (1.31)) during both the entanglement period and the net cutting operations, vigorously moving its fluke and pectoral fins, opening its mouth, sideway rolling or side fluking and frequently defecating. Acoustically, the first whale produced mainly single clicks in all phases except for two series of creaks during rescuing operations while the second whale produced a wide range of vocalizations (single clicks, likely either slow clicks or regular clicks, creaks, and codas). Our observations indicate that acoustics, respiratory and behavioural parameters may be useful to monitor the physical/physiological status of sperm whales during disentanglement operations.

Introduction

The sperm whale (Physeter macrocephalus) Mediterranean population, isolated from the Atlantic population as shown by genetic evidence [1, 2], is considered “Endangered” based on the most recent assessments [3, 4]. Indeed, the Mediterranean population is facing a drastic decline over the last half of this century, counting less than 2,500 mature individuals [4–6]. The main threat faced by this species is entanglement by large-scale driftnets fishery [7–9] classified as “a concerning matter” by the International Whales Commission (IWC) in 1994 [10]. Starting from the 1980s, driftnets have been used on large scale fisheries for decades by numerous fleets of the Mediterranean Sea to catch mainly large pelagic species, such as swordfish (Xiphias gladius) and blue tuna (Thunnus thynnus) [11–13]. Although driftnets in open waters have been banned by the United Nations since 1992 and the use of these nets of all sizes was prohibited by the European Union from 2002, the illegal use of driftnets continues to be reported in several Mediterranean areas such as Turkey, Algeria, Morocco, Spain, and Italy [6, 7, 9, 12, 14–16]. As a result, a dramatic increase in bycatch mortality of sperm whales in the Mediterranean Sea was observed in the period 1986–2000, from 20–30 estimated cases per year before 1990 to > 100 cases up to 2010 [17]. According to the Italian Database on Cetacean Strandings [18], from 2000 to 2020, 87 sperm whales stranding records have been registered with 105 animals involved. In the last two years, 17 of the 21 sperm whales stranded in Italy were found along the Tyrrhenian Sea coast. This part of the Mediterranean basin is thought to be an important feeding/breeding ground for this species, where both mature/immature males and social units of mature females with their juveniles/calves are regularly encountered [19–22] as a result of the morphological aspects of the bathy-morphological setting, characterized by canyons and seamounts, which have already been positively related to the presence and distribution of the sperm whales [23, 24]. The Aeolian Archipelago located in the Southern Tyrrhenian Sea (Sicily, Italy) is no exception [25]. Several sperm whale encounters (both solitary individuals and social groups) have been documented in this area in the last six years [26]. Moreover, two juvenile male sperm whales were reported to be entangled in illegal driftnets from 2007–2017, and successively stranded dead along the nearest coast as part of the net had not been removed.

Other studies have already described the lethal consequences of entangling large whales in nets along the coast of Ecuador [27, 28], in Southern Brazil [29], and in the Mediterranean Sea [11, 17]. However, behavioural observation and vocalizations of a social unit of sperm whales entangled in illegal driftnets have been previously documented only in the Southern Tyrrhenian Sea [11], but the acoustic analysis was conducted on a social unit as sounds could not be ascribed to individual whales.

In this study, we documented two sperm whales’ entanglement events that occurred in the Aeolian Archipelago, during summer 2020. Data on the behaviour, breathing pattern, diving time, and acoustic production of these entangled whales were collected in different phases, from entanglement to post-release.

Materials and methods

On 26th June 2020 at 10:01 (all the times are in 24h format and related to UTC+1 time zone), a severely debilitated 10 m juvenile male sperm whale (named “first whale”) was found entangled by the tail in a driftnet, 6 miles northern of Lipari island (Aeolian Archipelago; Fig 1).

Fig 1 — Initial (black symbols) and final positions (white symbols) of first (triangle) and second (circle) whales.

It had several abrasions and scars all over the body, especially in the dorsal area. No signs of starvation were observed.

On 18th July 2020 at 11:43, another juvenile sperm whale of 9 m (named “second whale”) was found completely entangled in a driftnet five miles north of Salina (Aeolian Archipelago; Fig 1). Sex was not identified, as the animal was generally very active and nervous not allowing to researchers to retrieve any clear footage of the ventral area. Sign of starvation or severe injuries were not observed.

Behavioural, breathing pattern, and acoustics data were collected throughout the entire duration of the disentanglement process, which has been divided into phases, in order to associate data with the related events. Due to the different approaches adopted by the rescuers and the consequent outputs, some phases were in common between the two whales, while others were specific for a single whale. The common phases were described as follow: a) “trapped”, including the finding of the entangled animal and waiting for the Italian Coast Guard intervention; b) “rescuing”, involving the disentanglement process performed by the scuba rescuers. On the other hand, phases specific to the first whale were: a) “pre-rescue”, including the Italian Coast Guard arrival, assessing the situation and pre-disentanglement operations (i.e. immobilizing the tail with a rope and secure it to the main vessel); and b) “post-rescue”, involving monitoring after the release (Fig 2).

Fig 2 — A) Trapped (only tail). B) Pre-rescue. C) Rescuing. D) Post-rescue.

For the second whale, one specific phase was observed, which was described as “following”, in which operators followed with the boat the escaping whale. This phase included a night chasing and no data were collected (Fig 3).

Fig 3 — A) Trapped (all body). B) Rescuing. C) Rescuing (first day) (first attempt of net removal using a boat hook). D) Rescuing (first day) (second attempt of net removal using a boat hook). E) Following.

Finally, a “follow-up” monitoring was performed aimed to re-sight the whales.

The behavioural displays of the entangled individuals were recorded using a combination of focal observations (sampling at one-minute intervals) and video recording [30]. Underwater cameras (GoPro Hero7) were used to record the sperm whales’ behaviour during the disentanglement process [30–32]. The behaviour of the sperm whales was recorded according to different behavioural activities previously reported in literature [11, 33–35], i.e., open mouthed, side roll, agitation of fluke and pectoral fins, side fluke, lobtail, spy hop, and defecation. The rate of each behavioural activity (number of records/number of one-minute behavioural sets) was calculated in the different phases for both whales.

The breathing pattern was recorded at one-minute intervals and the mean (SD) breaths per minute (breathing rate) was calculated for each phase. Since the assumption of the homogeneity of variance was rejected, non-parametric Kruskal-Wallis tests and post-hoc testing using un-paired Mann-Whitney U tests with a Bonferroni-adjusted alpha level were used for comparisons of median values in breathing datasets among different phases and between whales. Although both whales displayed surface behaviour, the second whale performed several dives, the dive time of which was recorded [30, 36, 37].

Acoustics offers important insights into the behaviour of sperm whales, providing useful information for rescuing operations [38–42]. The sperm whale vocalizations were recorded using a hydrophone (Aquarian Audio H2a, sensitivity -180 dB re: 1 V/μPa) deployed by the research boat and connected to a wideband solid-state recorder (sampling rate: 48 KHz) at a depth of about 5 m. Differently to behavioural data, acoustics recordings were not constant, because the hydrophone was deployed only in optimal conditions (i.e. minimal background noise due to rescue operations). Emissions were classified into three categories: “single clicks” (SC); “creaks” (CR) and “codas” (CO), according to the click structure described in the literature [43–49]. The acoustical analysis was performed by Raven Lite 2.0.1 software, which has been used to measure upper and lower frequency limits and calculated inter-click intervals (ICI) for each detected sound. In addition, creaks and codas, which are composed by trains of clicks (ICI < 0.3 s), duration of the trains and time interval between trains have been calculated. In this study, “single clicks” were scored for sequences of clicks (ICI > 1 s) that were not organized in a defined structure, as described for “usual clicks” [39]. Kruskal-Wallis tests and Mann-Whitney U tests with post hoc Bonferroni correction were run to single out significant differences in ICIs (for single clicks and creaks) and duration (for creaks only) between whales and among the different phases.

All statistical analyses were performed with R 4.03.

Results

Entanglement events and rescue operations

The first sperm whale was found on the sea surface with its tail entangled and immobilised by the driftnet on 26^th June 2020 (Fig 2). For a short period, three other sperm whales were spotted about two miles away from the entangled animal, but no vocalizations were detected. At 12:24, two operators of the Coast Guard started pre-rescue operations to secure the whale’s flukes to the main vessel (Fig 2). In particular, the whale was cautiously secured to the main vessel with a rope performing a twisted-pair knot around the caudal peduncle. Rescue operations (disentangling the netting from the tail and cutting the netting twines without hurting the animal, when necessary) started at 14:20 with three divers of a local diving team. The whale remained moderately calm throughout all the rescue procedures and in about 55 minutes it was completely free to move. Subsequently, it stayed close to the divers who frequently touched its body in order to cut the remaining pieces of netting. After release, the animal was closely monitored for two hours, before disappearing (final recorded location is shown in Fig 1). On 29^th June 2020, three days after the first sighting, the entire whales’ group of four individuals was re-sighted and the whale was observed surfacing and diving regularly (data not shown).

The second sperm whale was found completely entangled and wrapped in the driftnet on 18^th July 2020 (Fig 3). No other individuals were sighted or acoustically detected in the proximity of the animal. The rescue operations started at 12:40 and in an hour a Coast Guard diver removed most of the net from the body except for the tail. Then, a second rescue diver attempted to secure the tail to the main vessel, a procedure recommended for small cetaceans by Hamer and Minton [50]. Meanwhile, eight other vessels arrived in close proximity to the animal, but only two of them were rescue boats, which brought seven more divers to support the rescuing operations. The animal got nervous and started to move away from the area breaking the rope connected to the main vessel. Two attempts were made to reach the net using boat hooks, but they got stuck in the tangle of netting. Monitoring activities were performed overnight in order to constantly follow the animal and a lit mark buoy was fixed to the tail. The next morning three more attempts were made by another group of divers, for a total of five boats and ten divers, although the sperm whale started to perform long dives. Therefore, it was difficult to follow its route, so that the whale was last tracked by its blow at 14:38. At 20:00, rescue operations were suspended and scheduled to resume the next day in daylight. In the following days, Coast Guard searched the animal in the area around the last known location, but no results were provided. On 5^th October 2020, seventy-nine days after the first sighting, the whale was re-sighted at 17:30, still entangled, at 1 mile from Salina (the same Island where the whale was first spotted) and, as it was very elusive, no rescue operation could be started. Nevertheless, the whale was acoustically monitored for 13 hours during the night.

Behavioural data

A total of 1,132 one-minute behavioural sets were analysed, 298 for the first whale (26^th June 2020) and 834 for the second whale (18^th-19^th July 2020). The rate of each behavioural activity at each phase was reported for both whales (Fig 4).

Fig 4 — A) First whale. B) Second whale.

The first whale was generally quiet and poorly reactive during entanglement and rescue operations. General status of debilitation and weakness was observed with numerous lesions and wounds on its body and flukes; the whale appeared not to react nervously to the rescue operations, apart from two behavioural categories. i.e., opening of mouth and slight agitation of fluke and pectoral fins (Fig 4A). Defecation was observed only in the post-rescue phase (Fig 4A). On the contrary, the second whale was particularly agitated during both the entanglement period and the rescue operations, vigorously moving its fluke and pectoral fins, frequently opening its mouth, and sideway rolling or side fluking and defecating (Fig 4B). Although the remained attached net, during the following period, the whale was observed lifting the fluke out of the water to bring it down onto the surface of the water in order to make a loud slap (lobtailing). Spy-hopping, breaching, and fluke up were never recorded for both whales after release and throughout the following period.

Breathing pattern and diving time

The dataset, as for the behaviour, included 1,132 one-minute breaths sets, of which 298 for the first whale and 834 for the second whale. The breathing rate (number of breaths per minute bin) was calculated over different phases showing a different trend for the two whales (Fig 5).

Fig 5 — A) First whale during all phases on 26/06/2020. B) Second whale during the first day (trapped, rescuing and following on 18/07/2020). C) Second whale, second day (rescuing and following on 19/07/2020). SC = single clicks; CC = creaks; CO = codas. Dives are indicated as D followed by a sequential number.

