Spatiotemporal variability of euphausiids in the California Current Ecosystem: insights from a recently developed time series

Abstract

Abstract Euphausiids, or krill, are important energy links between primary producers and higher trophic levels in the California Current Ecosystem (CCE), but a thorough understanding of their variability at the coast-wide scale is limited. Using fisheries acoustics data collected during biennial joint US–Canada Integrated Ecosystem and Acoustic Trawl Surveys for Pacific hake (Merluccius productus), we developed a time series (n = 8 years; 2007–2019 odd years inclusive, and 2012) of krill abundance and examined relationships with environmental factors. Krill were located in waters off the west coasts of the United States and Canada, primarily in shallow basins and on the continental shelf, with greatest kernel density estimates near Cape Mendocino and the Juan de Fuca eddy system. Coast-wide krill abundance was variable, and lowest in 2015 during an extended marine heat wave, when 91% were located in British Columbia. Using hierarchical generalized additive models, we predicted greatest krill abundance in cooler waters (0.2°C below the time series average), within 10–20 km of the shelf break, and in bottom depths between 200 and 400 m. This newly developed coast-wide time series of krill abundance and distribution will inform ecosystem-based fisheries management efforts, and offers additional opportunities for studies of krill-dependent fish, seabirds, and marine mammals.