Running Head. — Feeding Ecology of Ammodytes hexapterus

Abstract

Forage fish such as herring, surf perch and Pacific sand lance are a crucial link between lower and upper elements in the food chain, transferring dense energy and vitamin content from primary producers (phytoplankton) to higher trophic levels (piscivorous fishes, birds, and marine mammals). In this study we examined the feeding ecology and trophic role of A. hexapterus in the San Juan Archipelago. We collected data on mass, fork length, population structure, substrate, and stomach contents and used a chi-square test to examine whether or not there were differences in fullness and digestion as a function diel, tidal and seasonal cycles. Our results suggest that time of day has a significant influence on stomach fullness (X2 =16.01, P=0.042), but not digestion. Date also significantly drives patterns in stomach fullness (X2 =60.57, P=0.019), but not in digestion. We used a generalized linear model to account for the corresponding effects of tidal, diel, and seasonal trends as well as difference in habitat affinity for different substrates in driving patterns of catch per unit effort (CPUE). CPUE was significantly different across the course of the fall (F1= 3.00, p=0.093) and in different substrate types (F1= 12.49, p=0.001). This study can be used to inform fisheries managers and add higher resolution to food web models.