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. Author manuscript; available in PMC: 2021 Oct 21.
Published in final edited form as: Ann Ser Hist Nat. 2021;31(1):51–57. doi: 10.19233/ASHN.2021.08

Using Citizen Science to Detect Rare and Endangered Species: New Records of the Great White Shark Carcharodon Carcharias off the Libyan Coast

Patrick L Jambura 1, Julia Türtscher 1, Alessandro De maddalena 2, Ioannis Giovos 3, Jürgen Kriwet 4, Jamila Rizgalla 5, Sara AA Al mabruk 6
PMCID: PMC7611865  EMSID: EMS135982  PMID: 34690539

Abstract

The presence of the great white shark (Carcharodon carcharias) in the Mediterranean Sea is well documented, but encounters with this species are rare and all assumptions about its spatial and temporal distribution are heavily relying on anecdotal observations. To date, only one record off the Libyan coast has been reported, raising the question if this species is underreported in these waters or simply represents a rare occasional transient. We utilised citizen science-sourced data to document the presence of the great white shark off the Libyan coast, and found six additional records for this species from the period between 2017 and 2020. Our study points out the need for scientific monitoring of this species along the Libyan coast to facilitate the establishment of effective conservation plans to protect this critically endangered species.

Keywords: Elasmobranchii, cartilaginous fish, conservation biology, fisheries, social media, threatened species

Introduction

The great white shark Carcharodon carcharias (L., 1758) is, with a total length of at least six meters (Randall, 1973; Castro, 2012), one of the largest marine predators worldwide. This cosmopolitan species inhabits mainly temperate and subtropical waters, with adult individuals rarely entering tropical waters (Compagno, 2001). In the Mediterranean Sea, white sharks have been frequently reported from the Strait of Sicily (Storai et al., 2000; Ben Amor et al., 2020; Tiralongo et al., 2020), the Tyrrhenian Sea (Storai et al., 2000), the Gulf of Lions (De Maddalena & Zuffa, 2009), the Balearic Islands (Morey et al., 2003), the Adriatic Sea (De Maddalena, 2000; Soldo & Jardas, 2002), the Ionian Sea (Papaconstantinou, 2014), the Marmara Sea, including the Bosphorus Strait (Kabasakal, 2003, 2014, 2016), and the Aegean Sea (Kabasakal, 2014, 2016, 2019; Papaconstantinou, 2014). Based on the occurrence of neonates, small juveniles and pregnant females, the existence of two possible nursery areas has been proposed in the Mediterranean Sea, one in the Strait of Sicily, Central Mediterranean Sea (Fergusson, 1996; Saïdi et al., 2005; Bradaï & Saïdi, 2013) and another in Edremit Bay, northern Aegean Sea (Kabasakal, 2016, 2020a,b).

Molecular studies examining the genetic profile of white sharks via the mt-DNA control region have revealed the presence of an isolated Mediterranean population, which exhibits little genetic variability and only has limited genetic exchange with the Atlantic population (Gubili et al., 2011; 2015; Leone et al., 2020). This lack of genetic diversity coupled with little or no contemporary immigration from the Atlantic renders the Mediterranean population extraordinarily prone to extinction (Gubili et al., 2011; 2015). According to the IUCN Red List of Threatened Species, white sharks are declared globally vulnerable (VU; Rigby et al., 2019), while the Mediterranean population is listed as critically endangered (CR; Soldo et al., 2016). In an attempt to assess population trends and dynamics for white sharks in the Mediterranean, Moro et al. (2020) compiled a comprehensive database of 773 white shark records between 1860 and 2016 and found a 52–96% overall population decline in different Mediterranean sectors and a contraction in spatial distribution. It should be noted that encounters with white sharks in the Mediterranean Sea are usually rare and very sporadic in nature. Therefore, all hypotheses about distribution, migration patterns, parturition, and the conservation status of white sharks in the Mediterranean Sea rely on anecdotal observations, like historical captures and sighting data (Fergusson, 1996; De Maddalena & Heim, 2012; Boldrochhi et al., 2017; Moro et al., 2020). Due to insufficient fishery data for many shark species, especially rare ones (Damalas & Megalofonou, 2012; Cashion et al., 2019), and the absence of coordinated scientific surveys, citizen science has frequently been used to monitor the presence of rare shark species in the Mediterranean Sea (e.g., Giovos et al., 2019; Kabasakal & Bilecenoğlu, 2020; Jambura et al., 2021).

