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Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands

Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands
Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands
Antarctic (Arctocephalus gazella) and Subantarctic (A. tropicalis) fur seals are important predators in the Southern Ocean. Marion Island (southern Indian Ocean) hosts the largest sympatric breeding populations of these two species. Environmental and population changes here over two decades may have influenced their diet and trophic interactions. To quantify diet, we analysed prey remains in scat samples from Antarctic (661 scats) and Subantarctic (750 scats) fur seals collected at Marion Island (2006–2010). We assessed diet composition over time and calculated dietary overlap. The diet of both species was dominated by fish prey (98.2% and 99.4% of prey items), mainly myctophids. Antarctic fur seals consumed small numbers of penguins, cephalopods and crustaceans. In Subantarctic fur seal scats, crustaceans and cephalopods were rare and penguin remains were absent. The diets of the two species overlapped substantially (Pianka’s index = 0.98), however, small but significant differences in the relative proportions of prey were evident. Seasonal and annual diet changes suggest that their diet is similarly influenced by patterns of local prey availability and abundance. Despite substantial changes in the population size and trajectory of Antarctic and Subantarctic fur seals – which would be expected to influence trophic interactions between them – comparing our data to those from earlier studies (1989–2000) did not reveal significant long-term dietary changes in either species.
foraging, marine mammal, pinniped, Prey, scats, Southern Ocean
0800-0395
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Landman, Marietjie
8500bf6a-91ce-4525-a05e-40059d674c65
Mgibantaka, Nonkoliso
e7a426fa-9cb0-4f4d-8941-2f8197099c4d
Smale, Malcolm J.
55462834-c83b-4c96-b93e-f3c7b29a1df2
Bester, Marthán N.
41dd4579-d0bb-430f-9044-9d98a55d548c
De Bruyn, P. J.Nico
3257867f-eda3-4ddf-baa3-aaf692de19bb
Pistorius, Pierre A.
5a585272-2721-45dd-9384-56a05a477b36
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Landman, Marietjie
8500bf6a-91ce-4525-a05e-40059d674c65
Mgibantaka, Nonkoliso
e7a426fa-9cb0-4f4d-8941-2f8197099c4d
Smale, Malcolm J.
55462834-c83b-4c96-b93e-f3c7b29a1df2
Bester, Marthán N.
41dd4579-d0bb-430f-9044-9d98a55d548c
De Bruyn, P. J.Nico
3257867f-eda3-4ddf-baa3-aaf692de19bb
Pistorius, Pierre A.
5a585272-2721-45dd-9384-56a05a477b36

Reisinger, Ryan R., Landman, Marietjie, Mgibantaka, Nonkoliso, Smale, Malcolm J., Bester, Marthán N., De Bruyn, P. J.Nico and Pistorius, Pierre A. (2018) Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands. Polar Research, 37 (1), [1451142]. (doi:10.1080/17518369.2018.1451142).

Record type: Article

Abstract

Antarctic (Arctocephalus gazella) and Subantarctic (A. tropicalis) fur seals are important predators in the Southern Ocean. Marion Island (southern Indian Ocean) hosts the largest sympatric breeding populations of these two species. Environmental and population changes here over two decades may have influenced their diet and trophic interactions. To quantify diet, we analysed prey remains in scat samples from Antarctic (661 scats) and Subantarctic (750 scats) fur seals collected at Marion Island (2006–2010). We assessed diet composition over time and calculated dietary overlap. The diet of both species was dominated by fish prey (98.2% and 99.4% of prey items), mainly myctophids. Antarctic fur seals consumed small numbers of penguins, cephalopods and crustaceans. In Subantarctic fur seal scats, crustaceans and cephalopods were rare and penguin remains were absent. The diets of the two species overlapped substantially (Pianka’s index = 0.98), however, small but significant differences in the relative proportions of prey were evident. Seasonal and annual diet changes suggest that their diet is similarly influenced by patterns of local prey availability and abundance. Despite substantial changes in the population size and trajectory of Antarctic and Subantarctic fur seals – which would be expected to influence trophic interactions between them – comparing our data to those from earlier studies (1989–2000) did not reveal significant long-term dietary changes in either species.

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Published date: 20 April 2018
Keywords: foraging, marine mammal, pinniped, Prey, scats, Southern Ocean

Identifiers

Local EPrints ID: 455442
URI: http://eprints.soton.ac.uk/id/eprint/455442
ISSN: 0800-0395
PURE UUID: 99250602-0ba2-43f9-af9e-370133ec8f5f
ORCID for Ryan R. Reisinger: ORCID iD orcid.org/0000-0002-8933-6875

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Date deposited: 21 Mar 2022 17:55
Last modified: 18 Mar 2024 04:03

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Contributors

Author: Marietjie Landman
Author: Nonkoliso Mgibantaka
Author: Malcolm J. Smale
Author: Marthán N. Bester
Author: P. J.Nico De Bruyn
Author: Pierre A. Pistorius

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