Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean
Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean
Recent pup population estimates of sympatric Subantarctic (Arctocephalus tropicalis) and Antarctic fur seals (A. gazella) at Marion Island are presented. Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007–2015) were analyzed using a hierarchical Bayesian model. The pup population declined by 46% (95% credible interval CI: 43%–48%) between 2004 (mean = 15,260, CI: 14,447–16,169 pups) and 2013 (mean = 8,312, CI: 7,983–8,697), mirrored by a 58%–60% decline at rookeries counted annually (2007–2015). Population decline was highest at high-density west and north coast rookeries, despite negligible change in female attendance patterns, pup mortality or median pupping date over the previous 25 yr. A better understanding of foraging behavior and its effects on reproductive success and survival in this A. tropicalis population is needed before we can attribute population decline to any external factors. In contrast, total island counts of A. gazella pups in 2007, 2010, and 2013, suggest that this population is still increasing although the annual intrinsic rate of population growth decreased from 17.0% (1995–2004, 744 pups) to 4.0% (2010–2013, 1,553 pups). The slowed growth of A. gazella is likely the result of saturation at the main rookery.
Antarctic fur seal, Arctocephalus, count, density, detection probability, hierarchical Bayesian model, Marion Island, population estimate, Subantarctic fur seal, sympatry
960-982
Wege, Mia
d5c48d5b-9587-45e3-be59-273d1b59f938
Etienne, Marie Pierre
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Chris Oosthuizen, W.
c47dad12-f162-48e4-991e-9629439fba1c
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Bester, Marthán N.
41dd4579-d0bb-430f-9044-9d98a55d548c
de Bruyn, P. J.Nico
3257867f-eda3-4ddf-baa3-aaf692de19bb
1 July 2016
Wege, Mia
d5c48d5b-9587-45e3-be59-273d1b59f938
Etienne, Marie Pierre
00bf2fdb-3b6b-44d0-8355-075f47d3ed54
Chris Oosthuizen, W.
c47dad12-f162-48e4-991e-9629439fba1c
Reisinger, Ryan R.
4eaf9440-48e5-41fa-853f-d46457e5444e
Bester, Marthán N.
41dd4579-d0bb-430f-9044-9d98a55d548c
de Bruyn, P. J.Nico
3257867f-eda3-4ddf-baa3-aaf692de19bb
Wege, Mia, Etienne, Marie Pierre, Chris Oosthuizen, W., Reisinger, Ryan R., Bester, Marthán N. and de Bruyn, P. J.Nico
(2016)
Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean.
Marine Mammal Science, 32 (3), .
(doi:10.1111/mms.12306).
Abstract
Recent pup population estimates of sympatric Subantarctic (Arctocephalus tropicalis) and Antarctic fur seals (A. gazella) at Marion Island are presented. Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007–2015) were analyzed using a hierarchical Bayesian model. The pup population declined by 46% (95% credible interval CI: 43%–48%) between 2004 (mean = 15,260, CI: 14,447–16,169 pups) and 2013 (mean = 8,312, CI: 7,983–8,697), mirrored by a 58%–60% decline at rookeries counted annually (2007–2015). Population decline was highest at high-density west and north coast rookeries, despite negligible change in female attendance patterns, pup mortality or median pupping date over the previous 25 yr. A better understanding of foraging behavior and its effects on reproductive success and survival in this A. tropicalis population is needed before we can attribute population decline to any external factors. In contrast, total island counts of A. gazella pups in 2007, 2010, and 2013, suggest that this population is still increasing although the annual intrinsic rate of population growth decreased from 17.0% (1995–2004, 744 pups) to 4.0% (2010–2013, 1,553 pups). The slowed growth of A. gazella is likely the result of saturation at the main rookery.
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e-pub ahead of print date: 7 February 2016
Published date: 1 July 2016
Additional Information:
Funding Information:
The Department of Environmental Affairs supplied logistic support within the South African National Antarctic Programme. Financial support was provided by the Department of Science and Technology, through the National Research Foundation (NRF), in support of the Marion Island Marine Mammal Programme of the MRI. Greg Hofmeyr helped plan the 2013 total island count, and provided the 1995 and 2004 data as well as valuable insight. For assistance in the field we are grateful to Dawn Cory-Toussaint, Cheryl Tosh, Santjie du Toit, Mashudu Phalanndwa, Paul Visser, Derek van der Merwe, Hugh Purdon, Christiaan Conradie, Shadrack Podile, Thomas Mufanadzo, Johan van der Vyver, Nadia Hansa, Dani?l Kotz?, and Liezl Pretorius. All the above procedures have ethics clearance from the Animal Use and Care Committee (AUCC) of the Faculty of Natural and Agricultural Sciences, University of Pretoria, South Africa, under AUCC 040827-023. MNB benefitted from a Hanse-Wissenschaftskollege (Institute for Advanced Study) Fellowship during the final stages of preparing this manuscript.
Publisher Copyright:
© 2016 Society for Marine Mammalogy
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
Keywords:
Antarctic fur seal, Arctocephalus, count, density, detection probability, hierarchical Bayesian model, Marion Island, population estimate, Subantarctic fur seal, sympatry
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Local EPrints ID: 455016
URI: http://eprints.soton.ac.uk/id/eprint/455016
ISSN: 0824-0469
PURE UUID: 3ecdd5a4-44c5-4885-9342-8be8388808ab
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Date deposited: 03 Mar 2022 17:46
Last modified: 18 Mar 2024 04:03
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Contributors
Author:
Mia Wege
Author:
Marie Pierre Etienne
Author:
W. Chris Oosthuizen
Author:
Marthán N. Bester
Author:
P. J.Nico de Bruyn
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