Landing almost 4.3 tonnes of chondrichthyan fishes in 2015, Libya is the leading country for chondrichthyan catches in the Mediterranean Sea (Jeffries, 2019). However, little is known about the presence of white sharks in Libyan waters and only a single record of a large female white shark off the Libyan coast does exist (Galaz & De Maddalena, 2004). Assessing the presence of white sharks in Libyan waters is, consequently, of utmost importance for future conservation planning of this iconic shark species. In our study, a systematic online search on popular social media platforms (i.e., Facebook, YouTube, Instagram, and Twitter) was conducted to document the presence of the great white shark C. carcharias along the Libyan coast and to augment our understanding of the distribution and ecology of this rare species in the Mediterranean Sea.

Material and Methods

Records of white shark C. carcharias off the Libyan coast were accumulated within the context of the citizen-science initiative “Monitoring Elasmobranchii in Libyan Waters”, which was conducted by “Marine Biology in Libya”. This programme puts a focus on the occurrence of chondrichthyan fishes in the Mediterranean Sea and applies a verified citizen science model, in which citizen-submitted observations are checked by experts (Gardiner et al., 2012). The records either came directly from fishermen reporting their catch, or through systematic online searches on social media platforms, namely Facebook, YouTube, Instagram, and Twitter using the Arabic keyword for great white shark (القرش الأبیض, “alqarsh al’abyad”) and shark (قرش, “qarash”; or كلب بحر, “kaleb baher”). Following the ethical code proposed by Monkman et al. (2018), all web scraping was performed responsibly to avoid compromising any personal data or images. All records had to be accompanied by photographic evidence confirming the identification of the reported species. Authenticity and originality of the images were checked with the Google automatic image recognition tool. Species identification was based on the following features: (1) heavily, long-snouted spindle-shaped body; (2) strong keels on caudal peduncle; (3) large first dorsal fin, very small second dorsal and anal fins; (4) lunate caudal fin; (5) large, flat, triangular, serrated teeth; (6) long gill slits; (7) black eyes; (8) sharp colour change from greyish dorsally to white ventrally; (9) pectoral fins with black tips on the ventral side (Ebert et al., 2013). Subsequent interviews were conducted with citizen scientists to confirm the reported data and obtain further information. If direct contact with the observer was not successful, the record was considered ambiguous and subsequently discarded. In addition to date and location, the following data were added to each record when possible: (1) time, (2) fishing method, (3) condition, (4) sex, (5) estimated total length (TLest), (6) weight (Tab. 1). Estimated total lengths were validated by comparing the shark with objects of known size in the photos. When applicable, ontogenetic stages were identified based on the total length following Boldrocchi et al. (2017): young of the year (YOY) (TL ≤ 1.75 m), juvenile (TL 1.75–3.0 m), subadult (♂TL 3.0–3.6 m; ♀TL 3.0–4.5m), adult (♂TL > 3.6 m; ♀TL > 4.5 m).

Tab. 1.

Observations of great white sharks (Carcharodon carcharias) reported from the Mediterranean Sea between 2017 and 2020. Abbreviation: YOY, young-of-year. *size and ontogenetic stage estimated by the observer.

Tab. 1: Opazovanja belih morskih volkov (Carcharodon carcharias), ki so bila v Sredozemskem morju dokumentirana v letih 2017-2020. Okrajšava: YOY, enoletni primerek. *velikost in ontogenetski stadij, ki ga je ocenil opazovalec.

