Climate change threatens net energy uptake, maturation, and reproduction of Pacific Sand Lance (Ammodytes personatus) in the central Salish Sea

Juvenile Pacific Herring and Pacific Sand Lance (PSL) are the main prey of juvenile Chinook salmon migrating seaward through the San Juan Islands. Herring and Sand Lance also dominate the diet of resident Chinook (“Blackmouth”) that undoubtedly played an important historical role in the evolution of resident Killer Whale (Orcinus orca) lineages. Many Salish Sea marine birds target Pacific Herring or Pacific Sand Lance as well. Pacific Sand Lance abundance fluctuates considerably in the central Salish Sea, with an overall downward trend since 2009. The role of this forage fish in the Chinook-Killer Whale food web, and survival of many marine birds, raises questions about the factors driving PSL abundance cycles, and the vulnerability of PSL populations to climate change and marine pollution. Since 2017 we have collected PSL year-round from southeastern Lopez Island, a coast frequented by juvenile Chinook and marine birds, and compared PSL gut contents with prey field data from synchronized zooplankton tows. Adiposity, otolith age, gonad maturity, and genetic data were also collected. Results suggest that PSL in the central Salish Sea are not generalist feeders, but rather “peck” selectively at the largest size classes of calanoid copepods, which other studies have associated with cooler sea surface temperatures. Larvaceans and euphausiids are secondary targets, and when larger crustaceans were scarce, we found that PSL temporarily shift to feeding on the largest diatom species. PSL are relatively long-lived (7-10 years). If individuals commit energy to gonad maturation only in years when prey are abundant, as observed in other Ammodytes species, PSL should be relatively resilient to annual fluctuations in marine conditions and zooplankton prey quality. However, spawning rates will decline in gradually warming seas as larger copepod species decrease, and PSL switch to smaller, harder to handle, less caloric prey