Fat content and fatty acid composition of forage fish and invertebrates in Prince William Sound, Alaska: factors contributing to among and within species variability

Abstract

We determined the fat content and fatty acid composition of 26 species of fish and invertebrates (n = 1153) that are primary forage species of piscivorous seabirds and marine mammals in Prince William Sound (PWS), Alaska. Flatfish, shrimps and octopus had the lowest average fat contents (~1.0%), although some cods, as well as juvenile walleye pollock Theragra chalcogramma, Pacific herring Clupea harengus pallasi and pink salmon Oncorhynchus gorbuscha also ranged as low as 0.5 to 0.7% fat. The highest fat contents were found in eulachon Thaleichthys pacificus (25%), adult herring (21%) and the squid Berrytheuthis magister (5 to 13%). Within species, fat content varied mostly with season, but also with size. Fatty acid signatures generally distinguished forage species, with up to 95% of individuals correctly classified using either discriminant or classification and regression tree (CART) analyses. Discriminant plots provided insight into the relationships between fatty acid signatures of different species. Species with similar life histories and diets clustered closer together, while those with the greatest differences in ecology differed most in their fatty acid patterns. Within some species, changes in fatty acid signatures were apparent with increasing size and were consistent with known dietary shifts reported from stomach contents analyses. Furthermore, fatty acid signatures of Age 0 (yr) pollock and herring in PWS were consistent with previous stomach contents analysis that indicated annual differences in the timing of dietary changes from eating zooplankton to piscivory. Overall, when size/age classes were taken into account, species classification using fatty acid signatures was improved. Our findings have important implications for evaluating diets and food web interactions of fish stocks, as well as at higher trophic levels. Despite individual variation within species, our results indicate that fatty acid signatures accurately characterize forage species in this ecosystem, and consequently can be used to study and perhaps estimate the species composition of diets of their predators. KEY WORDS: Fatty acids · Forage fish · Food webs · Trophic interactionsResale or republication not permitted without written consent of the publisher

Nature in engineering for monitoring the oceans: comparison of the energetic costs of marine animals and AUVs

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Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiopssp.) provides access to a novel foraging niche

“…Values of 0 were set to 0.005%, as they could not be log transformed. This value was safely below the minimum detectable level [32].…”

“…Further, such samples are infrequently obtained or unfeasible due to their reliance on subject capture or mortality. In recent years, the analysis of fatty acids (FAs) has been shown to provide a powerful tool in diet studies [31][32][33]. The underlying premise is that FAs of consumed prey are deposited in a predictable manner into the adipose tissue of predators, thereby creating a unique profile of a number of FAs in various proportions, reflecting long-term diet [34].…”

Prey consumption and energy transfer by marine birds in the Gulf of Alaska

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