Country Region Date Fishing type Condition Sex Ontogeny TL [cm] Weight [kg] Coordinates Source
Italy Lampedusa 23.05.2020 observation alive female adult 500 - - Tiralongo et al. (2020)
Libya Bouri field 29.07.201 7 observation alive - adult* 600* - 34.054444°N, 12.789972°E this study
Buerat 16.05.2018 gillnet dead female juvenile 230 135 31.399611°N, 15.736333°E this study
Brega 12.01.2020 observation dead male adult 520 - 30.3475°N, 19.441528°E this study
Daryanah 23.04.2020 observation alive - adult* 600* - 32.398306°N, 20.339444°E this study
Tripoli 21.09.2020 gillnet dead female YOY 140 - - this study
Gökçeada 04.11.2020 observation alive - adult* 600* - 32.959333°N, 13.1 67389°E this study
Turkey Gökçeada 01.2017 gillnet dead - juvenile 180 - - Kabasakal (2020a)
Altinoluk 04.2017 gillnet alive - YOY 160 - - Kabasakal (2020a)
Didim 04.06.2017 purse seine dead male juvenile 200 60 - Kabasakal et al. (2019)
Izmir 14.04.2018 gillnet dead female juvenile 180 - - Kabasakal et al. (2019)
Sousse 28.04.2020 drift longline dead female juvenile 232 90 35.016944°N, 12.186389°E Ben Amor et al. (2020)
Kumkale 08.06.2020 gillnet dead - YOY 155 - - Kabasakal (2020b)
Enez 14.06.2020 observation alive - juvenile 200 - - Kabasakal (2020b)
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Results

Between 2017 and 2020, six white sharks (C. carcharias) were reported off the Libyan coast, constituting 42.9% of all published records of this species in the entire Mediterranean Sea during the same period (Tab. 1). One record was from 2017, one from 2018, and four were from 2020. Half of the recorded white sharks were reported dead (n=3); two of them were caught in set gillnets and one was washed ashore (see cases 2, 3, and 5). Ontogenetic stage and sex could be determined for four and three individuals, respectively; two sharks were adults (one male, one of unknown sex) and two were juveniles (both female). A short description for each record is provided below.

Case 1: On 29 July 2017, a white shark was filmed from an oil platform while swimming near the surface in the Bouri Offshore Field, 120 km north of the Libyan coast, (34.054444°N, 12.789972°E; Figs. 1, 2A; Tab. 1). It was not possible to determine the sex or size of this specimen. The observer, however, estimated it to be 6 m long, and, therefore, likely an adult specimen.

Fig. 1.

Fig. 1

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Occurrence of the great white shark (Carcharodon carcharias) off the Libyan coast. Recent records (circle) were reported between 2017 and 2020, while the only previously published record (triangle) was reported in 2002. Detailed information about each observation is provided in Table 1.

Sl. 1: Pojavljanje belega morskega volka (Carcharodon carcharias) vzdolž libijske obale. Recentni podatki (krogci) izvirajo med leti 2017 in 2020, medtem ko je bil edini dokumentirani zapis o pojavljanju te vrste (trikotnik) objavljen leta 2002. Natančni podatki o vsakem od opazovanih primerov so navedeni v Tabeli 1.

Fig. 2. Reports of great white sharks (Carcharodon carcharias) observed off the Libyan coast between 2017 and 2020.

Fig. 2

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Detailed information about each observation is provided in Table 1. Photo credits: (A) Jamal Al hamali, (B) Archive Marine Biology in Libya Society, (C) Mohamed Ahmed Salah, (D) Kamal Zager, (E) Aimen Al jerbie.

Sl. 2:Pojavljanje morskega volka (Carcharodon carcharias) vzdolž libijske obale v obdobju med 2017 in 2020. Natančni podatki o vsakem od opazovanih primerov so navedeni v Tabeli 1. Avtorji fotografij: (A) Jamal Al hamali, (B) Archive Marine Biology in Libya Society, (C) Mohamed Ahmed Salah, (D) Kamal Zager,(E) Aimen Al jerbie.

