Effects of Body Size and Environmental Region on the Nutritional Value of Small Pelagic Species in the California Current

ABSTRACT We evaluated the effects of regional environment and body size on the nutritional traits of five small pelagic species differing in habitat use, feeding behavior, and importance as prey for top predators in the California Current Large Marine Ecosystem (CCLME). Northern anchovy ( Engraulis mordax ), bigfin lanternfish ( Symbolophorus californiensis ), market squid ( Doryteuthis opalescens ), and boreal clubhook squid ( Onychoteuthis borealijaponica ) were collected in the summer of 2021 in the northern and southern CCLME. Energy density (ED), lipid, and protein content (% wet weight) were calculated for each specimen via bomb calorimetry and proximate composition analysis. Energy values from the two methods were highly correlated. Bayesian linear modeling revealed that while environmental conditions (sea surface temperature, chlorophyll‐ a , and upwelling) differed significantly between northern and southern CCLME, nutritional value did not vary significantly by region—an effect that was consistent across species. Body size affected both mass‐specific and whole specimen nutritional value, but the direction and magnitude of the relationship varied by species. While ED and % lipid increased rapidly with size in bigfin lanternfish and moderately with size in boreal clubhook squid, it was relatively consistent across size for anchovy and market squid. Fishes were more variable in ED and % lipid than squids, while % protein was highly variable across all specimens and increased significantly with size only in boreal clubhook squid. Our results highlight the importance of assessing drivers of prey quality to predicting predator foraging and nutrient flows under climate change.