Diving deeper into individual foraging specializations of a large marine predator, the southern sea lion.
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.
Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Warrnambool, 3280, Australia. al_baylis@yahoo.com.au.|South Atlantic Environmental Research Institute, Stanley, FIQQ1ZZ, Falkland Islands. al_baylis@yahoo.com.au.|Falklands Conservation, Ross Road, Stanley, FIQQ1ZZ, Falkland Islands. al_baylis@yahoo.com.au.
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AM
Baylis
Department of Ocean Sciences, University of California, Santa Cruz, CA, 95060, USA.|Department of Fisheries and Wildlife, Oregon State University, Hatfield Marine Science Center, Newport, OR, 97365, USA.
R A
RA
Orben
Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Warrnambool, 3280, Australia.
J P Y
JP
Arnould
Falklands Conservation, Ross Road, Stanley, FIQQ1ZZ, Falkland Islands.
K
K
Peters
Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Warrnambool, 3280, Australia.
T
T
Knox
Department of Ocean Sciences, University of California, Santa Cruz, CA, 95060, USA.
D P
DP
Costa
British Antarctic Survey NERC, High Cross, Madingley Road, Cambridge, CB3 0ET, UK.
I J
IJ
Staniland
D000818:Animals; D004242:Diving; D004463:Ecology; D017753:Ecosystem; D019432:Falkland Islands; D005247:Feeding Behavior; D005260:Female; D011157:Population Dynamics; D011235:Predatory Behavior; D046070:Sea Lions / Q000502:physiology*
Dietary specialization; Habitat selection; Hidden Markov models; South American sea lions; State-space models