Feeding Ecology of Pacific Sand Lance in the San Juan Archipelago

Abstract

Forage fishes such as Pacific Sand Lance Ammodytes personatus are a crucial link between lower and upper elements in marine food webs, as they transfer energy from plankton to higher trophic levels. Despite their importance to marine food webs, little is known about the population structure and feeding ecology of Pacific Sand Lance. In this study, we examined the population density and diet composition of Pacific Sand Lance as well as feeding patterns and movement in response to tidal, diel, and seasonal cycles in a prominent sand wave field in the San Juan Channel, Washington. A generalized linear model was applied to account for the corresponding effects of tidal, diel, and seasonal trends as well as habitat affinity related to substrate type. We showed that fish distributions were predominantly driven by sediment type and that time of day had a significant influence on foraging behavior with distinct crepuscular feeding patterns. Our results also provide evidence for the cessation of feeding over the fall transition and the onset of a winter dormant period, as observed by increased densities of fish within the sand wave field (177%), a marked increase in the number of empty stomachs (511%), and a significant decrease in condition factor. These trends correspond with the expectations that Pacific Sand Lances exhibit a winter dormant phase and burrow in sediments throughout the winter months to conserve energy and reduce predation risk during periods of low productivity. We anticipate our study to be a starting point for understanding the foraging ecology of the Pacific Sand Lance, particularly in the San Juan Archipelago and Salish Sea. The results of this study may improve the understanding of Pacific Sand Lance habitat and availability to pelagic predators, inform fisheries management, and increase the resolution of marine food web models.

Received March 15, 2017; accepted August 9, 2017

ACKNOWLEDGMENTS

We thank J. Newton, B. Tyler, and R. McLaughlin for their assistance and continued support. We also thank and acknowledge G. Greene and J. Aschoff for the use of multibeam graphic images of the sand wave in the San Juan Channel and assistance with geospatial analysis, T. Sigley for analysis of zooplankton samples, B. Matta for insight on age–length estimates and otolith analysis, A. Summers and J. Bizzarro for their professional expertise and insight on sediment association, and T. Wyllie-Echevvera and M. Rood for their insights and historical perspective. We also thank K. Rose as well as three anonymous reviewers for their recommendations and advice to improve our manuscript. We are particularly appreciative of the considerable contributions of D. Willows and W. Krieger of the RV Centennial and colleagues in the 2012 Pelagic Ecosystem Function apprenticeship, particularly C. Heller and A. Thomson, as well as the those from the community of the Friday Harbor Lab for their assistance throughout the course of this study and analysis.