Generally, the mean breath per minute bin was significantly higher for the second whale (N = 834) (up to 7 breaths per minute bin) than for the first whale (N = 298) (less than 4 breaths per minute bin) (Mann-Whitney U test: z = 15.0, P = 0.0001). However, significant differences were found among phases for the first (Kruskal-Wallis test: H_c = 28.5, df = 5, P = 0.0008) and second whales (Kruskal-Wallis test: H_c = 24.3, df = 4, P < 0.0001) (Fig 6). Particularly, higher breathing rates were found during rescuing operations for the first whale (Mann-Whitney U test, Bonferroni corrected alpha: P = 0.001) and during entanglement for the second whale (Mann-Whitney U test, Bonferroni corrected alpha: P = 0.001) (Fig 6).

Fig 6 — First whale (black) and second whale (white).

During the “trapped” phase the mean time between two breaths was 6.60 (2.50) minutes, ranging from 2–15 minutes, for the first whale, and it was 2.61 (1.26) minutes, ranging from 1–5 minutes, for the second whale. The first whale never dove during any phase while the average dive time was 13.07 (0.10) minutes for the second whale (calculated over 15 dives) (Fig 7).

D10 was the longest dive performed just before the second attempt of rescuing the second whale. Prior to this long dive, the whale regularly performed other shorter dives (Fig 7). D14 and D15 was the longest dives performed after several rescuing attempts (Fig 7).

Acoustic behaviour

A total of 34 minutes for the first whale, recorded in three phases (trapped, rescuing, and post-rescue; 26th June), and 22 minutes for the second whale, recorded during rescuing operations (18th July) were analysed. The sequence of vocalizations produced during surface behaviour significantly differed between the two whales. Particularly, the first whale produced primarily single clicks in all phases except for two series of creaks while the rescue operations were underway (Table 1).

Table 1. Each sound emission type temporal and physical parameters.

SINGLE CLICKS
	Phase	Clicks (N)	ICI (s)		Frequency limits (Hz)
First whale	Total	612	2.86 (3.99)		1087 (663)-20629 (3454)
	Trapped	322	3.39 (4.89)		1645 (92)-23877 (214)
	Rescuing	209	2.00 (2.51)		426 (439)-17004 (979)
	Post-rescue	81	2.84 (2.17)		577 (430)-17170 (460)
Second whale	Rescuing	12	4.91 (1.27)		1238 (352)-16441 (1107)
CREAKS
	Series	Trains (N)	Train duration (s)	Time interval (s)	Frequency limits (Hz)
First whale	1	5	0.557 (0.277)	0.90 (0.58)	1268 (55)-19964 (75)
First whale	2	1	0.651 (0.000)	*	66 (0)-16306 (0)
Second whale	1	43	0.860 (0.218)	2.43 (2.95)	1800 (42)-14653 (4320)
Second whale	2	14	0.746 (0.175)	1.74 (0.91)	1766 (40)-16819 (1166)
CODAS (second whale)
Series	Type	Codas (N)	Coda duration (s)	Time interval (s)	Frequency limits (Hz)
Coda 1	Total	53	0.488 (0.025)	5.06 (2.61)	1714 (216)-16538 (1334)
Coda 1_3		21	0.492 (0.026)	*	1753 (203)-16669 (1687)
Coda 1_4		31	0.485 (0.025)	*	1687 (228)-16444 (1079)
Coda 1_5		1	0.492 (0.000)	*	1716 (0)-16703 (0)
Coda 2	Total	10	0.462 (0.033)	6.46 (2.94)	1306 (61)-16755 (1031)
Coda 2_3		3	0.476 (0.030)	*	1313 (69)-17281 (1018)
Coda 2_4		7	0.455 (0.034)	*	1303 (62)-16530 (1025)

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Quantity, duration (only for creaks and codas), time interval, and frequency lower and upper limits of each vocalization recorded. Mean (SD) values are reported for all data (Total) and each phase with acoustic data (Trapped, Rescuing and Post-rescue), series (1 and 2) and coda type (with 3, 4 and 5 clicks).

The second whale (acoustically recorded only throughout rescue operations), after a first series of creaks (named “creaks 1”), produced few single clicks followed by the first series of codas (named “coda 1”). (Table 1). Then, the second whale started a second series of creaks (named “creaks” 2) followed by a second series of codas (named “coda 2”), composed of just coda_3 and coda_4 (Table 1). The structures of these codas were: 2+1 (coda_3), 1+2+1 (coda_4) and 2+2+1 (coda_5) similar to the ones recorded among the Mediterranean sperm whale population [11, 48].

Additional 1519 minutes (from 19:04 to 06:15) of acoustic recordings collected during the second whale’s re-sighting on 5^th October were analysed separately showing a completely different pattern, i.e., several series of single clicks with ICI from 0.8–1.8 s combined with extensive pauses in click emission (silence periods) [51].

Single clicks

For the first whale 612 single clicks were recorded; the lower frequency limit of these clicks ranged between 66.0 Hz and 1885 Hz, while the upper frequency limit ranged from 14.85 kHz to 24.00 kHz. An average click rate of 0.43 clicks per minute was recorded, but the click rate was higher during rescuing operations (0.52) than trapped (0.29) or post-release (0.29) phases. On the contrary, only 12 single clicks were recorded from the second whale during the first day with the lower frequency limit of these clicks ranging between 207.4 Hz and 1653 Hz, while the upper frequency limit ranged from 13.76 kHz to 17.76 kHz. The mean ICI and frequency of single clicks were calculated for each whale (Table 1). For the first whale the mean ICI significantly differed among phases (Kruskal-Wallis test: N = 618, H_c = 65.6, df = 3, P < 0.0001) with higher values during entanglement (N = 322) than in the other phases (N = 296) (Bonferroni corrected alpha: P < 0.0001). However, during rescuing the ICI value resulted significantly higher (more than twice) in the second whale (N = 12) than in the first whale (N = 209) (Mann-Whitney U test: z = 5.9, P < 0.001) (Table 1).

The acoustic dataset collected during second whale re-sight included in total 12 series of single clicks (mean duration (SD): 11.61 (6.79) minutes) with a mean ICI (SD) of 0.91 (0.37) minutes combined with extensive pauses in click emission (silence periods) (mean duration of silence periods (SD): 52.87 (22.16) minutes). The click rate was constant, ranging between 0.55 and 1.25. Creaks and codas were not recorded in this period.

Creaks

A total of 63 creaks were recorded, among the two events. As it concerns the first whale, a first series of creaks (creak 1) included five trains and 77 clicks in total, while the second series (creak 2) included only one train composed of a sequence of 10 clicks (Table 1). The numbers of clicks in creaks ranged from 4–23 with a mean value (SD) of 14.5 (8.1) clicks per train and 50% of the values are included within the range of 20–23 clicks per train. As it concerns the second whale, the first series of creaks (creak 1) was composed of 43 click trains of 942 clicks in total. The number of clicks in each train ranged from 7 to 37 clicks with the majority of trains (80%) within the range of 19–24 clicks, with a mean number (SD) of 21.9 (6.0) clicks per train. Then the second series of creaks (creak 2) included 14 trains of 306 clicks in total. The number of clicks in each train ranged from 16–32 with 70% within the range of 21–23 clicks and a mean (SD) of 21.9 (4.1) clicks per train.

The mean duration (s) of trains in each series of creaks and the time interval between trains (s) of each series for both whales are reported in Table 1, showing significantly higher train duration (Mann-Whitney U test: z = 14.1, P < 0.0001) and interval (Mann-Whitney U test: z = 7.0, P < 0.0001) in the second whale (N = 57) than in the first one (N = 6). A detailed analysis of each series of creaks was performed (Fig 8) showing significant difference between series for the first whale (Mann-Whitney U test: N₁ = 77, N₂ = 10, z = 4.5, P = 0.0001) but not for the second whale (Mann-Whitney U test: N₁ = 942, N₂ = 306, z = 2.4, P = 0.02).

Although several factors might have influenced whales’ acoustics emissions (i.e. timing at which whales had been entangled, number of boats present in the area, physical status, natural inter-individual variability, etc.), it is noted that creaks occurred only during the “rescuing” phase when the whales showed different behavioural displays related to stressful and traumatic conditions. In particular, for the first whale the first series of creaks was recorded at the beginning of rescuing operations, while the second series when half of the net was removed from its tail. Vigorous fluke movements and mouth opening were associated with creaks. For the second whale both creaks series were heard during the first day when several people (rescue divers and filmmakers) swam in the proximity of the animal; moreover, on the first day, the rescue team tried more times to remove the net with boat hooks, which got entangled in the netting. Agitation of fluke and pectoral fins, frequently opening the mouth and sideway rolling, and side fluking was also observed in association with creaks.

Codas

Codas were recorded for the second whale only. In total, sixty-three codas were detected, distributed in two different sequences (coda 1 and coda 2) (Table 1). A mean coda occurrence rate of 0.18 codas per second was recorded, but the coda 2 mean rate was slightly lower (0.16 codas per second) than coda 1 (0.19 codas per second). The inter-coda interval ranged from 2.8 to 21.6 s. The duration of codas ranged from 412-561 ms but 85% lasted between 440 and 500 ms with a mean duration of 484 (28) ms. Three coda types, containing 3, 4, and 5 clicks, were found and classified in accordance with Weilgart and Whitehead [52] (Fig 9).

Fig 9 — A) coda_3 (3-clicks). B) coda_4 (4-clicks). C) coda_5 (5-clicks). ICI_1 = ICI between the first and the second click; ICI_2 = ICI between the second and the third click; ICI_3 = ICI between the third and the fourth click; ICI_4 = ICI between the fourth and the fifth click.

Among all codas, 3-click codas (38% of codas; type 2+1) and 4-click codas (60% of codas; type 1+2+1) were found to be the most common, with the exception of a single coda formed by 5-clicks (type 1+2+2) occurred just once, while operators tried to disentangle the net using the first boat hook. A detailed analysis within codas pattern showed great variability in ICI duration, ranging between 2–300 ms (Fig 9). The two series of codas were mainly heard during the first day, when the whale, once the first part of the net was removed, started to move away from the rescue team, showing an active behaviour, vigorously moving its fluke and pectoral fins, frequently opening its mouth and sideway rolling or side fluking and defecating.

Discussion

This study provides new data on behavioural pattern, including acoustic behaviour, displayed by sperm whales under particularly stressful conditions (i.e. entangled in illegal driftnet targeting large pelagic species [53–57]) and compared these resulting observations to the existing literature about the acoustic behaviour of sperm whales in natural conditions [39, 40] and under similar or other (i.e. human-made noise) stressful contexts [11, 41]. Combining behavioural, respiratory, and acoustic data allowed us to gain a wider understanding on how sperm whales may react to entanglement and, consequently, to better manage rescuing operations, in order to reduce additional stress or accidental injuries to the animal.

Despite similarities between the two situations, two different reactions were documented. The disentanglement operations on the first whale lasted less than an hour and successfully freed the animal. On the other hand, the driftnet was completely removed from the body of the second whale, but not from the tail. The animal got nervous and started to swim away from the rescuers, who continued to search for it the next day, even after its disappearance. The different whales’ responses may be related to several factors, such as the individual’s behaviour, its health status, and the specific reaction to disentangling operations and to the rescue operations themselves (different number of vessels and operators in the rescue area).

The behavioural displays observed in this study have been previously reported in other cetacean species, primarily during aggressive/agonistic attacks or in stressful circumstances [58]. Our data are not enough to confirm such behaviours, which could be stereotyped postures of the species [59, 60] or behavioural modes adopted during particularly stressful conditions expressed in the proximity of an imminent danger [11]. Moreover, it is not excluded that these behaviours may be accentuated during traumatic events, occurring more frequently in stressful circumstances than under normal conditions [11]. In this study, only the second whale showed sideway rolling and side fluking, both behavioural displays which require a greater energy demand for a whale under traumatic conditions. This leads to the hypothesis that the entanglement of this whale may be recent compared to the first whale, which was found generally in poor health condition.

