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

[摘要] ABSTRACT: 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 (T₂₀₀), and light level at the surface (L₀) 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 T₂₀₀ and for a given T₂₀₀ according to L₀ 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 T₂₀₀ ranging between -1 and 13°C; however, few PEEs were recorded at depths shallower than 400-500 m at night when the T₂₀₀ 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 T₂₀₀ 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.

[学科分类] 海洋学与技术

[关键词] Southern elephant seals;Foraging success;Light;Temperature;Diving behaviour;Prey