Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean

• 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), AgroParisTech-Institut National de la Recherche Agronomique (INRA), 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: Arctocephalus; count; density; sympatry; detection probability; hierarchical Bayesian model; Marion Island; population estimate; Antarctic fur seal; Subantarctic fur seal; [SDV]Life Sciences [q-bio]; Antarctic; Southern Ocean; Antarc*; Antarctic Fur Seal; Antarctic Fur Seals
• Online Access: https://hal.archives-ouvertes.fr/hal-01531712; https://doi.org/10.1111/mms.12306

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 Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007-2015) were analyzed using a hierarchical Bayesian model.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.