Our data suggest that the breathing pattern may be a good indicator of stress during entanglement events. The first whale showed significantly higher breathing rates during rescuing operations than in the other phases. Moreover, the second whale showed higher breathing rates than the first one. Considering the massive human presence around the second whale, this is consistent with the hypothesis that external disturbances may cause additional stress to the animal. Particularly, frequent and extended breaths at the surface are indicators of proximity with an upcoming dive, as these breaths enhance the diving time and the opportunity to execute longer dives in depth [61, 62]. On the contrary, when the breathing rate is less frequent, the dive is likely to have ended and the whale is resting and preparing for the next dive [63]. The duration of dive is known to be partially physiologically limited, but in most cases, it is under behavioural control [64, 65]. Ventilation is the result of respiratory frequency and tidal volume, and both parameters usually increase with the longer dive durations [66]. This type of respiratory alteration observed as increased ventilation has been reported for a variety of mammals [67, 68] and cetaceans [69], but never for rescuing operations of entangled sperm whales. Increased ventilation is necessary because of the oxygen deficit and accumulation of carbon dioxide acquired during submergence [70]. The rapid replacement of oxygen stores throughout the body is further facilitated by an increased heart rate during these surface intervals [71, 72]. The dive duration trend of second whale suggests that an increased ventilation might restore the high diving costs of the residual embedded net [73].

In this study, the acoustic pattern was analysed according to other studies on marine mammals [34, 74–78]. Although the entanglement conditions were similar, the two whales presented a different acoustic pattern. The first whale produced primarily single clicks (99.0%) in all phases except for two series of creaks (creak 1: 0.8%, creak 2: 0.2%) when rescue operations were in progress. The second whale after the first series of creaks (32.6%) produced few clicks (9.1%) followed by a first series of codas (40.2%) and a second series of creaks (10.6%) and codas (7.6%).

Particularly, in this study, the term ‘single clicks’ is used to indicate those sounds which resembled regular echolocation clicks (“usual clicks”) associated primarily with an echolocation-based foraging [79] but with some substantial differences. Firstly, click analysis shows a high average ICI (2.86 and 4.91s for first and second whales, respectively), consequently average click rates were very low (0.4 and 0.2 sec^-1 for first and second whales, respectively) in comparison with typical echolocation clicks used by whales in search of food [51, 79]. Jaquet et al. [38] described “surface clicks” as “vocalizations had a long inter-click interval (5 to 7 s on average, also called ‘slow clicks’) and sounded very metallic” (“clangs” according to Gordon [80]). Although the situation described in this study was atypical, plausible hypotheses might be that these clicks were used to echolocate the position of the rescuers [46], or also to keep contact with nearby whales [81]. However, for the second whale, the clicks emitted at the surface, did not fit perfectly with the description of “surface clicks” [38]. Commonly, “usual clicks” are usually produced in prolonged bouts interspersed with buzzes [79], which is true for the first whale (it constantly emitted clicks with slight fluctuations of the inter-click interval in accordance with the activity level, Table 1), but it is not clear for the second whale, which emitted just a 12-click train at a very slow rate between a long creak sequence and coda sequence, both triggered during high activity situations. Previous studies have shown that the click rate can be subjected to variations related to activity, group size, and physical condition [38, 44, 46]. The low click rates recorded for the first whale could be ascribed to a general state of weakness, due to the excessive suffering condition caused by the entanglement. Accordingly, when the second whale has been re-sighted, the acoustic recording included only usual foraging clicks (click rate: 50.3 (17.6) min^-1, N = 96; ICI range 0.86–1.83s, mean ICI: 0.91 (0.37) s), which are typically interspersed with periods of silence (~52 min average) [34], indicating its ability to dive (at which depth is unknown) and likely to forage, despite the residual net wrapped on the tail. A comparison with behavioural and breathing pattern data of this encounter was not performed because the whale was encountered just before sunset.

Creaks are a wide kind of vocalizations that include two main categories: long and short-lasting creaks [34, 45]. The first type is mainly associated with deep dives echolocation, especially in prey detection and targeting [34, 38, 45, 79, 80, 82–85]; while the second type includes “coda-creaks”, “chirrups” or “rapid-click” [47, 80] and is emitted in a social context for scanning other whales while lying at the surface [34]. In this study, creaks were recorded for both whales and shared similar acoustics parameters, of which some were consistent with previous literature. The ICI values, for instance, ranged between 5–100 ms like reported by Pace et al. [11] for whales in entanglement conditions. Additionally, the structure and the number of clicks contained in trains (range 10–37 clicks) is consistent with Goold’s “chirrups” (range 10–50 clicks) [47]. On the other hand, others vocalization characteristics were definitely different, such as duration (range 0.7–139 s) and click rates (21.4 sec^-1 for the first whale and 30.9 sec^-1 for the second whale), showing lower values than usual social creaks [47]. Despite those creaks had different occurrence rates (first whale: 1% of the total analysed emissions (N = 618); second whale: 43% of the total analysed emissions (N = 132)), those sounds were emitted only during the “rescuing” phase. In particular, when rescuers were operating around the whale by cutting or pulling the net off, suggesting that those sounds might be related to an extreme uneasiness. Furthermore, those sounds were associated with high breathing rates and distress-related behavioural displays. In nature, several animals emit sounds in the proximity of imminent danger or during traumatic events and stressful circumstances [86], like trapping [87–90], or, as observed in bottlenose dolphins (Tursiops truncatus) to elicit aid from another animal by emitting repetitive whistle sequences [91]. Another study [92] on bottlenose dolphins shows that the occurrence of whistle production was positively correlated with the occurrence of the supporting behaviours which the injured dolphins received from other individuals. Finally, Tellechea et al. [93] reported the sound behaviour of a stranded humpback whale (Megaptera novaeangliae) which emitted atypical “grunts”, normally associated with foraging, with a duration similar to the creaks found in this study (duration range 0.56–0.86s). Our data are not sufficient to assume the true function of these sound emissions although it is not excluded that their ICI and duration values could be related to the physical/psychological status of the animal or also a natural-intra-individual variability.

Codas are known to be involved in communication between sperm whales [34], and different coda repertoires may occur among populations (“vocal clans”) [94, 95]. The codas repertoire found in this study showed some similarities, mainly in its structure and duration with codas reported in other studies [48, 96–99]. Analogously to that reported in the Mediterranean Sea [48], the 3-clicks coda type (2+1) (38.1%) has been found, fitting in the description of a typical “2+1” coda family [11], with a coda-inner click interval ranging from 0.15 to 0.28 s. The occurrence of (2+1)-click type has been also described off the Balearic Islands [97] and in the Tyrrhenian Sea [96], even though it is believed to be more common among socializing whales than in solitary individuals [11]. Besides, this coda type was already found in whales in stressful conditions [11]. However, the recorded repertoire was dominated by a 4-clicks (1+2+1) coda type (60.3%), already reported in the Mediterranean Sea [11, 48, 99]. A single coda train of 5-click (1+2+2) has been also detected, previously documented only once for a group of sperm whales (group size > 3) in Greece (Aegean Sea) [48, 94, 100]. Finally, coda durations (0.4–0.5 s; overall mean duration 470 ms) were also similar to those reported in socializing whales off the Tyrrhenian Sea (range 0.4–1.2 s; overall mean duration 908 ms) or for entangled whales (range 0.2–5 s; overall mean duration 398 ms). On the other hand, the most important difference found in this coda repertoire is the values of the ICI within codas, especially for 4-clicks and 5-clicks types, which were more similar to creaks’ (ICI < 0.1 s) than Mediterranean socializing and entangled whales’ codas (ICI: 0.1–0.5 s). It is not excluded that the observed ICI differences may be related to the low coda sample collected in this study, but the co-occurrence of a short creak train between codas and the absence of other whales nearby, suggest that those vocalizations may be emitted for a different purpose than socializing. Among the probable hypothesis about the behavioural significance of these codas, the more reliable can be found in a particular category of codas, called “alarm codas”, reported by several authors [41, 101]. It has been observed that those vocalizations occurred when solitary whales or non-socializing groups are distressed by human or predator (killer whale, Orcinus orca)’ presence, and in association with altered surface behaviour. Accordingly, our codas have been produced by a non-socializing whale in a situation of disturbance and imminent danger, together with atypical surface behavioural displays (“opening of mouth”, “agitation of fluke and pectoral fins”, “sideway rolling”, “side fluking” and “defecating”). However, only few data were analysed and this hypothetical association between behaviour and acoustics needs further data and observations to be confirmed.

Recommendations

Past experiences with entangled cetaceans have shown that a clear and comprehensive set of guidelines should be followed to decrease the risk of mortality and/or further injury or stress, thus increasing the probabilities of post-release survival [50]. Experience gained from the present study shows that a high level of competence and preparedness, which includes being prepared with the right equipment, has a significant positive impact on successful disentanglement operations [50]. Before starting the rescue operations, a preliminary assessment of the general condition of the animal is recommended, to identify priorities and define appropriate and timely responses, and therefore desirable results [50]. Furthermore, it is essential to minimize the possible stress caused by the presence of boats and/or operators not involved in the disentanglement process [50]. However, psychological and physical stress in entangled whales is a key issue to keep under control, to minimize unexpected reactions during rescue operations, that could pose a risk to both whale (who may accidentally get injured) and operators (whose safety could be put at risk by sudden movements of a large animal). But this level of stress is difficult to detect and measure, even if it should be treated, reducing it wherever possible. In this paper behavioural, breathing and acoustic recording has proven to be a useful tool and a non-invasive way to continuously monitor the physical and psychological condition of entangled sperm whales, suggesting that these data should always be collected to continuously monitor whale status during the rescue operations.

Acknowledgments

We thank all people and organizations who collaborated on this work. Francesco Principale and the Coast Guard of Lipari, Catania, Messina, Milazzo, and Napoli for the incredible effort in these two entanglement cases to save the two individuals of sperm whales. Moreover, we thank Lipari Diving and Muciara Diving for the collaboration in rescuing operations. Dr. Clara Monaco for reporting us the second whale entanglement. We also thanks Sea Shepherd Italy for the logistic support during the night monitoring sessions. Last but not least, we thank the volunteers and students of Filicudi WildLife Conservation who assisted during the monitoring sessions supporting the team in the collection of data. This work is part of the activities of a European Life Project named Life Delfi aimed to reduce negative interactions between fisheries and cetaceans in different Mediterranean areas. No invasive methods have been used in this study; hence no ethics statement is required.

Data Availability

All relevant data are within the manuscript.

Funding Statement

The author(s) received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0250888.r001

Decision Letter 0

Patrick J O Miller

12 Feb 2021

PONE-D-20-40631

Behaviour and acoustic vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

PLOS ONE

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Reviewer #1: Review PlosOne D-20-40631

This paper presents an interesting description of two net entangling events that occurred to sperm whales around the Aeolian Islands in the lower Tyrrhenian Sea. The authors describe the disentangling operations and the associated behaviour of the two animals during the rescue operation. The paper is pretty descriptive, and scientific results are limited to a description of occurred behaviours, rather than a scientific interpretation; however, the paper depicts the problem of illegal drifnets and gives cues and recommendations about how to face such entangling events and related rescue operations. Considering this, I recommend the publication with a minor revision to correct some inconsistencies and ambiguities in the acoustic behaviour description. Overall, it is a very interesting lecture on an unusual and poorly known event.

124: please add more information on recording: depth of the hydrophone ? sampling rate of the recorder ?

127: measure rather than “extrapolate”

127: frequency parameters rather than just “frequency” if you mean measures of the frequency range of the vocalizations; otherwise if you mean “frequency of occurrence” please explain better.

243: please briefly explain the structure/pattern of the codas with references to available literature for Med codas (to be discussed in later in the paper)

247: (12 spectrograms) ? what do you mean ?

251: the description of frequency limits is not clear. Use the expression “lower frequency limit” and “upper frequency limit”. Or just refer to the "frequency range". Also explain how the frequency range has been calculated, e.g. at -XX dB ref max amplitude in the spectrum ?

253: “click frequency rate” is incorrect: to avoid confusion don’t use the term “frequency” when you write about “rate”

256: same as 251

258: “frequency” do you mean “frequency range” ?