Case 2: On 16 May 2018, a small white shark was caught in a gillnet near the village of Buerat, 84 km west of Sirte (31.399611°N, 15.736333°E; Figs. 1, 2B; Tab. 1). The shark was alive when captured, but was landed and sold at the local fish market. The fishermen identified it as a shortfin mako shark (Isurus oxyrinchus), however, the black tips on the ventral side of the pectoral fins and the flat triangular teeth clearly indicate it was a white shark. The specimen was a female measuring 2.3 m (total length, TL) and, therefore, a juvenile.

Case 3: On 12 January 2020, a large white shark was washed ashore near the town of Brega, 300 km east of Sirte (30.3475°N, 19.441528°E; Figs. 1, 2C; Tab. 1). No external injuries that would explain the cause of death could be detected. The specimen was a male with well developed claspers and measuring 5.2 m (TL). We, therefore, conclude that this specimen represented an adult individual.

Case 4: On 23 April 2020, a white shark was observed swimming near the surface following a small fishing vessel, which carried out blast fishing near the town of Daryanah, 32 km east of Benghazi (32.398306°N, 20.339444°E; Fig. 1; Tab. 1). The fishermen estimated the shark to be 6 m long. The video material, however, did not allow confirmation of this estimate. Although the shark was reported to be alive, at the end of the video sequence one of the fishermen threw dynamite towards the shark in order to chase it off and probably killed it.

Case 5: On 21 September 2020, a small white shark was caught in a set gillnet and landed in the Bab Albaher fish market in Tripoli (Figs 1, 2D; Tab. 1). The exact locality where this individual was caught could not be reconstructed. However, due to the ongoing civil war in Libya, fishing boats from Tripoli are not allowed to enter the Gulf of Sidra and are restricted to the area between the Libyan-Tunisian boundary to the west and the city of Misrata to the east. Therefore, it is certain that this individual was caught in the area around Tripoli. The shark was a female measuring 1.4 m. The presence or absence of an umbilical scar could not be verified because the whole ventral side of the shark was cut open. Nevertheless, the total length is well within the size category of young of year (YOY < 1.75 m) and, therefore, it is considered as such here. This record represents the southernmost occurrence of a YOY white shark in the Mediterranean Sea.

Case 6: On 4 November 2020, a white shark was observed in the proximity of two small fishing vessels near Tripoli (32.959333°N, 13.167389°E; Figs. 1, 2E; Tab. 1). The shark was swimming close to the surface and was accompanied by seven pilot fish (Naucrates ductor). The total length was estimated to be 6 m by the fishermen, but the video sequence did not allow confirmation of this estimate or identification of the sex of the specimen.

Discussion

The presence of white sharks in the Mediterranean Sea has been known since the Middle Ages (476–1453) but is documented solely based on anecdotal reports of rather rare encounters (De Maddalena & Heim, 2012; Boldrocchi et al., 2017). In the present paper, citizen science-sourced data from social media platforms was used to gain a more detailed insight into the occurrence, distribution, and ecology of this elusive species along the Libyan coast. The species was previously only reported from this region in a single record of an adult female shark caught in a tuna cage 55 miles off Tripoli (Galaz & De Maddalena, 2004). Our search resulted in six additional records reported over a relatively short period (between 2017 and 2020), indicating that this species might be more common in this area than previously thought. In a recent study, five specimens of C. carcharias were reported from the North East Aegean Sea, based on social media and internet sources (Kabasakal & Bilecenoğlu, 2020), further indicating the importance and potential of such data sources (and citizen science in general) for white shark research in the Mediterranean Sea.

