Trophic Ecology of the Pacific sand lance, Ammodytes hexapterus, in the San Juan Channel

Abstract

Forage fish, such as the Pacific sand lance (Ammodytes hexapterus) occupy a critical intermediate trophic level characteristic of wasp waist food webs. Though Pacific sand lance (PSL) are prey to numerous organisms, little research has been conducted on the trophic ecology of PSL in the San Juan Channel (Salish Sea, Washington, USA). This study examined PSL prey fields in the San Juan Channel (SJC), as well as short term dietary patterns of the PSL during the autumn of 2013. Additionally, this study aims to characterize both long term nutrient assimilation and trophic position of PSL in the SJC using stable isotope analysis (SI). Zooplankton sampling revealed that PSL prey field composition was similar for all sites sampled. Results indicated that zooplankton composition and abundance in the SJC is influenced by environmental drivers including wind and tidal cycle. Gut content analysis revealed that PSL fed preferentially upon calanoid copepods. Secondary prey items included harpacticoid and cyclopoid copepods (20%), and amphipods (13%). There were no significant diel dietary patterns, but there were interannual differences, including the lack of larvaceans and copepod nauplii in 2013 gut contents. The results of SI have not been received at this time.