264, 277, 279: it is not clear the meaning of the number in parentheses

301: per second … for second … please correct

Discussion

interesting to note that your codas are different from the classical 3+1 coda reported in literature as the most common in the Med. However the 2+1 has been already reported in the Med. Also interesting to note the production of different codas by the same individual.

428: Pace et al. in parentheses rather than referenced by a number.

Biblio:

18.

For the Italian strandings database it is also worth to mention this paper, unfortunately in Italian, but the only available to describe the data bank

Pavan G., Bernuzzi E., Cozzi B., Podesta M., 2013. La rete nazionale di monitoraggio degli

spiaggiamenti di mammiferi marini. Atti 44 Congresso SIBM. Biol. Mar. Mediterr. (2013), 20:

262-263.

Reviewer #2: General comment:

The authors present two rescue operations of sperm whales entangled in driftnets in the Aeolian Archipelago. Behavioral data of both sperm whales were collected over the rescue operations. This study is not a research paper where you expect a clear biological question and associated reproductible experimental design with sufficient sample size to answer your hypothesis. This work corresponds to a case report paper which provides informative and useful material for futur similar rescue cases and for supporting regulations related to illegal use of driftnets at risk for whales’ entanglements. I recognize the great effort that was accomplished here with both the rescue process and the collection of behavioral data. This represents an obviously important piece of information, from a conservation point of view, and also for enriching our knowledge on behavioral features displayed by sperm whales under particularly stressful contexts. The manuscript contains data that deserve to be spread out into the scientific community, however, it does meet the criteria for a publication in PLOS ONE (2 report cases, and see specific comments). May I suggest a more appropriate publication of this work as a report paper in "Journal of Cetacean Research and Management" or as in "Aquatic Mammals". I list below some specific comments and suggestions that I hope will be useful to improve some aspects of the manuscript.

Specific comments :

1) Objectives and focus of the paper

In the introduction, the authors provide a rich documentation on the issue of illegal use of driftnet, highliting well the conservation problem for the species. However, a followed clear objective is missing.

I found attempts to state objectives/hypothesis to be tested here :

- in the introduction, L. 79-83 (“The study of the phases following the rescue operations can provide … increasing the chances of post-release survival.”)

- in the discussion, L 324-327 (“Combining behavioural, ... to reduce additional stress or accidental injuries during rescue operations.”).

L. 482. What would yo do during a rescue operation if acoustical features associated to an increased-stress would occur? I don’t think that such monitoring sound production would make a rescue team to decide to interrupt the rescue operation.

There is not enough material to accurately test whether acoustics can allow monitoring stress level, neither to estimate whether the protocol allowed for more or less chances of post-release survival. I recommend to maintain the focus on the actual key outcomes of the paper: i) the rich description of behavioral displays (including acoustic data) exhibited by sperm whales in particularly stressfull conditions (L. 77-78, L. 321-322), and ii) the list of valuable recommendations based on this experience study, that should be useful for potential futur rescue operations (§L. 470).

The descriptive analysis of the behavioral change over the rescue phases is interesting to document (L. 208 and L. 253 « In particular, a higher breath rate was recorded during ongoing rescue operations for both whales”, “…the click rate was higher during ongoing rescue operations”). However, to my opinion, they do not represent the most interesting findings; the paper would have overall more value and would be also attractive for a broader reader community by shaping/accentuating the focus into: providing new data on the behavioral pattern (especially on acoustic behavior) displayed by sperm whales under particularly stressfull conditions (entangled, rescue operation) and comparing it to the existing litterature, i.e. ref. on the typical natural behavior (e.g. how is it common to produce creacks for juvenile sperm whales there and for the species in general…etc), and ref. on the behavioral pattern exhibited in other stressfull contexts such as in response to an increased predation risk or other types of disturbances (e.g. man-made noise) for which there is an existing literature.

Given this highly variable context and factors, I would not focus on comparing both whales in the results section but rather would keep this in a descriptive way for the discussion, with proposing some explanation for such differences (as done in L. 366).

3) comparison across the rescue phases.

The 2 by 2 comparisons between the different phases were made (e.g. L117-118; L.217). Did the authors account for multiple comparisons (e.g. Bonferroni correction).

If the authors aim to make comparison (even an descriptive one) between whales through the different phases, it would help to provide more details of each phase and clarify the level of consistency of the phases between the whales.

-e.g. L. 103, and Figure 4: “monitoring” phase for whale #2 is actually a post-release phase with presence of operators tracking the whale in order to attempt to remove a remaining piece of net. I suggest to delete the term “monitoring” phase and instead have the “post-release” phase with (for whale #2) or without (for whale #1) tracking.

-L. 100: it is only said here that during pre-release period the “operators approached the whale” but there was also a rope that was attached to the tail as mentioned later in the text (Fig 2, and L. 144-146).

4) interpretation.

Figure 4: Do you have reference to support that those behavioral displays are stress-related ? For the increased breath rate, your justification supporting the stress state is more furnished and thus more convincing (L345-364) that for the other behavioral parameters (acoustics, and surface displays).

L. 27: “ …it collaborated during rescue operations showing only few behavioural evidences of stressful condition.”

Getting nearly quiet and hardly moving could actually indicate an extreme degree of stress. So I would not restrict the “stress-related” indicators to the agitation and movements displayed by the Whale number 2.

There are a considerable list of references but the findings are not well shown in the light of them (e.g. with what we know on the acoustic behaviour of sperm whales). I suggest to clearly present what is know on the species regarding the typical natural breath rate, and the known stressfull behavioral contexts for which particular displays such as codas were shown to be produced e.g. anti-predatory responses, etc.); this would consolidate the interpretation of the behavioral data analysis.

L. 336-337- (ref #58) : this is a ref of dolphins in zoo-captivity that showed agonistic interactions with conspecifics. Could you detail how it supports (e.g. common aspects) what was observed in the sperm whales’ behavioral displays here?

- L. 424. and L. 449. In addition to ref 41, it could be mentioned that codas can be produced in a context of anti-predator behavior which represent a particularly stressfull context for the whales (e.g. in Curé et al. 2013. Responses of male sperm whales to killer whale sounds: implications for anti-predator strategies. Sci Rep. 3:1579. doi: 10.1038/srep01579.)

- See also this additional ref for the discussion part on clicks: Tønnesen et al. 2020. The long-range echo scene of the sperm whale biosonar. Biol Lett. 16(8):20200134. doi: 10.1098/rsbl.2020.0134.

Other comments:

- L. 75, 78: “Acoustic vocalizations”. Vocalizations are “acoustics” so you can delete it. I’d actually rather talk about “acoustic behavior of” or “sounds produced”.

- L. 87 and L. 93: the authors mention the first whale as a “10m juvenile male sperm whale”. Does the gender and estimated age class can be also mentioned for the second 9m whale? Also, a more furnished description of the physical aspects of the two animals (body condition) would feed further potential explanations for the different behaviors between whales.

- Figure 4 : Why to separate the pre-release and ongoing phases if data are pooled together at the end?

- L. 367: Data do not suggest that. These are only hypotheses proposed to explain why differences are observed.

Reviewer #3: Behaviour and acoustic vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea Review of PONE-D-20-40631

This paper reports some behavioural observation of two sperm whales during operations to attempt to disentangle them from driftnet fishing gear. The observations are intersting and the lessons learned could potentially be applied to other similar situations. Unfortunately the manuscript as presented is not suitable for publication. The main problems are (1) a lack of clarity and precision in the descriptions of data collection, processing, and analysis, especially a lack of clarity over which hypothesis tests were specified a priori and why and which were conducted post-hoc having viewed the data and thus carrying much less weight. The distinction must be made clear in any revision. (2) A series of speculative and unsupported claims about vocalisation function in the discussion which are really not supported at all by the data collected, which of its nature simply is not fit to test these kinds of ideas being entirely opportunistic and observational and (3) the need to improve the written presentation with the help of a colleague with full professional proficiency in scientific English.

An ethics statement should be provided. No justification is provided for restrictions to data availability - this does not seem commensurate with contemporary scientific expectations - I do not accept that 'all relevant data are within the manuscript'. In my eyes, this compromises the integrity of the work.

L19 under which jurisdiction? Italy? EU?

L23 it is an opportunity to study 'whales in extremely stressful conditions' but why more broadly is that important?

L31 is 'single clicks' what are called regular clicks in the rest of the literature? Better to keep consistent

L33 'associating' is vague

L35 I do not support the assertion of 'alarm' and 'distress' in these vocalisations - describe the form but extra evidence is needed to ascribe function

L47 there are more recent IUCN assessments of this threat - it is changing and better to reflect the most recent assessments see Notarbartolo et alarm

L55 'national database' - which nation!? Are stranding records from 1714 really thought comparable to those in the last two decades? Maybe revise this to a more pertinent timescale.

L57 why is the location relevant? isn't it the cause we are more concerned about?

L69 why are vocalisations not a behavioural observation? Also 'acoustic vocalisation' is redundant - there aren't any non-acoustic vocalisations right?

L76 'immediately after release, and in the hours-days thereafter' the distinction between these two categories is not clear

L77-78 see point above from abstract - yes a great opportunity but to what wider relevance?

L80 '(i.e. acoustic parameters' this is not a method

L82-83 this level of effort is surely only justified if the fate of one or two individuals over a 5-10 yesr period will make a population level difference - I don't think Med sperm whales are that badly off yet. Perhaps the argument for preparedness could be used - not a major problem yet but could become vital if population trajectories continue downward

L86 I think 10:01 UTC+1 should be the standard time format throughout but the journal may have style rules

L87-94 it would be interesting to know if the nets appeared superficially similar suggesting they sourced from the same fishing operation or different

L93 no sex information for the second whale?

L96-97 it is not neccesary to describe operations down to the level of plotting points on a map - if the GIS was used to produce a particular piece of data from a geographic database, fair enough.

L100-101 what was 'pre-release' only relevant for the first whale? What was the rationale for a distinctive timeline phase? More information is needed on why different timelines were used for each whale.

L108 I think this is best written as 'counting breaths per minute' since focal observations sampling at one-minute intervals strongly suggests point sampling which I don't think it what the authors did since they refer to breathes per minute later

L113 this is confusing because the activities listed are events - the animal performed a specific behaviour like side-roll or spy hop - so how are 'percentage of each activity' calculated specifically?

L118-119 no pairwise follow up in the case of a significant KW result?

L120-122 what is the theoretical justification for expecting a monotonic if non-linear correlation between time of day and length of dive? Was this hypothesis established a priori or tested after viewing the data? The difference matters!

L123 this sentence is also true if you remove 'stressed'...

L125 give at least the hydrophone +/-3dB frequency response here and give more detail on what the 'wideband solid-state recorder' was - sampling rate? Bit depth? Make/model?

L127 I don't think 'extrapolate' is the right word here.

L128 'single clicks' is not something I recognise from the literature - do the authors mean 'regular clicks' or 'slow clicks' as characteristically produced by males?

L169 what is a 'lighting boa'? A lit mark of some kind?

L171 I think perhaps 'long dives' rather than 'deep' would be more precise here?

L173-174 this is kind of vague and speculative - what is a 'great exploration effort'? Better to say 'X boats, Y planes and Z individuals'

L198 this is exactly the same information that started the previous section - avoid this repetition

L210-211 I am unclear what is being tested here - a direct comparison is suggestd by the text specifically between whale 1 vs whale 2, in which case only pairwise tests are needed? So what was the multiple sample KW test used for? Please provide more clarity here.

L220 pretty sure this should be 'breath/minute' - if you count the breathes in a minute then divided by 60 then you get breath/second... please check and clarify

L216-217 again I am unclear how these tests are working - the KW test gives you a test of whether all the samples come from the same population but doesn't specify which categories vary, for that you need post-hoc pairwise tests

L220 this section bascially confirms to me that the test of the dive time vs time of day was a post-hoc hypothesis test and should be labelled as such (e.g. 'On inspection of the data we noticed a trend of increasing dive time through the encounter; a post-hoc Spearman rank correlation test was significant') - also specify either that no test was carried out for the other whale or report its results.

