Water column use and forage strategies of female southern elephant seals from Marion Island |
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Authors: | Trevor McIntyre Horst Bornemann Joachim Plötz Cheryl A Tosh Marthán N Bester |
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Institution: | (1) Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002, South Africa;(2) Alfred Wegener Institute for Polar and Marine Research, Postfach 120161, 27515 Bremerhaven, Germany |
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Abstract: | The at-sea behaviour of marine top predators provides valuable insights into the distribution of prey species and strategies
used by predators to exploit patchily distributed resources. We describe the water column usage and dive strategies of female
southern elephant seals from Marion Island tracked between 2004 and 2008. Dives representing increases in forage effort were
identified using a method that combines dive type analyses and the calculation of relative amounts of time that animals spend
in the bottom phases of dives. Results from this analysis indicate that female elephant seals from Marion Island tend to display
lower levels of forage effort closer to the island and display intensive opportunistic forage bouts that occur at a minimum
distance of approximately 215 km from the island. Females from Marion Island dived deeper and for longer periods of time,
compared to females from other populations. Most animals displayed positive diel vertical migration, evidently foraging pelagically
on vertically migrating prey. A few animals displayed periods of reverse (negative) diel vertical migration, however, diving
to deeper depths at night, compared to daytime. This behaviour is difficult to explain and prey species targeted during such
periods unknown. Our results illustrate plasticity in foraging behaviour of southern elephant seals, as well as inter-population
differences in forage strategies. |
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