Table 1.
Indices used in analytical investigations of survival rates
| Variable name | Description |
|---|---|
| (a) Morphology and departure information (one value per individual) | |
| Sex | Sex of individual (male/female) |
| Departure date | Date each individual commenced the outward phase of first trip at sea following weaning |
| Departure weight | Departure weight (kg) estimated following Guinet (1994) as weight( t ) = weight( t −1) − (0.0048(weight( t −1)) + 0.3031), where t is time in days from tag deployment to pup departure |
| Departure drift rate | Departure drift rate (m/s) taken as an indicator of departure condition |
| (b) Horizontal movement metrics (time series at day scale) | |
| Max speed | The daily maximum current corrected speed (m/s) between two hourly filtered locations |
| Distance swam | The total current corrected distance swam (km) across a 24‐hr period |
| Current deviation | The daily mean difference between corrected swimming direction and the direction of ocean currents (o). Current deviations were rescaled so as bearings 180–360 ran from 180 (against ocean currents) to 0 (with ocean currents), which is consistent with those of original bearing 0–180 |
| (c) Acceleration and dive summaries (time series at dive scale) | |
| Dive depth | The maximum depth attained during a dive (m) |
| Dive duration | The total duration of a dive (s) |
| Scaled surface interval | The surface interval divided by the total duration of a dive (s) |
| PrCA rate | Total time spent in prey catch attempt (PrCA) behaviors (total time during which accelerations reflected “jerk”‐like movements) divided by total duration of a dive (s) |
| Scaled bottom duration | The total bottom duration divided by the total duration of a dive (s) |
| Swim effort | The total swimming effort (summed filtered accelerations associated with flipper movements across the lateral axis of the accelerometer) of the descent and ascent phases of a dive divided by the total corresponding durations of these phases (m/s3) |
| (d) Change in drift rate/body condition (time series at day scale) | |
| Drift rate change | Daily change in drift rate (m/s), between adjacent days. Positive values suggest an increase in seal buoyancy between days (likely through the acquisition of fat reserves) and negative values a decrease (either due to muscle development and/or loss of fat reserves) |
| (e) Environmental conditions (times series at day scale) | |
| Max wind | Daily maximum wind speed (m/s) encountered by an individual |
| Max wave height | Daily maximum wave height (m) encountered by an individual |
| Sea surface temperature | Daily mean surface temperature (°C) recorded by each individual's tag (at ~ 2‐3 m) |
| Max EKE | Daily maximum encountered eddy kinetic energy (EKE) taken as 0.5 () |
For each individual, these are representative of (a) morphology and departure information (one value), (b) horizontal movements (estimated daily), (c) fine‐scale acceleration‐ and dive‐based foraging behaviors (estimated for each dive transmitted), (d) drift rates/body condition (estimated daily), and (e) encountered environmental conditions (estimated daily)