Assessing the influence of traits and environment on the nutritional value of small pelagic species in the California Current
Creators: Krug-MacLeod, Alana M.
Publisher: name: University of Alberta Library
Year: 2024

<p>Marine food webs are increasingly disrupted by climate change, with implications for fisheries management. Understanding how changing ocean conditions are likely to affect the nutritional quality of prey species that predators depend on could assist with predicting population responses. Here we examine the extent to which environmental conditions and life history traits (body size, maturity status, and sex) are linked to variation in the nutritional traits of five small pelagic species varying in habitat use, feeding behaviour, size, and degree of importance as prey for top predators in the California Current Large Marine Ecosystem (CCLME). Boreal clubhook squid (Onychoteuthis borealijaponica), northern anchovy (Engraulis mordax), bigfin lanternfish (Symbolophorus californiensis), market squid (Doryteuthis opalescens), and pyrosomes (Pyrosoma atlanticum) were collected during two summer trawl surveys conducted by the National Oceanic and Atmospheric Administration in 2021. Specimens were processed for energy density (ED) via bomb calorimetry and for % lipid, % protein, and ED via proximate composition analysis, providing moisture values as well. Collection sites in the north and south regions of the CCLME varied in upwelling, sea surface temperature, and chlorophyll-a, allowing us to compare the nutritional values of specimens from two different environments. We used Bayesian multiple linear regression analysis with MCMC estimation to analyse the relationships among nutritional metrics, regions, and traits. Region of collection had little effect on the nutritional value of specimens—a result that was consistent across the species we sampled. Overall, pyrosomes had significantly lower ED and % lipid than the squid and fishes. Both ED and % lipid increased significantly with mass across the five species. However, species identity modulated this relationship; both ED and % lipid increased more slowly with increasing mass in boreal clubhook squid, market squid, and northern anchovy than in bigfin lanternfish. There was no overall effect of specimen mass on % protein, except in boreal clubhook squid, for which % protein increased with larger size. Pyrosomes and boreal clubhook squid had significantly lower % protein than all other species. As expected, there were significant, positive relationships between specimen body size and total energy (i.e., energy density multiplied by specimen mass), total lipid, and total protein. However, the strength of the relationships between size and total energy and total lipid increased with mass at a greater rate for the fishes than for the squids. We found that ED estimated from proximate composition was generally lower (especially for squids), but tightly correlated with ED from bomb calorimetry for all species (and our results provide conversion values that can be used for cross-study comparisons). The relationships we found between species, size, and nutritional metrics may provide generalizable insights useful for predicting foraging behaviour of top predators and for fisheries management as food webs adjust to climate change.</p>