Our results suggest that both immature and mature white sharks exploit the waters off the Libyan coast. The Central Mediterranean Sea is characterised by high biodiversity, especially in the area around the Strait of Sicily (Spanò & De Domenico, 2017), which is also an area displaying a high occurrence of white sharks (Fergusson, 1996; Boldrocchi et al., 2017). Fergusson (1996) proposed that this region was critical for the species’ reproduction and that the neritic waters of Sicily and Tunisia served as nursery areas, a hypothesis that has been supported by subsequent studies (e.g., Saïdi et al., 2005; Bradaï & Saïdi, 2013; Boldrocchi et al., 2017).

Our observations of a young of the year and a juvenile white shark along the Libyan coast represent the southernmost occurrence of immature individuals of this species in the Mediterranean Sea and suggest that the Central Mediterranean nursery area might not be restricted to Sicily and Tunisia but may extend as far south as Libya. This seems reasonable, as white sharks can inhabit vast nursery grounds with YOYs travelling up to 700 km within a month (Weng et al., 2007). The Gulf of Gabes, a frequently suggested nursery ground for white sharks (Saïdi et al., 2005; Bradaï & Saïdi, 2013), is situated ca. 350 km west of where the YOY reported here was landed. It should be noted that incidental captures of YOY and juvenile white sharks in Tunisia usually occur in winter and spring, with a peak in February, while no YOY or juvenile has been reported in September so far, when the specimen documented here was caught. Therefore, an eastwards movement of YOY and juvenile white sharks from their primary nursery area in the Gulf of Gabes cannot be excluded either. The juvenile specimen reported here was caught further east, ca. 700 km west of the Gulf of Gabes. Previously, juveniles were reported to travel greater distances than YOYs (Kabasakal, 2020a), further indicating that the Libyan coast might serve as an extension of the nursery ground of the Gulf of Gabes. More data, however, is needed to confirm this.

The great white shark C. carcharias is listed as an Appendix II species of the Convention on International Trade in Endangered Species (CITES) and is also included in the Barcelona Convention Annex II SPA/BD protocol. According to the Fisheries Commission for the Mediterranean Sea (GFCM), white sharks caught during fishing operations have to be released promptly and unharmed to the greatest extent possible. They cannot be retained on board, transferred, landed or sold (Recommendation GFCM/42/2018/2). Our study revealed that critically endangered white sharks are caught and sold in Libya, despite Libya being a member of the GFCM and, therefore, obliged to follow this recommendation. One of the main problems we identified when talking to fishermen about their records was that they were completely unaware of the presence of white sharks in their fishing area and usually mistook the reported specimens for shortfin makos (Isurus oxyrinchus). We therefore urge for the organisation of educational and awareness campaigns aimed at aiding fishermen in correctly identifying white sharks and informing them about the white shark’s conservation status and regulations that are in place to help this species recover in the Mediterranean Sea.

Acknowledgements

This study was carried out as part of the citizen science collaboration “The MECO (Mediterranean Elasmobranch Citizen Observations) Project”. We further want to thank Ali Embarak, Daw Haddoud, Moutaz Mohamed Ehshad, Aymen Al-jerbie, and a reporter who wants to stay anonymous for providing additional photographs and information about the records. We are very grateful to two anonymous reviewers for their comments on a previous version of this manuscript. This research was supported by the Austrian Science Fund (FWF): P 33820 to Jürgen Kriwet.

Contributor Information

Patrick L. Jambura, Email: patrick.jambura@gmail.com.

Alessandro De maddalena, Shark Museum, Cape Town 7995, South Africa.

Ioannis Giovos, iSea, Environmental Organization for the Preservation of the Aquatic Ecosystems, Thessaloniki 54645, Greece.

Jürgen Kriwet, University of Vienna, Department of Palaeontology, Vienna 1090, Austria.

Jamila Rizgalla, University of Tripoli, Faculty of Agriculture, Department of Aquaculture, Tripoli, Libya.

Sara A.A. Al mabruk, Higher institute of Science and Technology, Department of General Nursing Technology, Cyrene, Libya Marine Biology in Libya Society, El Bayda, Libya

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