Abstract
Despite global declines in the abundance of marine predators, knowledge of foraging ecology, necessary to predict the ecological consequences of large changes in marine predator abundance, remains enigmatic for many species. Given that populations suffering severe declines are of conservation concern, we examined the foraging ecology of southern sea lions (SSL) (Otaria flavescens)—one of the least studied otariids (fur seal and sea lions)—which have declined by over 90 % at the Falkland Islands since the 1930s. Using a combination of biologging devices and stable isotope analysis of vibrissae, we redress major gaps in the knowledge of SSL ecology and quantify patterns of individual specialization. Specifically, we revealed two discrete foraging strategies, these being inshore (coastal) and offshore (outer Patagonian Shelf). The majority of adult female SSL (72 % or n = 21 of 29 SSL) foraged offshore. Adult female SSL that foraged offshore travelled further (92 ± 20 vs. 10 ± 4 km) and dived deeper (75 ± 23 vs. 21 ± 8 m) when compared to those that foraged inshore. Stable isotope analysis revealed long-term fidelity (years) to these discrete foraging habitats. In addition, we found further specialization within the offshore group, with adult female SSL separated into two clusters on the basis of benthic or mixed (benthic and pelagic) dive behavior (benthic dive proportion was 76 ± 9 vs. 51 ± 8 %, respectively). We suggest that foraging specialization in depleted populations such as SSL breeding at the Falkland Islands, are influenced by foraging site fidelity, and could be independent of intraspecific competition. Finally, the behavioral differences we describe are crucial to understanding population-level dynamics, impediments to population recovery, and threats to population persistence.
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Acknowledgments
For facilitating this research, we thank Rincon Grande farm, P Brickle, R Cordiero, C Dockrill, J Fenton, and N Rendell. AMMB and IJS received funding from the Darwin Initiative and Project AWARE for the 2011 field season. AMMB received funding from the Shackleton Scholarship Fund (Centenary Award), Rufford Small Grants, Sea World and Busch Gardens Conservation Fund, Joint Nature Conservation Council and the Falkland Islands Government for subsequent field seasons. DPC was supported by funding through the Office of Naval Research (N00014-13-1-0134). Research was conducted under permits R14/2011, R14/2013 and R14/2014 issued by the Falkland Islands Government to AMMB and the United States National Marine Fisheries Permit 17952 issued to DPC. Four anonymous reviewers improved earlier drafts of the paper.
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AMMB and IJS conceived the study and analysed the data. AMMB and RAO led the field work, with contributions from all authors. AMMB wrote the paper, with contributions from all authors.
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Baylis, A.M.M., Orben, R.A., Arnould, J.P.Y. et al. Diving deeper into individual foraging specializations of a large marine predator, the southern sea lion. Oecologia 179, 1053–1065 (2015). https://doi.org/10.1007/s00442-015-3421-4
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DOI: https://doi.org/10.1007/s00442-015-3421-4