Total Krill Abundance, 2002-2018

Krill (euphausiids) are important prey for many mid and upper-trophic level marine organisms due to their global distribution, high biomass, and high energy content. Understanding drivers of krill habitat is essential for forecasting species range shifts, and to better understand how krill predators respond to climate change. Cimino et al. hypothesized that the distribution and abundance of krill species derived from ecosystem surveys in spring and summer relate to geomorphic features, coastal upwelling during the preceding winter, and spring mesoscale oceanographic conditions.

For each year from 2002 to 2018, Cimino et al. predicted their “Full model” onto environmental data in May from the core sampling region and the U.S. West Coast to compare the distribution and abundance of krill species. The “Full model” was tuned to the Spring season (May-June) and included a combination of important variables that were selected following three separate models that were hypothesized drivers of krill distribution: 1) geomorphology (Geomorphic model), 2) preceding winter upwelling dynamics (Winter model), and 3) ocean conditions during the survey (May model). The authors found that the total krill model, in general, showed a high abundance of krill from the nearshore to over the continental slope.

These maps summarize the annual “total krill” full model outputs to the temporal mean, maximum, and minimum total krill abundance across 2002-2018. The annual 2002-2018 data rasters were processed in Python using the xarray package to summarize the data.

In these maps, krill abundance is measured in ln(CPUE+1), which is “the abundance of all krill species in log-transformed catch-per-unit-effort”.