Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean
Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean
Diet seems to be a key factor driving diversity and isolation among killer whale populations. Killer whales at Marion Island, Southern Ocean, have been observed preying on seals and penguins but are also know to depredate Patagonian toothfish from longline fishing vessels. However, their diet is poorly known especially when they occur offshore. We analysed carbon and nitrogen stable isotope ratios in 32 skin samples collected from 24 killer whales belonging to 8 social units. Adult males showed higher δ15N values than adult females or subadults, indicating that they occupy a higher relative trophic level. There were no significant differences in δ13C among social units, but δ15N differed significantly and 2 individuals from social units which have been observed depredating Patagonian toothfish had higher δ15N values. The inshore presence of killer whales at Marion Island was a significant predictor of δ13C values, but not of δ15N values. This suggests some foraging north of Marion Island, potentially on lower trophic level prey. We also analysed tissue samples from seal, penguin and Patagonian toothfish prey and used available values for Antarctic fur seals. Results show that killer whales around Marion Island are apex predators, but that they do not feed exclusively on other high trophic level predators such as elephant seals, fur seals, and Patagonian toothfish. Killer whales had δ15N values similar to those of Pata-gonian toothfish and adult male elephant seals, implying that the diet of killer whales at Marion Island includes some lower trophic level prey such as cephalopods or fishes.
Carbon, Foraging, Nitrogen, Predator, Stable isotopes, Trophic level, δC, δN
263-274
Reisinger, Ryan R.
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Gröcke, Darren R.
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Lübcker, Nico
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McClymont, Erin L.
9caac44d-1f22-40a2-b1e0-b13704d067bc
Hoelzel, A. Rus
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Nico De Bruyn, P. J.
90bf3f93-34ab-40aa-98be-e5a5ada56565
10 May 2016
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Gröcke, Darren R.
d33af9f3-012b-4f01-9c8e-190cc474a341
Lübcker, Nico
4eca3c9f-052f-4cc2-9f86-2fbf7ee7de64
McClymont, Erin L.
9caac44d-1f22-40a2-b1e0-b13704d067bc
Hoelzel, A. Rus
b911b554-8bee-4c68-9cf4-62214d803e7f
Nico De Bruyn, P. J.
90bf3f93-34ab-40aa-98be-e5a5ada56565
Reisinger, Ryan R., Gröcke, Darren R., Lübcker, Nico, McClymont, Erin L., Hoelzel, A. Rus and Nico De Bruyn, P. J.
(2016)
Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean.
Marine Ecology Progress Series, 549, .
(doi:10.3354/meps11676).
Abstract
Diet seems to be a key factor driving diversity and isolation among killer whale populations. Killer whales at Marion Island, Southern Ocean, have been observed preying on seals and penguins but are also know to depredate Patagonian toothfish from longline fishing vessels. However, their diet is poorly known especially when they occur offshore. We analysed carbon and nitrogen stable isotope ratios in 32 skin samples collected from 24 killer whales belonging to 8 social units. Adult males showed higher δ15N values than adult females or subadults, indicating that they occupy a higher relative trophic level. There were no significant differences in δ13C among social units, but δ15N differed significantly and 2 individuals from social units which have been observed depredating Patagonian toothfish had higher δ15N values. The inshore presence of killer whales at Marion Island was a significant predictor of δ13C values, but not of δ15N values. This suggests some foraging north of Marion Island, potentially on lower trophic level prey. We also analysed tissue samples from seal, penguin and Patagonian toothfish prey and used available values for Antarctic fur seals. Results show that killer whales around Marion Island are apex predators, but that they do not feed exclusively on other high trophic level predators such as elephant seals, fur seals, and Patagonian toothfish. Killer whales had δ15N values similar to those of Pata-gonian toothfish and adult male elephant seals, implying that the diet of killer whales at Marion Island includes some lower trophic level prey such as cephalopods or fishes.
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Published date: 10 May 2016
Additional Information:
Funding Information:
Funding was provided by the National Research Foundation's (NRF) Thuthuka and South African National Antarctic programmes, the South African Department of Science and Technology through the NRF, the Mohamed bin Zayed Species Conservation Fund (Project number: 10251290) and the International Whaling Commission's Southern Ocean Research Partnership. The Department of Environmental Affairs provided logistical support at Marion Island.
Publisher Copyright:
© 2016 SAMS.
Copyright:
Copyright 2016 Elsevier B.V., All rights reserved.
Keywords:
Carbon, Foraging, Nitrogen, Predator, Stable isotopes, Trophic level, δC, δN
Identifiers
Local EPrints ID: 455015
URI: http://eprints.soton.ac.uk/id/eprint/455015
ISSN: 0171-8630
PURE UUID: 25fe02ac-0411-4042-a77e-176e6e7a0ce9
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Date deposited: 03 Mar 2022 17:46
Last modified: 18 Mar 2024 04:03
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Contributors
Author:
Darren R. Gröcke
Author:
Nico Lübcker
Author:
Erin L. McClymont
Author:
A. Rus Hoelzel
Author:
P. J. Nico De Bruyn
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