Distribution and Variation between Populations of Pacific Sand Lance in the San Juan Archipelago

Abstract

In the San Juan Islands, the immediate trophic levels of the marine food web represent a critical link that is largely constituted by forage fish, including the Pacific Sand Lance. This document contains the results of an in-depth study of the morphological and conditional differences between Pacific Sand Lance populations at different depths. Beach seines were used to retrieve fish from shallow water (Jackson Beach), and Van Veen grabs were used to sample from deep water (the San Juan channel wave field). The fish observed at the wave field were larger and heavier than those at Jackson Beach, both across the season and on a discrete, week- by-week scale. There was a slight disparity in hibernation periods between depth populations. In the wave field, most of the fish at that site began hibernating during the second half of October as interpreted from the stomach fullness of fish. In contrast, the majority of the fish at Jackson Beach began hibernating two weeks earlier, during the first half of October. Finally, the dietary analyses of both sites suggested multiple hypotheses of life histories, including that the Pacific Sand Lance are selective feeders, and that their preferences vary with age.