Abstract: California sea lions (Zalophus californianus) are often viewed as a sentinel species whose health can be affected by prevailing oceanographic conditions and environmental quality. For this reason, it has become increasingly important to study natural stressors and anthropogenic impacts that can lead to diminished health and survival among individuals of this coastal species. In this study, Z. californianus stranding records spanning 1983 to 2010 were used to first identify regional and seasonal fisheries interaction hotspots in California, and second, to examine how these hotspots might change under additional environmental stress induced by El Niño oceanographic conditions that can affect prey availability. Analyzing mean monthly fisheries interaction cases as an example of human-related stranding revealed that (1) the number of monthly fisheries interaction cases has risen significantly over time proportional to statewide abundance estimates; (2) cases were significantly higher in Monterey, Los Angeles, and Orange Counties; (3) cases peaked May through August; and (4) fisheries interactions were significantly greater during El Niño conditions throughout the state. These results indicated that over a 27-y period, California sea lion health was affected by oceanographic conditions and that anthropogenic impacts may be heightened in early summer following the weaning period when young animals learning to forage may be less successful in El Niño conditions. Spatially and temporally explicit data such as these can be useful in mapping marine mammal health and understanding the dynamic natural and anthropogenic landscapes in which they are a part.
Key Words: hotspots, California sea lion, Zalophus californianus, fisheries interactions, El Niño Southern Oscillation, California Current Ecosystem, stranding
Document Type: Research article
DOI: 10.1578/AM.39.3.2013.221
Page Numbers: 221-232

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