Prey capture attempts can be detected in Steller sea lions and other marine predators using accelerometers

With technical advances in wildlife telemetry, the study of cryptic predators' responses to prey distribution has been revolutionised. In the case of marine predators, high resolution tagging devices have been developed recently to collect precise diving datasets covering extended periods of time. In this study, we investigated changes in the horizontal movements and diving patterns of a marine predator, the southern elephant seal, at fine temporal and spatial scales. Satellite tracking data collected for 9 seals were processed with switching state-space models. Seal body condition, as a proxy for foraging success, was estimated through changes in drift rate from Time Depth Recorder (TDR) data. We identified (1) statistically distinct behavioural modes from the tracking data (intensive vs. extensive foraging modes) and (2) distinct dive classes from the TDR diving data (drift, exploratory, shallow active and deep active dives). Active dives, associated with vertical foraging and chasing, were more numerous when the seals were in intensive foraging mode. Improved body condition and mass gain of seals were also associated with the intensive foraging mode and, within the vertical dimension, with sets of highly active dives. In conclusion, proportions of dive classes varied according to seals' horizontal behaviour. Intensive foraging detected from surface tracking data is a good predictor of diving activity and foraging success occurring in the vertical dimension.

Section: Methodological Perspectivesmentioning

confidence: 99%

Horizontal and vertical movements as predictors of foraging success in a marine predator

Dragon¹,

Bar-Hen²,

Monestiez³

et al. 2012

“…In the present study, the diving depth is defined as the mean depth during the bottom phase of the dive. Data from the accelerometer were processed according to Viviant et al (2010) and Gallon et al (2013) using custom-written MATLAB code (available on request). Identifying individual feeding events from the accelerometry data was performed according to the following procedures.…”

Section: Data Processing and Analysismentioning

confidence: 99%

“…External loggers such as the Inter-Mandibular Angle Sensor (IMASEN) record the mouth-opening angle of predators (Wilson et al 2002), but are sometimes difficult to apply on animals with flexible lips (Ropert-Coudert et al 2004, Liebsch et al 2007. Recent studies in free-ranging diving pinnipeds have overcome this methodological issue by using head-or jaw-mounted accelerometers to detect prey encounter events (PEEs) (Suzuki et al 2009, Naito et al 2010, 2013, Viviant et al 2010, Gallon et al 2013, Iwata et al 2012). This has enabled investigations into fine-scale temporal and spatial changes in the foraging of an increasing number of pinniped species, including the southern elephant seal Mirounga leonina (SES hereafter) − the largest and deepest-diving pinniped.…”

Section: Introductionmentioning

confidence: 99%

Southern elephant seal foraging success in relation to temperature and light conditions: insight into prey distribution

Guinet¹,

Vacquié‐Garcia²,

Picard³

et al. 2014

102

131

The distribution of southern elephant seal Mirounga leonina prey encounter events (PEEs) was investigated from the foraging behaviour of 29 post-breeding females simultaneously equipped with a satellite tag, a time−depth recorder and a head-mounted accelerometer. Seal diving depth and PEE were related to water temperature at 200 m (T 200 ), and light level at the surface (L 0 ) and at depth. Approximately half (49%) of all dives were located in waters encompassed between the southern Antarctic Circumpolar Current Front and the Polar Front. Seals dived significantly deeper during the day than at night. Diving and PEE depth increased with increasing T 200 and for a given T 200 according to L 0 and the percentage of surface light reaching 150 m. On average, 540 PEEs per day were recorded. Seals exhibited more PEEs per unit of time spent diving during the twilight period compared with at night, and were least successful during daylight hours. Elephant seals forage in T 200 ranging between −1 and 13°C; however, few PEEs were recorded at depths shallower than 400−500 m at night when the T 200 exceeded 8°C. The diet of female Kerguelen elephant seals appears to be dominated by myctophids (lanternfish), and according to the average mass of their most likely myctophid prey (9 g, Electrona calsbergi and E. antarctica; 30 g Gymnoscopelus nicholsi and G. piabilis), we estimate that seals consumed 4.8−16.1 kg of fish daily. Despite lower catch rates in warmer waters, no relationship was found between the mean T 200 at the scale of the foraging trip and daily or absolute mass gain, suggesting that elephant seals are compensating for lower catch rates by consuming larger/richer prey items in those waters.

“…The recent development of other technologies, particularly oesophageal and stomach temperature sensors (Wilson et al 1992), Hall sensors or accelerometers (Wilson et al 2002, Suzuki et al 2009, Viviant et al 2010, as well as video cameras (Bowen et al 2002, Davis et al 2003, is leading to a new stage in the understanding of successful foraging behaviour of marine predators. Indeed, these loggers are focused on measuring prey capture attempts (PCAs), which is currently considered as the best proxy for foraging success (see Guinet et al 2014 where prey encounter events [PEE] correspond to PCA).…”

Section: Introductionmentioning

confidence: 99%

Predicting prey capture rates of southern elephant seals from track and dive parameters

Vacquié‐Garcia¹,

Guinet²,

Dragon³

et al. 2015

In the marine environment, track and dive parameter data (obtained using Argos or GPS tags and time-depth recorders) are commonly used to provide proxies for foraging behaviour of marine predators. However, their accuracy is rarely assessed. Recently, the addition of headmounted accelerometers has allowed for detection of prey capture attempts (PCAs) at sea, allowing for more accurate estimations of foraging behaviour. Despite increased numbers of such devices being deployed, their use is still marginal compared with other tools which measure track and dive parameters. The objectives of our study were (1) to identify the most relevant combination of tracking and diving metrics in predicting the frequency of PCAs in female southern elephant seals Mirounga leonina from the Kerguelen Islands, and (2) to apply it to a broader range of individuals for which only tracking and diving data were available. The results of our models were consistent with the optimal foraging theory as well as the optimal diving theory. The model with the best predictive performance was the one that combined both tracking and diving information. However, most of the variability in the number of PCAs could be solely explained by changes in the diving behaviour of seals. Finally, we used the best predictive model on 20 individuals, which had not been fitted with accelerometers, to determine their main foraging zones. The behavioural indicators established in this study constitute a useful ecological tool for population monitoring and conservation purposes.