L229 the relation between recording time and number of spectrograms is a bit mysterious here

L231 this implies the same vocalisations but in a different order ('sequence') - is this what was meant?

L236 Table 1 I am now more convinced that 'single clicks' is a misnomer here - there are a lot of them!

L248-249 - this sounds like normal foraging echolocation - better reference to existing literature should be made here e.g. Gannier and collegues' analyses of foraging sperm whale vocalisations

L251 there appears to have been some frequency domain signal processing analysis here but the details are miissing please provide full methodological details for recording the click bandwidths - e.g. was it a -10dB standard bandwidth for transients? Or a spectral analysis, in which case to what resolution? Was the range 'eyeballed' off the spectrogram? If so were multiple observers used to check for consistency? I think we can expect that these methodological checks should be performed for publication in a journal of Plos One stature.

L257-263 agains these tests are poorly described and poorly justified - why do we care about these details? No framework of hypotheses was introduced, these just give the impression of being run ad-hoc after viewing the data, which is fine but should be labelled as such to avoid giving misleading ideas about the strength of the statistical findings.

L300 unclear how these rates were calculated - if there were other types of codas produced between examples of 'coda_1' then how is this meaningful (i.e. if the sequence was coda_1, coda_2, coda_1 why does it make sense to measure the rate of coda_1 occurence? No justification is provided, which gives the ijmpression the theoretical framework of this paper requires more work.

L302 this is confusing me between measure of coda duration and of inter-coda intervals

L324 'gain a better understanding' is quite vague - what specifically did we gain in terms of understanding? What do we understand now that we did not before?

L328 A rather obvious possibility for the different behaviours seems to have been missed here - is it not possible the less active whale had been entangled longer before encounter? Mention is made of numerous injuries and lacerations which suggests a prolonged interaction and perhaps the animal was just exhuasted?

L346 what is the difference between ''surfacing' and 'naturally resting'?

L358-360 maybe just me but I fail to see how the data reported support the assertion here that it is tail weight rather than vessel and human proximity that is causing the elevated ventilation rate...

L373 why isn't this used before! It would make much more sense to described these as 'usual' or better as 'clicks resembling regular echolocation clicks' if there is doubt, and justify earlier in the light of the slow repetition rates...

L379 more often referred to as 'slow clicks' in contemporary literature

L383 I think the authors mean that usual clicks are usually produced in prolonged bouts interspersed with buzzes rather than the clicks themselves being a long duration vocalisation, which they are not

L403-404 more is needed beyond assertion that this was not typical socialising creak

L412 I fundamentally disagree that the data here provide the basis for this assertion of 'distress creaks' and the reference to 'fear screams' is obscure indeed whie the comparison to dolphin whistles and similar duration humpback calls is very weak. This should be struck as it a conclusoin that is fundamentally unsupported by the data.

L433 I don't accept that sufficient evidence to differentiate between a 1+2+1 pattern and a 3+1 pattern has been presented. This speculation should be removed.

L437 this speculation goes way beyond the data. It should be removed. There is nothing here that can speak to clan structure.

L448 the same is true of the speculation about alarm codas here

L462-464 the use of language like this is unlikely to lead to productive and problem solving collaborations with the fishing industry on this issue. I suggest a moderation. Also the basis for asserting that the whale as cut out of a 'live' net rather than entangled in a small amount of abdanonded 'ghost' gear is not clear...

There are numerous linguistic glitches. The manuscript needs the attention of a colleague with full professional proficiency in scientific English - here I list the errors in the introduction and abstract only but they are pervasive through the entire manuscript and need careful editing: L24 'during rescue operation' L37 'efficient standardized rescuing protocol application' L35 'follow the animal physical/psychological states' L43 'shown by genetic evidences' L45 'counting less than' L61 'the morphological aspects of the bathy-morphological setting' L63 'makes no exception' L66 'and successively stranded dead' L71 'the acoustic analysis were conducted' L73 'documented other two sperm whales’ entanglement'

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PLoS One. 2021 Apr 29;16(4):e0250888. doi: 10.1371/journal.pone.0250888.r002

Author response to Decision Letter 0

14 Mar 2021

Response to Editor’s comments

AR in this file is Authors Reply

Editor Comments:

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When submitting your revision, we need you to address these additional requirements.

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AR: Thank you for providing us the necessary information to meet journal formatting requirements. We change our format accordingly.

We require you to either (1) present written permission from the copyright holder to publish these figures specifically under the CC BY 4.0 license, or (2) remove the figures from your submission:

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The following resources for replacing copyrighted map figures may be helpful:

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Maps at the CIA (public domain): https://www.cia.gov/library/publications/the-world-factbook/index.html and https://www.cia.gov/library/publications/cia-maps-publications/index.html

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Landsat: http://landsat.visibleearth.nasa.gov/

USGS EROS (Earth Resources Observatory and Science (EROS) Center) (public domain): http://eros.usgs.gov/#

Natural Earth (public domain): http://www.naturalearthdata.com/

AR: thank you for your suggestions. We have replaced Figure 1 with one processed ex novo. The actual figure shows only data reproduced by ourselves on the basis of public domain layers (source: https://glovis.usgs.gov/ with personal account and https://www.gebco.net/data_and_products/gridded_bathymetry_data/#a1-) and data (source: http://www.naturalearthdata.com/).

Response to Reviewers' comments

Reviewer's Responses to Questions:

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Partly

________________________________________

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: I Don't Know

________________________________________

3. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

________________________________________

4. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

________________________________________

5. Review Comments to the Author

REVIEWER #1: REVIEW PLOSONE D-20-40631

This paper presents an interesting description of two net entangling events that occurred to sperm whales around the Aeolian Islands in the lower Tyrrhenian Sea. The authors describe the disentangling operations and the associated behaviour of the two animals during the rescue operation. The paper is pretty descriptive, and scientific results are limited to a description of occurred behaviours, rather than a scientific interpretation; however, the paper depicts the problem of illegal driftnets and gives cues and recommendations about how to face such entangling events and related rescue operations. Considering this, I recommend the publication with a minor revision to correct some inconsistencies and ambiguities in the acoustic behaviour description. Overall, it is a very interesting lecture on an unusual and poorly known event.

AR: thank you for the useful comments and revisions. This paper aims to highlight the lack of a rescuing protocol in our area and, at the same time, providing useful data on distressed sperm whales.

124: please add more information on recording: depth of the hydrophone? sampling rate of the recorder?

AR: done. We added depth, sampling rate, and sensibility of the hydrophone.

127: measure rather than “extrapolate”

AR: changed

127: frequency parameters rather than just “frequency” if you mean measures of the frequency range of the vocalizations; otherwise, if you mean “frequency of occurrence” please explain better.

AR: thank you for the explanation. We were referring to upper and lower frequency limits

243: please briefly explain the structure/pattern of the codas with references to available literature for Med codas (to be discussed in later in the paper)

AR: added coda structures and references.

247: (12 spectrograms)? what do you mean?

AR: it is actually the number of sound files that we analysed, but we realize that it is redundant information, removed

AR: we reported the range of the lower and the upper limits of the frequencies detected. We did not calculate the frequency range.

253: “click frequency rate” is incorrect: to avoid confusion don’t use the term “frequency” when you write about “rate”

AR: removed “frequency”

256: same as 251

AR: thank you, we corrected here as well

258: “frequency” do you mean “frequency range”?

AR: we meant the mean frequency as result of the upper and the lower limit measured in Raven, but we have few data to do a comparison so we removed from the revised manuscript this result.

264, 277, 279: it is not clear the meaning of the number in parentheses

AR: it is the SD journal format. For more clarity, we added (SD), before the actual figures

301: per second … for second … please correct

AR: corrected

Discussion

AR: Thank you for your interest to these data. We found very interesting as well the production of different codas by the same individual, and we are going to analyse coda types from different individuals in the same area.

428: Pace et al. in parentheses rather than referenced by a number.

AR: corrected

Biblio:

18. For the Italian strandings database it is also worth to mention this paper, unfortunately in Italian, but the only available to describe the data bank:

Pavan G., Bernuzzi E., Cozzi B., Podesta M., 2013. La rete nazionale di monitoraggio degli spiaggiamenti di mammiferi marini. Atti 44 Congresso SIBM. Biol. Mar. Mediterr. (2013), 20: 262-263.

AR: substitute to the old reference

REVIEWER #2: GENERAL COMMENT:

The authors present two rescue operations of sperm whales entangled in driftnets in the Aeolian Archipelago. Behavioral data of both sperm whales were collected over the rescue operations. This study is not a research paper where you expect a clear biological question and associated reproductible experimental design with sufficient sample size to answer your hypothesis. This work corresponds to a case report paper which provides informative and useful material for future similar rescue cases and for supporting regulations related to illegal use of driftnets at risk for whales’ entanglements. I recognize the great effort that was accomplished here with both the rescue process and the collection of behavioral data. This represents an obviously important piece of information, from a conservation point of view, and also for enriching our knowledge on behavioral features displayed by sperm whales under particularly stressful contexts. The manuscript contains data that deserve to be spread out into the scientific community, however, it does meet the criteria for a publication in PLOS ONE (2 report cases, and see specific comments). May I suggest a more appropriate publication of this work as a report paper in "Journal of Cetacean Research and Management" or as in "Aquatic Mammals". I list below some specific comments and suggestions that I hope will be useful to improve some aspects of the manuscript.

AR: thank you for the comments and suggestions. We appreciate your advice, even though we believe that PLOS ONE is a more suitable journal where to publish our work. This paper is not only a case study paper including the behaviour of these two entangled animals, but it reports data that can be used to properly address rescue operation outputs or as a reference point for other studies. The cited journals are too specific in our opinion and the take-home message of our paper could be lost.

Specific comments:

1) Objectives and focus of the paper

In the introduction, the authors provide a rich documentation on the issue of illegal use of driftnet, highlighting well the conservation problem for the species. However, a followed clear objective is missing.

I found attempts to state objectives/hypothesis to be tested here:

- in the introduction, L. 79-83 (“The study of the phases following the rescue operations can provide … increasing the chances of post-release survival.”)

- in the discussion, L 324-327 (“Combining behavioural, ... to reduce additional stress or accidental injuries during rescue operations.”).

AR: We have expanded the objectives and focus the paper as suggested.

L. 482. What would you do during a rescue operation if acoustical features associated to an increased-stress would occur? I don’t think that such monitoring sound production would make a rescue team to decide to interrupt the rescue operation.

AR: we appreciate your comment, but we believe that acoustics could be useful to warn the operators to use more caution or decrease the number of people around the animal or understand if the animal is getting nervous or not. We state it in the recommendation section.

There is not enough material to accurately test whether acoustics can allow monitoring stress level, neither to estimate whether the protocol allowed for more or less chances of post-release survival. I recommend to maintain the focus on the actual key outcomes of the paper: i) the rich description of behavioral displays (including acoustic data) exhibited by sperm whales in particularly stressful conditions (L. 77-78, L. 321-322), and ii) the list of valuable recommendations based on this experience study, that should be useful for potential future rescue operations (§L. 470).

AR: thank you for the feedback. We removed from the revised manuscript any assumption that is not sustained by data.

The descriptive analysis of the behavioral change over the rescue phases is interesting to document (L. 208 and L. 253 « In particular, a higher breath rate was recorded during ongoing rescue operations for both whales”, “…the click rate was higher during ongoing rescue operations”). However, to my opinion, they do not represent the most interesting findings; the paper would have overall more value and would be also attractive for a broader reader community by shaping/accentuating the focus into: providing new data on the behavioral pattern (especially on acoustic behavior) displayed by sperm whales under particularly stressful conditions (entangled, rescue operation) and comparing it to the existing literature, i.e. ref. on the typical natural behavior (e.g. how is it common to produce creaks for juvenile sperm whales there and for the species in general…etc), and ref. on the behavioral pattern exhibited in other stressful contexts such as in response to an increased predation risk or other types of disturbances (e.g. man-made noise) for which there is an existing literature.

