Temporal foraging patterns of a top predator in the California Current Ecosystem revealed by stable isotope analysis

Naturally occurring climate regimes have been linked to changes in the fitness of top predators, notably through shifts in foraging patterns. When climate variability affects prey abundance and distribution, predators may show varied responses. The biotic and abiotic factors that influence predator-prey interactions and food web responses to variable climate conditions are not well understood. Examining these potential diet shifts is especially particularly important, as foraging dynamics can affect the reproductive success of top predators, many of which are of high conservation and management concern. The California sea lion (Zalophus californianus) is an ideal species to test the effects of climate-mediated impacts on top predators, as the population experiences mass mortality events that appear to coincide with climate shifts (e.g. El Nino Southern Oscillation [ENSO]). Archived tissues (1980-2015) from sea lions were sampled for stable isotope analysis to assess the trophic ecology of top predators in the California Current Ecosystem through a time series of bulk and amino acid-specific stable nitrogen (δ¹⁵N) values. Preliminary bulk δ¹⁵N values show no clear linear temporal trend from 1980-2015, but do show evidence of interannual variability, though these values do not appear to coincide with ENSO events. Future research includes compound-specific stable isotope analysis of amino acids to further resolve the mechanisms driving isotope patterns. Evaluating relationships between isotopic time series, environmental variability (e.g. ENSO events), and predator demographics may elucidate how climate-mediated shifts in food webs impact predator fitness and help predict climate change impacts on endangered or protected species.