Acoustic Estimates of Krill Distribution and Abundance in the California Current Ecosystem

Forage species conservation and management is essential for preserving the health of marine ecosystems. In the California Current Ecosystem (CCE), multiple species of euphausiids, predominantly Euphausia pacifica and Thysanoessa spinifera, comprise a large proportion of the epipelagic and neritic macrozooplankton community. Due to their abundance and widespread distribution, these “krill” have a pivotal role in the sustainability of many marine mammals, seabirds, and fish species, and have therefore been granted Federal protection in 2009. The Federal ban on krill harvest builds upon earlier state-level protection, effectively banning krill fisheries in the western-continental US exclusive economic zone. Despite these protections, krill abundance might oscillate greatly in response to oceanic forcing, affecting the populations of their predators. Thus, to ensure appropriate managing of the CCE, it is essential to periodically monitor, model, and forecast krill biomass. During summer 2012, 2013, and 2014, acoustic-trawl surveys were conducted to survey epipelagic fish species of commercial importance. We augmented these surveys with plankton net samples krill species and lengths, to estimate target strengths and apportion krill backscatter. Here we provide the first estimates and time-series of krill abundance and distribution in the CCE, spanning from the Mexico-US border to the US-Canada border.