AR: thank you for the advice, we added this part at the beginning of the discussion session along with references.

2) I don’t see the relevance to statistically compare the behavior of both whales (e.g. L. 282: comparison of number of creaks between both whales): the sample size is critically low (n=2), there is no data on the whales’ baseline behavior to assess for a natural inter-individual variability, the timing at which whales had been entangled when discovered is unknown, and there were additional factors (e.g. inconsistencies of the rescue operation phases across whales, external factors like number of boats present in the area etc) that might also have influenced the whales’ behavior. Given this highly variable context and factors, I would not focus on comparing both whales in the results section but rather would keep this in a descriptive way for the discussion, with proposing some explanation for such differences (as done in L. 366).

AR: we appreciate your suggestion and we agree with your comment including in the new version of the manuscript the possibility that different factors may be involved in the observed behavioural pattern. As suggested, we removed the behavioural comparison between whales in the results section. However, we retain the acoustical comparison, because we believe that it could be useful for future studies and underline eventual inter-individual differences.

3) comparison across the rescue phases.

AR: We confirmed our results using a KW followed by a pairwise Mann-Witney test with Bonferroni correction.

If the authors aim to make comparison (even a descriptive one) between whales through the different phases, it would help to provide more details of each phase and clarify the level of consistency of the phases between the whales.

AR: We rewrote that part in order to clearly state the consistency of the phases between whales. We accept your suggestion to rename some phases, agreeing that “monitoring” is not accurate. We change that in “Following”, because in that phase we actually followed the escaping whale. We also change “ongoing” in “rescuing”, “pre-release” in “pre-rescue” and “post-release” in “post-rescue”, more in line with the description of the main event happened in that phase.

4) interpretation.

Figure 4: Do you have reference to support that those behavioral displays are stress-related? For the increased breath rate, your justification supporting the stress state is more furnished and thus more convincing (L345-364) that for the other behavioral parameters (acoustics, and surface displays).

AR: we removed any reference to stress-related. We agree that although our data seems to support this hypothesis, the sample size is too limited.

L. 27: “ …it collaborated during rescue operations showing only few behavioural evidences of stressful condition.”

AR: we removed that sentence.

There are a considerable list of references but the findings are not well shown in the light of them (e.g. with what we know on the acoustic behaviour of sperm whales). I suggest to clearly present what is known on the species regarding the typical natural breath rate, and the known stressful behavioral contexts for which particular displays such as codas were shown to be produced (e.g. anti-predatory responses, etc.); this would consolidate the interpretation of the behavioral data analysis.

AR: As suggested in the revised manuscript we better clarified the typical natural breath of a sperm whale during surfacing and before diving in the discussion. The behavioural contexts in which codas are produced is in the new version of the manuscript clearer referring to a lot of bibliography. In addition, as our codas were herd from whales in a stressful behavioural context, we preferred to keep the discussion in terms of the possible role of some behavioural/acoustic factors to non-invasively measure the stress levels of entangled whales.

L. 336-337- (ref #58): this is a ref of dolphins in zoo-captivity that showed agonistic interactions with conspecifics. Could you detail how it supports (e.g. common aspects) what was observed in the sperm whales’ behavioral displays here?

AR: We retained the reference. The reference reports an example of agonistic behaviour especially used for threat conspecific. We use this reference to suggest another interpretation of the behavioural displays observed in the study that should be threatening the rescuers.

- L. 424. and L. 449. In addition to ref 41, it could be mentioned that codas can be produced in a context of anti-predator behavior which represent a particularly stressful context for the whales (e.g. in Curé et al. 2013. Responses of male sperm whales to killer whale sounds: implications for anti-predator strategies. Sci Rep. 3:1579. doi: 10.1038/srep01579.)

AR: thank you for the suggestion. Added (ref #101)

- See also this additional ref for the discussion part on clicks: Tønnesen et al. 2020. The long-range echo scene of the sperm whale biosonar. Biol Lett. 16(8):20200134. doi: 10.1098/rsbl.2020.0134.

AR: we appreciate the advice. We added this reference as a substitute for ref#79, which was quite outdated (1966).

Other comments:

- L. 75, 78: “Acoustic vocalizations”. Vocalizations are “acoustics” so you can delete it. I’d actually rather talk about “acoustic behavior of” or “sounds produced”.

AR: done in the whole manuscript.

AR: We added the requested information.

- Figure 4: Why to separate the pre-release and ongoing phases if data are pooled together at the end?

AR: Because the pre-release phase includes rescue preparations (i.e. secure the animal tail with a rope), which has not happened for the second whale. In the revised version of the manuscript (methods) a new classification of the different phases was done including those that were in common for both whales and those that were only for one.

- L. 367: Data do not suggest that. These are only hypotheses proposed to explain why differences are observed.

AR: removed

Reviewer #3: Behaviour and acoustic vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea Review of PONE-D-20-40631

This paper reports some behavioural observation of two sperm whales during operations to attempt to disentangle them from driftnet fishing gear. The observations are interesting and the lessons learned could potentially be applied to other similar situations. Unfortunately, the manuscript as presented is not suitable for publication. The main problems are (1) a lack of clarity and precision in the descriptions of data collection, processing, and analysis, especially a lack of clarity over which hypothesis tests were specified a priori and why and which were conducted post-hoc having viewed the data and thus carrying much less weight. The distinction must be made clear in any revision. (2) A series of speculative and unsupported claims about vocalisation function in the discussion which are really not supported at all by the data collected, which of its nature simply is not fit to test these kinds of ideas being entirely opportunistic and observational and (3) the need to improve the written presentation with the help of a colleague with full professional proficiency in scientific English.

AR: thank you for the feedback, comments and suggestions. We agree with most of your comments and we strongly revised the manuscript to make it more suitable for publication. (1) We agree that some sections are not clearly explained and some terms are used incorrectly, making the reading flow very confusing and changed them in the revised version. (2) We agree with that too and removed speculations and unsupported hypothesis from the discussion (3) The scientific English of the manuscript was revised by a full-proficiency colleague before resubmission.

AR: We claim in the acknowledgments that any ethics statement needs to be provided because we do not handle any animal. However, we state the owned permits in the acknowledgments too. About data restriction, we disagree. Our datasets derive from two emergency events, so may be limited by rescue operations and the difficulty of the situation (moving the boat, collaborate with the rescue team, etc.). We confirm that all relevant data recorded in this study are included in this manuscript.

L19 under which jurisdiction? Italy? EU?

AR: Rewrote: in different Mediterranean areas, primarily in the Tyrrhenian Sea

L23 it is an opportunity to study 'whales in extremely stressful conditions' but why more broadly is that important?

AR: thank you for the comment. We rewrote the sentence.

L31 is 'single clicks' what are called regular clicks in the rest of the literature? Better to keep consistent

AR: thank you for the suggestion, but we prefer to retain ‘single click’ in the revised manuscript due to the particular nature of this study. We cannot assume a priori that those sounds could be what literature call ‘regular clicks’ or “slow clicks” for the characteristics of this vocalizations. Particularly, in this study, the term ‘single clicks’ is used to indicate those sounds which resembling regular echolocation clicks (“usual clicks”) associated primarily with a foraging behaviour but with some substantial differences with surface clicks or slow clicks (unknown behavioural function and peculiar ICI). We better clarify clicks classification in the revised manuscript and compared results with the available literature.

L33 'associating' is vague

AR: changed in ‘comparing’.

L35 I do not support the assertion of 'alarm' and 'distress' in these vocalisations - describe the form but extra evidence is needed to ascribe function

AR: We remove that part and other speculations from the revised manuscript.

L47 there are more recent IUCN assessments of this threat - it is changing and better to reflect the most recent assessments see Notarbartolo et alarm

AR: thank for the correction. Changed reference #3 as suggested.

L55 'national database' - which nation!? Are stranding records from 1714 really thought comparable to those in the last two decades? Maybe revise this to a more pertinent timescale.

AR: changed ‘national’ with ‘Italian’ and reduced the timescale to the last two decades (2000-2020).

L57 why is the location relevant? isn't it the cause we are more concerned about?

AR: In the area is not already instituted a Marine Protected Area so we want to give more importance to the location context and critical situation.

L69 why are vocalisations not a behavioural observation? Also 'acoustic vocalisation' is redundant - there aren't any non-acoustic vocalization, right?

AR: removed or changed with ‘acoustic behaviour’.

L76 'immediately after release, and in the hours-days thereafter' the distinction between these two categories is not clear

AR: removed, it is clearly explained in M&M.

L77-78 see point above from abstract - yes a great opportunity but to what wider relevance?

AR: we rewrote this section and explained better the aim of the study.

L80 '(i.e. acoustic parameters' this is not a method

AR: changed ‘parameters’ into “recordings”.

L82-83 this level of effort is surely only justified if the fate of one or two individuals over a 5-10 years period will make a population level difference - I don't think Med sperm whales are that badly off yet. Perhaps the argument for preparedness could be used - not a major problem yet but could become vital if population trajectories continue downward

AR: removed ‘thus increasing the chances of post-release survival‘

L86 I think 10:01 UTC+1 should be the standard time format throughout but the journal may have style rules

AR: The journal does not provide any specific time format, so we are accepting your suggestion. Thank you.

L87-94 it would be interesting to know if the nets appeared superficially similar suggesting they sourced from the same fishing operation or different

AR: Unfortunately, we did not have the opportunity to do this investigation because the nets were subtracted by the Coast Guard.

L93 no sex information for the second whale?

AR: It seems to be a male but we don’t have a clear image to confirm this. We kept the distance for not disturbing the animal and the rescue operations during the two events. The second whale was very nervous and from a distance was not possible for us to identify the sex with the GoPro videos. We asked to a video-operator, one of the people not involved in rescue operations which was very close to the individual (and cause of stress for him) to provide us some screen shots of the ventral area in order to identify the sex but he did not reply to our request. The videos of this video maker were used to produce a documentary for the television but not for scientific purposes.

L96-97 it is not necessary to describe operations down to the level of plotting points on a map - if the GIS was used to produce a particular piece of data from a geographic database, fair enough.

AR: removed

AR: We agree that this section is very confusing. We have rewritten the sentence.

AR: We better explained and corrected this sentence. Both breaths and behaviour were recorded at one-minute intervals and these were sampled at the same time. We recorded the number of behavioural events for minute and for the entire duration of each phase.

AR: The behaviour of the sperm whales was recorded at one-minute intervals (sets). We recorded the number of behavioural events for each set. The percentage of each activity was calculated as number of events/number of sets in the different phases.

L118-119 no pairwise follow up in the case of a significant KW result?

AR: We performed new tests to confirm our results: Mann-Whitney test and the Bonferroni correction for KW.

AR: we removed the regression analysis on these data from the results.

L123 this sentence is also true if you remove 'stressed'...

AR: done.

L125 give at least the hydrophone +/-3dB frequency response here and give more detail on what the 'wideband solid-state recorder' was - sampling rate? Bit depth? Make/model?

AR: added.

L127 I don't think 'extrapolate' is the right word here.

AR: changed in ‘measured’.

L128 'single clicks' is not something I recognise from the literature - do the authors mean 'regular clicks' or 'slow clicks' as characteristically produced by males?

AR: thank you for the suggestion, we better clarify clicks classification in the revised manuscript. We prefer to retain ‘single click’ in the revised manuscript due to the particular nature of this study. We cannot assume a priori that these clicks could be what the literature call ‘regular clicks’ or “slow clicks” (added in Methods). Particularly, in this study, the term ‘single clicks’ is used to indicate those sounds which resembling regular echolocation clicks (“usual clicks”) associated primarily with a foraging behaviour but with some substantial differences with surface clicks or slow clicks (unknown behavioural function and peculiar ICI). In the discussion we added these considerations and compare the characteristics of these vocalizations with those found in other studies.

L169 what is a 'lighting boa'? A lit mark of some kind?

AR: changed ‘lighting boa’ in ‘lit mark buoy’.

L171 I think perhaps 'long dives' rather than 'deep' would be more precise here?

AR: changed as suggested. We don’t know how deep the whale descended.

