Spatiotemporal variation in Pacific sand lance (Ammodytes hexpaterus) abundance and demographics in the San Juan Channel

Abstract

Fish feeding behavior, abundance, and population demographics depend on a number of environmental and non-environmental factors. Some fish, such as salmonids, display cyclic population structures and year class strength that are independent of their environment (Selbie 2008), whereas other fish are strongly influenced by light (Friedlaender et al. 2009), temperature (Cowx and Frear 2004) and tides (Witt 2011). Pacific sand lance (Ammodytes hexapterus) exhibited potential cyclic structures in previous studies, making them ideal for this abundance and population demographic study. Sand lance were collected from the San Juan archipelago and were examined to determine within-day, seasonal, and inter-annual patterns between: foraging behavior and light, time, and tides; abundance (catch per unit effort, CPUE), condition (condition factor, K), and age group structures. Together, these data suggest that sand lance foraging behavior is influenced tidal heights, although greater resolution is needed to determine the effects of other environmental conditions. Across larger temporal scales, local sand lance populations were in much lower condition that in previous years, suggesting the fall of 2014 had unusual environmental conditions. Finally, the sand lance exhibited a cyclic population structure with regards to year class strength, although not in abundance patterns. Further studies in sand lance abundance and population demographics would be useful to confirm this pattern.