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 Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets o...

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Bibliographic Details
Published in:Marine Mammal Science
Main Authors: Wege, Mia, Etienne, Marie-Pierre, Chris Oosthuizen, W., Reisinger, Ryan R., Bester, Marthán N., de Bruyn, P. J. Nico
Other Authors: University of Pretoria South Africa, Mathématiques et Informatique Appliquées (MIA-Paris), Institut National de la Recherche Agronomique (INRA)-AgroParisTech, Department of Science and Technology, through the National Research Foundation (NRF) Hanse-Wissenschaftskollege (Institute for Advanced Study)
Format: Article in Journal/Newspaper
Language:English
Published: HAL CCSD 2016
Subjects:
count
density
sympatry
detection probability
hierarchical Bayesian model
Marion Island
population estimate
Antarctic fur seal
Arctocephalus
Subantarctic fur seal
[SDV]Life Sciences [q-bio]
Antarctic
Southern Ocean
Antarc*
Antarctic Fur Seal
Antarctic Fur Seals
Online Access:https://hal.science/hal-01531712
https://doi.org/10.1111/mms.12306
Description
Summary: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 Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007-2015) were analyzed using a hierarchical Bayesian model.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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