L173-174 this is kind of vague and speculative - what is a 'great exploration effort'? Better to say 'X boats, Y planes and Z individuals

AR: we removed that sentence, because we don’t know the actuals figures of this effort.'

L198 this is exactly the same information that started the previous section - avoid this repetition

AR: we used the same method for both behavioural and respiratory patterns, but, yes, we agree that it could be confusing. Rewrote by referring to the behavioural data.

L210-211 I am unclear what is being tested here - a direct comparison is suggested by the text specifically between whale 1 vs whale 2, in which case only pairwise tests are needed? So, what was the multiple sample KW test used for? Please provide more clarity here.

AR: We better explained in methods and results

L220 pretty sure this should be 'breath/minute' - if you count the breathes in a minute then divided by 60 then you get breath/second... please check and clarify

AR: sorry, it was a misspelled error, corrected.

AR: We confirmed our results running a KW followed by Mann-Whitney test with Bonferroni correction.

L220 this section basically confirms to me that the test of the dive time vs time of day was a post-hoc hypothesis test and should be labelled as such (e.g. 'On inspection of the data we noticed a trend of increasing dive time through the encounter; a post-hoc Spearman rank correlation test was significant') - also specify either that no test was carried out for the other whale or report its results.

AR: we rewrote this section according to our suggestion. Thank you.

L229 the relation between recording time and number of spectrograms is a bit mysterious here

AR: We apologize, spectrograms were meant as the number of files analysed. It is a redundant information, as we already have the recording time.

L231 this implies the same vocalisations but in a different order ('sequence') - is this what was meant?

AR: yes

L236 Table 1 I am now more convinced that 'single clicks' is a misnomer here - there are a lot of them!

AR: Already explained before.

L248-249 - this sounds like normal foraging echolocation - better reference to existing literature should be made here e.g. Gannier and collegues' analyses of foraging sperm whale vocalisations

AR: thank you for the advice, we substitute ref#51 with your suggestion.

L251 there appears to have been some frequency domain signal processing analysis here but the details are missing please provide full methodological details for recording the click bandwidths - e.g. was it a -10dB standard bandwidth for transients? Or a spectral analysis, in which case to what resolution? Was the range 'eyeballed' off the spectrogram? If so were multiple observers used to check for consistency? I think we can expect that these methodological checks should be performed for publication in a journal of Plos One stature.

AR: We believe that those analysis weren’t pertinent with the aim of the paper, which is a descriptive report of two entanglement events. Those kinds of data would be used for a more complete study of vocalizations of foraging sperm whales in the area.

L257-263 against these tests are poorly described and poorly justified - why do we care about these details? No framework of hypotheses was introduced, these just give the impression of being run ad-hoc after viewing the data, which is fine but should be labelled as such to avoid giving misleading ideas about the strength of the statistical findings.

AR: Better described and more justified the statistic in the revised manuscript. KW tests with correction and Mann-Whitney included in M&M and results

L300 unclear how these rates were calculated - if there were other types of codas produced between examples of 'coda_1' then how is this meaningful (i.e. if the sequence was coda_1, coda_2, coda_1 why does it make sense to measure the rate of coda_1 occurrence? No justification is provided, which gives the impression the theoretical framework of this paper requires more work.

AR: maybe this part was a bit misleading. Coda 1 was the first sequence of coda emissions between the two creak events. Coda 2 was the second sequence of coda emission after the second creak sequence. So, we calculated the coda rates for the two sequences and compare them.

L302 this is confusing me between measure of coda duration and of inter-coda intervals

AR: we apologize, we used some terms unproperly. Corrected.

L324 'gain a better understanding' is quite vague - what specifically did we gain in terms of understanding? What do we understand now that we did not before?

AR: we change ‘better’ with ‘wider’.

AR: yes, we explain it afterward.

L346 what is the difference between ''surfacing' and 'naturally resting'?

AR: none. Deleted.

AR: we agree, it was a speculation. Removed.

AR: thank you for the suggestion. Added a statement in ‘single clicks’ results section.

L379 more often referred to as 'slow clicks' in contemporary literature

AR: added specification for slow clicks.

AR: thank you for the specification. Changed.

L403-404 more is needed beyond assertion that this was not typical socialising creak

AR: we removed that sentence and rewrote the entire section, in order to be more consistent to data and literature.

L412 I fundamentally disagree that the data here provide the basis for this assertion of 'distress creaks' and the reference to 'fear screams' is obscure indeed while the comparison to dolphin whistles and similar duration humpback calls is very weak. This should be struck as it a conclusion that is fundamentally unsupported by the data.

AR: we moderate our statements to make them more consistent with data, but we are not excluded this possibility.

L433 I don't accept that sufficient evidence to differentiate between a 1+2+1 pattern and a 3+1 pattern has been presented. This speculation should be removed.

AR: thank you for the suggestion. Removed.

L437 this speculation goes way beyond the data. It should be removed. There is nothing here that can speak to clan structure.

AR: we agree. Removed

L448 the same is true of the speculation about alarm codas here

AR: as L412 comment, we moderate our statements to make them more consistent with data, but we are not excluded this possibility.

L462-464 the use of language like this is unlikely to lead to productive and problem-solving collaborations with the fishing industry on this issue. I suggest a moderation. Also the basis for asserting that the whale as cut out of a 'live' net rather than entangled in a small amount of abdanonded 'ghost' gear is not clear...

AR: thank you for the suggestion. We removed that phrase. The basis of asserting that the whale cut out a live net is solid, because that kind of net is illegal in the Mediterranean Sea since 1998. So, it can’t be abandoned.

AR: Thank you, we will surely submit the entire manuscript to an English full-proficiency colleague.

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PLoS One. doi: 10.1371/journal.pone.0250888.r003

Decision Letter 1

Patrick J O Miller

24 Mar 2021

PONE-D-20-40631R1

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

PLOS ONE

Dear Dr. Blasi,

==============================

You have addressed positively the substantial suggestions of the reviewers. However, the article still contains English errors and one unsupported claim that should be de-emphasized in your manuscript. I am therefore providing herein a detailed list of changes required for the manuscript to be acceptable, both in terms of content and presentation. Hopefully all of the suggestions will be agreeable to you, but if not, please detail point by point in your response letter any that you do not accept.

==============================

Please submit your revised manuscript by May 08 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

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An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Patrick J. O. Miller

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Additional Editor Comments (if provided):

You have addressed positively the substantial suggestions of the reviewers. However, I find that the article still contain errors and one unsupported claim that should be de-emphasized in your manuscript. I am therefore providing herein a detailed list of changes required for the manuscript to be acceptable, both in terms of content and presentation.

Major content change. Your observations were important, but limited. There is not sufficient scientific content in your report to ascribe reasons for outcomes in the two release attempt scenarios. While it might be that the presence of more boats was a factor causing higher responsiveness in the second whale, you cannot test that scientifically. Therefore, I suggest you cut the final sentence from the abstract, and significantly shorten the “Recommendations” section related to guidance of rescue protocols. I suggest any recommendations you state here should follow those of the Hamer and Minton publication. For example, on pg 13, those authors state “a quieter environment (less situational stress)… will increase the likelihood of survival…”.

Therefore, I suggest the recommendations section be cut down to a simple paragraph in which you emphasize guidance already published (citing the source) as much as possible. The one specific contribution your study makes is the benefit of including a hydrophone to observe the sounds of the whales during release attempts, as these might be helpful to interpret the state of the animal during operations.

The other detailed suggestions below are based upon my detailed review of the manuscript. I hope you will be able to accept them all.

Ln 26: change ‘provide’ to ‘collect’

Ln 27: change ‘notably’ to ‘likely’

Lns 31, 32, and throughout: change ‘breath rate’ to ‘breathing rate’

Ln 31 – report here the observed breathing rate for the first animal

Ln 32 – report here the observed breathing rate for the second animal

Ln 36 – after ‘single clicks’ insert “ – likely either slow clicks or regular clicks” ((this is necessary as ‘single click’ is not an accepted form of click type in the sperm whale literature, as pointed out by reviewer 3))

Lns 36-37: change “By comparing all data it was found that” to “Our observations indicate that”

Ln 37: change “animal’s physical/physiological status” to “physical/physiological status of sperm whales” -- this is the key scientific contribution of this report.

Delete the last sentence in the abstract, which is 1) controversial and 2) not scientifically supported by the paper. This sort of suggestion should only be mentioned in the discussion where some ancillary material is acceptable. I suggest you use positive wording for this point.

Ls 45 – change “Atlantic one” to “Atlantic population”

Ln 46 – change ‘this population’ to ‘the Mediterranean’

Ln 48 – insert “a” before “concerning matter”

Ln 48 – interest ‘the’ before “international”

Ln 65 – change ‘makes’ to ‘is’

Ln 74 – add ‘as sounds could not be ascribed to individual whales’ after ‘social unit’

Ln 77 – add ‘production’ after ‘acoustic’

Lns 79-80 – delete ‘intense’ before ‘stressful’

Lns 80 – 86 delete these two sentences here, as they belong in the discussion. The text to this point provides adequate motivation and background.

Ln 96 – change ‘shown’ to ‘had’

Ln 99 – change ‘Genre’ to ‘Sex’

Ln 105 – use past tense to refer to your specific study results, so change ‘are’ to ‘were’

Ln 106 – change ‘are described as follow’ to ‘were’

Ln 108 – change ‘specific phases for’ to ‘phases specific to’

Ln 115 – change ‘ has been observed, which was described as’ to ‘was observed: ’

Ln 117 – change ‘has been’ to ‘were’

Ln 123 – change ‘has been’ to ‘was’

Ln 129 – change ‘percentage’ to ‘rate’ (this is number per unit time). It should be reported as a number per unit time

Ln 136 – delete ‘mainly’

Ln 149 – delete ‘for’

Lns 149-150 change ‘for “single clicks” are intended sequences of clicks (ICI > 1 s) , not organized in a defined structure, similar to ‘usual click’ described in literature [39]’ to ‘ “single clicks” were scored for sequences of clicks (ICI > 1 s) that were not organized in a defined structure, as described for ‘usual clicks’ [39]’

Ln 154 – delete ‘post-hoc’

Ln 172 – state here the date the second whale was sighted

Ln 176 – add ‘for small cetaceans’ after ‘recommended’

Ln 192 – delete ‘of which’

Ln 193 and Figure 4 – the methods describe this as the number of events divided by the total number of sessions. Therefore, this is a rate. The Y-axes should be number of events per unit time.

Ln 202 – add “the” before “post-rescue”

Ln 205 – add ‘remained attached’ after ‘net’

Fig 5 legend or Y-axis must state what is the number – ie “breaths/minute”

Ln 219 – add ‘bin’ after ‘minute’.

Your statistic treats each one minute bin as an independent data sample, leading to a high sample size of measurements. Therefore, you need to be clear that you are comparing breaths per BIN specifically.

Ln 238 – change ‘are’ to ‘were’

Ln 241 – Delete “The first part of dataset included 56 minutes of acoustic recordings that were analysed for” and add ‘were analysed’ after “(18 July)”

Ln 244 change ‘differed in’ to ‘differed between’

Ln 254 – delete ‘Whereas, ‘

Ln 259 – change “The second part of dataset included 1519 minutes (from 19:04 to 06:15) of acoustic recordings of second whale’ re-sighting on 5th October.” To “An additional 1519 minutes (from 19:04 to 06:15) of acoustic recordings were recorded during the second whale’s re-sighting on 5th October.”

Ln 272 – state the sample size for this KW test.

Ln 274 – change ‘first one’ to ‘first whale’

Ln 282 – change ‘has been’ to ‘were’

Ln 293 – change ‘higher trains duration’ to ‘higher train duration’

Lns 294-297. Specify the samples sizes used for all statistical tests.

