Foraging strategies of a generalist marine predator inhabiting a dynamic environment
- 566 Downloads
Intraspecific variability is increasingly recognized as an important component of foraging behavior that can have implications for both population and community dynamics. We used an individual-level approach to describe the foraging behavior of an abundant, generalist predator that inhabits a dynamic marine ecosystem, focusing specifically on the different foraging strategies used by individuals in the same demographic group. We collected data on movements and diving behavior of adult female California sea lions (Zalophus californianus) across multiple foraging trips to sea. Sea lions (n = 35) used one of three foraging strategies that primarily differed in their oceanic zone and dive depth: a shallow, epipelagic strategy, a mixed epipelagic/benthic strategy, and a deep-diving strategy. Individuals varied in their degree of fidelity to a given strategy, with 66 % of sea lions using only one strategy on all or most of their foraging trips across the two-month tracking period. All foraging strategies were present in each of the sampling years, but there were inter-annual differences in the population-level importance of each strategy that may reflect changes in prey availability. Deep-diving sea lions traveled shorter distances and spent a greater proportion of time at the rookery than sea lions using the other two strategies, which may have energetic and reproductive implications. These results highlight the importance of an individual-based approach in describing the foraging behavior of female California sea lions and understanding how they respond to the seasonal and annual changes in prey availability that characterize the California Current System.
KeywordsIndividual variability Dive behavior Sea lion Zalophus californianus California Current
We thank Seth Newsome for helpful suggestions that improved the quality of this manuscript, the US. Navy for logistical support, and all of the field volunteers, without which this research would not have been possible. Data collection was part of the Tagging of Pelagic Predators (TOPP) project, and funded by the California Sea Grant Program, National Oceanographic Partnership Program, the Office of Naval Research, and the Moore, Packard, and Sloan Foundations. EAM was supported on a grant from the E & P Sound and Marine Life Joint Industry Programme (#22 07–23). Animal handling was permitted under NMFS permit #87-1593, 1851 and approved by the University of California Santa Cruz Institutional Animal Care and Use Committee.
Author contribution statement
EAM and DPC conceived the study, DPC, PWR, SES, CEK, and MF lead fieldwork, EAM and PWR analyzed the data, EAM wrote the manuscript, with contributions from all authors.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Buckley TW, Livingston PA (1997) Geographic variation in the diet of Pacific hake, with a note on cannibalism. Calif Coop Ocean Fish Investig Rep 38:53–62Google Scholar
- Carretta J V, Oleson EM, Weller DW, et al (2015) US Pacific marine mammal stock assessments: 2014. NOAA-TM-NMFS-SWFSC-549. doi: 10.7289/V5/TM-SWFSC-549
- Costa DP, Gentry RL (1986) Reproductive energetics of northern fur seals. In: Gentry RL, Kooyman GL (eds) Fur seals: maternal strategies on land and at sea. Princeton University Press, Princeton, New Jersey, pp 79–101Google Scholar
- Harris JD (2016) Estimation of an unobservable transition: from dependence to weaning in the California sea lion (Zalophus californianus). Master thesis, School of Environmental and Forest Sciences, University of Washington, Seattle, WA, USA. doi: 10.1017/CBO9781107415324.004
- Leising AW, Schroeder ID, Bograd SJ et al (2014) State of the California Current 2013-14: El Niño looming. Calif Coop Ocean Fish Investig Rep 55:51–87Google Scholar
- Livingston PA (1983) Food habitat of Pacific whiting, Merluccius productus, off the west coast of North America, 1967 and 1980. Fish Bull 81:629–636Google Scholar
- Lowry MS, Stewart BS, Heath CB et al (1988) Seasonal and annual variability in the diet of California sea lions Zalophus californianus at San Nicolas Island, California, 1981-86. Fish Bull 89:331–336Google Scholar
- Melin SR, Orr AJ, Harris JD, Delong RL (2012) California sea lions: an indicator for integrated ecosystem assessment of the California Current System. Calif Coop Ocean Fish Investig Rep 53:140–152Google Scholar
- Svanbäck R, Bolnick DI (2005) Intraspecific competition affects the strength of individual specialization: an optimal diet theory method. Evol Ecol Res 7:993–1012Google Scholar