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Predatory impact of killer whales on pinniped and penguin populations at the Subantarctic Prince Edward Islands: Fact and fiction

Predatory impact of killer whales on pinniped and penguin populations at the Subantarctic Prince Edward Islands: Fact and fiction
Predatory impact of killer whales on pinniped and penguin populations at the Subantarctic Prince Edward Islands: Fact and fiction

Killer whales are the oceans' apex predators and their potential effects on ecosystems have been demonstrated. In the Southern Ocean, the role of killer whale predation in population declines of southern elephant seals remains largely speculative. We aimed to assess whether top-down control of pinniped and penguin populations at the Subantarctic Prince Edward Islands (PEIs) is generally plausible using a simple process of elimination. Based on published data, we predicted the energetic ingestion requirements of adult male and female killer whales as 1394 and 1028MJday-1, respectively. Expanding these requirements to the 37 killer whales photographically identified at the PEIs, the population requires 40600MJday-1. Based on the energy density and mass data available, we predicted the energy content of available pinniped and penguin prey and calculated the rates at which killer whales would consume these prey in various scenarios. Penguins and Subantarctic fur seals are relatively insensitive to killer whale predation owing to their large population sizes (10000-100000s). Conversely, the smaller populations (100-1000s) of Antarctic fur seals and southern elephant seals are sensitive to predation, particularly the latter, as they have a high energy content (c. 2000-9000MJ). Populations of these seals are currently increasing or stable and we conclude that presently killer whale predation is not driving population declines, although they clearly have the potential for the regulation of these smaller populations. Thus, if population sizes were reduced by bottom-up processes, if killer whale diet shifted or if prey availability changed, top-down predation by killer whales could become significant. By eliminating the possibility of some predation scenarios, we are better able to concentrate future efforts on plausible predation effects.

Apex predator, Elephant seal, Fur seal, Orcinus orca, Penguin, Predator-prey interactions, Top-down control
0952-8369
1-10
Reisinger, R. R.
4eaf9440-48e5-41fa-853f-d46457e5444e
de Bruyn, P. J.N.
4239fc92-c272-4bad-a8ca-c5edf24fa933
Bester, M. N.
cde32f42-fedb-42c6-9a0e-b797259c1cac
Reisinger, R. R.
4eaf9440-48e5-41fa-853f-d46457e5444e
de Bruyn, P. J.N.
4239fc92-c272-4bad-a8ca-c5edf24fa933
Bester, M. N.
cde32f42-fedb-42c6-9a0e-b797259c1cac

Reisinger, R. R., de Bruyn, P. J.N. and Bester, M. N. (2011) Predatory impact of killer whales on pinniped and penguin populations at the Subantarctic Prince Edward Islands: Fact and fiction. Journal of Zoology, 285 (1), 1-10. (doi:10.1111/j.1469-7998.2011.00815.x).

Record type: Article

Abstract

Killer whales are the oceans' apex predators and their potential effects on ecosystems have been demonstrated. In the Southern Ocean, the role of killer whale predation in population declines of southern elephant seals remains largely speculative. We aimed to assess whether top-down control of pinniped and penguin populations at the Subantarctic Prince Edward Islands (PEIs) is generally plausible using a simple process of elimination. Based on published data, we predicted the energetic ingestion requirements of adult male and female killer whales as 1394 and 1028MJday-1, respectively. Expanding these requirements to the 37 killer whales photographically identified at the PEIs, the population requires 40600MJday-1. Based on the energy density and mass data available, we predicted the energy content of available pinniped and penguin prey and calculated the rates at which killer whales would consume these prey in various scenarios. Penguins and Subantarctic fur seals are relatively insensitive to killer whale predation owing to their large population sizes (10000-100000s). Conversely, the smaller populations (100-1000s) of Antarctic fur seals and southern elephant seals are sensitive to predation, particularly the latter, as they have a high energy content (c. 2000-9000MJ). Populations of these seals are currently increasing or stable and we conclude that presently killer whale predation is not driving population declines, although they clearly have the potential for the regulation of these smaller populations. Thus, if population sizes were reduced by bottom-up processes, if killer whale diet shifted or if prey availability changed, top-down predation by killer whales could become significant. By eliminating the possibility of some predation scenarios, we are better able to concentrate future efforts on plausible predation effects.

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More information

Published date: September 2011
Additional Information: Copyright: Copyright 2011 Elsevier B.V., All rights reserved.
Keywords: Apex predator, Elephant seal, Fur seal, Orcinus orca, Penguin, Predator-prey interactions, Top-down control

Identifiers

Local EPrints ID: 469007
URI: http://eprints.soton.ac.uk/id/eprint/469007
ISSN: 0952-8369
PURE UUID: ee5810bf-33df-4279-949c-147c1cc981d3
ORCID for R. R. Reisinger: ORCID iD orcid.org/0000-0002-8933-6875

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Date deposited: 05 Sep 2022 16:38
Last modified: 17 Mar 2024 04:08

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Contributors

Author: R. R. Reisinger ORCID iD
Author: P. J.N. de Bruyn
Author: M. N. Bester

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