Ln 303 – change ‘observed’ to ‘noted’

Ln 316 – change ‘smaller’ to ‘lower’

Fig 9 legend – Change “Coda types spectrograms” to “Spectrograms of coda types”

Ln 326 – change “3-clicks” to “3-click”

Ln 331 – change ‘a stressed’ to ‘active’

Ln 336 – change “pattern, especially on acoustic’ to “patterns, including acoustic”

Ln 338 – change “outputs” to “resulting observations”

Ln 345 – change “brought to free” to “successfully freed”

Ln 347 – change ‘run away’ to ‘swim away’

Ln 348 change “whales’s” to “whales’”

Ln 363 – add “The” before ‘First whale”

Ln 364 – add “The” before “second whale”, and add “the” before “first” on the same line

Ln 365 – change “to the hypothesis” to “with the hypothesis”

Ln 386 – change “resembling” to “resembled”

Ln 387 – change “a foraging behaviour” to “echolocation-based foraging”

Ln 389 – change ‘are very low’ to ‘were very low’

Ln 394 – change “are used” to “were used”

Ln 395 – delete “eventual”

Ln 396 – change “do not fit” to “did not fit”

Ln 399 – change ‘in accordance with the stress level’ to ‘in accordance with the activity level’

Ln 401 -change “triggered by high-stress” to “during high activity”

Ln 409 – change “sight” to “encounter” both times.

Ln 414 – use past tense. Change “are” to “were” and “share” to “shared”

Ln 415 – change “are” to “were”

Ln 416 – change “stressful” to “entanglement”

Ln 418 – change ‘are definitely’ to ‘were definitely’

Ln 421 – change ‘show’ to ‘had’

Ln 423 – add “were” before “operating”

Ln 425 – change “to high” to “with high”

Ln 434 – change ‘enough’ to ‘sufficient’ and change “meaning” to “function”

Ln 437 – change “have known” to “are known”

Ln 449 – change “are” to “were”

Ln 453 – change “are more” to “were more”

Ln 460 – change “Orchinus” to “Orcinus”

Ln 461 – change “heard” to “produced”

Ln 474 – I don’t think this is the first, nor is it important if it is the first or not. See Esch et al 2009 Whistles as Potential Indicators of Stress in Bottlenose Dolphins. Journal of Mammalogy.

Ln 484 – delete “several” before “boats”

Ln 508 – change to “Acknowledgements”

Ln 518 – change “any ethics statement is” to “no ethics statement is required”

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

PLoS One. 2021 Apr 29;16(4):e0250888. doi: 10.1371/journal.pone.0250888.r004

Author response to Decision Letter 1

6 Apr 2021

AR in this file is Authors Reply

Response to Editor’s comments

Journal Requirements:

AR: we rechecked all the reference list and corrected eventual formatting errors, in accordance with PLOSONE guidelines.

Additional Editor Comments (if provided):

You have addressed positively the substantial suggestions of the reviewers. However, I find that the article still contains errors and one unsupported claim that should be de-emphasized in your manuscript. I am therefore providing herein a detailed list of changes required for the manuscript to be acceptable, both in terms of content and presentation.

AR:

The other detailed suggestions below are based upon my detailed review of the manuscript. I hope you will be able to accept them all.

AR: thank you for your suggestions, we agreed with them all.

Ln 26: change ‘provide’ to ‘collect’

AR: changed

Ln 27: change ‘notably’ to ‘likely’

AR: accepted

Lns 31, 32, and throughout: change ‘breath rate’ to ‘breathing rate’

AR: accepted

Ln 31 – report here the observed breathing rate for the first animal

AR: added

Ln 32 – report here the observed breathing rate for the second animal

AR: added

Lns 36-37: change “By comparing all data it was found that” to “Our observations indicate that”

AR: changed

Ln 37: change “animal’s physical/physiological status” to “physical/physiological status of sperm whales” -- this is the key scientific contribution of this report.

AR: changed

AR: deleted

Ls 45 – change “Atlantic one” to “Atlantic population”

AR: changed

Ln 46 – change ‘this population’ to ‘the Mediterranean’

AR: changed

Ln 48 – insert “a” before “concerning matter”

AR: added

Ln 48 – interest ‘the’ before “international”

AR: added

Ln 65 – change ‘makes’ to ‘is’

AR: changed

Ln 74 – add ‘as sounds could not be ascribed to individual whales’ after ‘social unit’

AR: added

Ln 77 – add ‘production’ after ‘acoustic’

AR: added

Lns 79-80 – delete ‘intense’ before ‘stressful’

AR: added

Lns 80 – 86 delete these two sentences here, as they belong in the discussion. The text to this point provides adequate motivation and background.

AR: deleted

Ln 96 – change ‘shown’ to ‘had’

AR: changed

Ln 99 – change ‘Genre’ to ‘Sex’

AR: changed

Ln 105 – use past tense to refer to your specific study results, so change ‘are’ to ‘were’

AR: changed

Ln 106 – change ‘are described as follow’ to ‘were’

AR: changed

Ln 108 – change ‘specific phases for’ to ‘phases specific to’

AR: changed

Ln 115 – change ‘has been observed, which was described as’ to ‘was observed:’

AR: changed

Ln 117 – change ‘has been’ to ‘were’

AR: changed

Ln 123 – change ‘has been’ to ‘was’

AR: changed

Ln 129 – change ‘percentage’ to ‘rate’ (this is number per unit time). It should be reported as a number per unit time

AR: changed

Ln 136 – delete ‘mainly’

AR: done

Ln 149 – delete ‘for’

AR: done

Lns 149-150 change ‘for “single clicks” are intended sequences of clicks (ICI > 1 s), not organized in a defined structure, similar to ‘usual click’ described in literature [39]’ to “single clicks” were scored for sequences of clicks (ICI > 1 s) that were not organized in a defined structure, as described for ‘usual clicks’ [39]’

AR: changed

Ln 154 – delete ‘post-hoc’

AR: done

Ln 172 – state here the date the second whale was sighted

AR: done

Ln 176 – add ‘for small cetaceans’ after ‘recommended’

AR: added

Ln 192 – delete ‘of which’

AR: deleted

Ln 193 and Figure 4 – the methods describe this as the number of events divided by the total number of sessions. Therefore, this is a rate. The Y-axes should be number of events per unit time.

AR: changed

Ln 202 – add “the” before “post-rescue”

AR: added

Ln 205 – add ‘remained attached’ after ‘net’

AR: added

Fig 5 legend or Y-axis must state what is the number – ie “breaths/minute”

AR: added in the legend

Ln 219 – add ‘bin’ after ‘minute’.

AR: added

AR: thank you for the suggestion, we added ‘bin’ after ‘minute’

Ln 238 – change ‘are’ to ‘were’

AR: changed

Ln 241 – Delete “The first part of dataset included 56 minutes of acoustic recordings that were analysed for” and add ‘were analysed’ after “(18 July)”

AR: delete the first phrase and added the second

Ln 244 change ‘differed in’ to ‘differed between’

AR: changed

Ln 254 – delete ‘Whereas, ‘

AR: done

AR: changed

Ln 272 – state the sample size for this KW test.

AR: added

Ln 274 – change ‘first one’ to ‘first whale’

AR: changed

Ln 282 – change ‘has been’ to ‘were’

AR: changed

Ln 293 – change ‘higher trains duration’ to ‘higher train duration’

AR: changed

Lns 294-297. Specify the samples sizes used for all statistical tests.

AR: Done

Ln 303 – change ‘observed’ to ‘noted’

AR: changed

Ln 316 – change ‘smaller’ to ‘lower’

AR: changed

Fig 9 legend – Change “Coda types spectrograms” to “Spectrograms of coda types”

AR: changed

Ln 326 – change “3-clicks” to “3-click”

AR: changed

Ln 331 – change ‘a stressed’ to ‘active’

AR: changed

Ln 336 – change “pattern, especially on acoustic’ to “patterns, including acoustic”

AR: changed

Ln 338 – change “outputs” to “resulting observations”

AR: changed

Ln 345 – change “brought to free” to “successfully freed”

AR: changed

Ln 347 – change ‘run away’ to ‘swim away’

AR: changed

Ln 348 change “whales’s” to “whales’”

AR: changed

Ln 363 – add “The” before ‘First whale”

AR: added

Ln 364 – add “The” before “second whale”, and add “the” before “first” on the same line

AR: added

Ln 365 – change “to the hypothesis” to “with the hypothesis”

AR: changed

Ln 386 – change “resembling” to “resembled”

AR: changed

Ln 387 – change “a foraging behaviour” to “echolocation-based foraging”

AR: changed

Ln 389 – change ‘are very low’ to ‘were very low’

AR: changed

Ln 394 – change “are used” to “were used”

AR: changed

Ln 395 – delete “eventual”

AR: deleted

Ln 396 – change “do not fit” to “did not fit”

AR: changed

Ln 399 – change ‘in accordance with the stress level’ to ‘in accordance with the activity level’

AR: changed

Ln 401 -change “triggered by high-stress” to “during high activity”

AR: changed

Ln 409 – change “sight” to “encounter” both times.

AR: changed both

Ln 414 – use past tense. Change “are” to “were” and “share” to “shared”

AR: changed

Ln 415 – change “are” to “were”

AR: changed

Ln 416 – change “stressful” to “entanglement”

AR: changed

Ln 418 – change ‘are definitely’ to ‘were definitely’

AR: changed

Ln 421 – change ‘show’ to ‘had’

AR: changed

Ln 423 – add “were” before “operating”

AR: added

Ln 425 – change “to high” to “with high”

AR: changed

Ln 434 – change ‘enough’ to ‘sufficient’ and change “meaning” to “function”

AR: changed

Ln 437 – change “have known” to “are known”

AR: changed

Ln 449 – change “are” to “were”

AR: changed

Ln 453 – change “are more” to “were more”

AR: changed

Ln 460 – change “Orchinus” to “Orcinus”

AR: changed

Ln 461 – change “heard” to “produced”

AR: changed

AR: We agreed with your correction and we changed ‘is a first attempt’ with ‘is proposing’.

Ln 484 – delete “several” before “boats”

AR: deleted

Ln 508 – change to “Acknowledgements”

AR: changed

Ln 518 – change “any ethics statement is” to “no ethics statement is required”

AR: changed

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(20.6KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0250888.r005

Decision Letter 2

Patrick J O Miller

16 Apr 2021

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

PONE-D-20-40631R2

Dear Dr. Blasi,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Patrick J. O. Miller

Academic Editor

PLOS ONE

PLoS One. doi: 10.1371/journal.pone.0250888.r006

Acceptance letter

Patrick J O Miller

20 Apr 2021

PONE-D-20-40631R2

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

Dear Dr. Blasi:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Patrick J. O. Miller

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(49.9KB, docx)}

Attachment

Submitted filename: Response to Reviewers.docx

Click here for additional data file.^{(20.6KB, docx)}

Data Availability Statement

All relevant data are within the manuscript.

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PERMALINK

Behaviour and vocalizations of two sperm whales (Physeter macrocephalus) entangled in illegal driftnets in the Mediterranean Sea

Monica Francesca Blasi

Valentina Caserta

Chiara Bruno

Perla Salzeri

Agata Irene Di Paola

Alessandro Lucchetti

Roles

Abstract

Introduction

Materials and methods

Fig 1. Map of the Aeolian Archipelago.

Fig 2. Disentanglement phases for the first whale.

Fig 3. Disentanglement phases for the second whale.

Results

Entanglement events and rescue operations

Behavioural data

Fig 4. Rate (%) of each behavioural display in different phases.

Breathing pattern and diving time

Fig 5. Breathing rate (breaths per minute bin) trend, surface or diving behaviour, and vocalization recorded.

Fig 6. Mean breath/minute in each phase comparison.

Fig 7. Duration (minutes) of each dive (from D1-D15) for the second whale.

Acoustic behaviour

Table 1. Each sound emission type temporal and physical parameters.

Single clicks

Creaks

Fig 8. ICI (s) for each creak series in both whales.

Codas

Fig 9. Spectrograms of coda types and related inner-coda ICIs (s).

Discussion

Recommendations

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Patrick J O Miller

Roles

Author response to Decision Letter 0

Decision Letter 1

Patrick J O Miller

Roles

Author response to Decision Letter 1

Decision Letter 2

Patrick J O Miller

Roles

Acceptance letter

Patrick J O Miller

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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