Krill Monitoring - Hydroacoustic Data
Euphausiid crustaceans, commonly known as krill, represent a primary food resource for pelagic fish, seabirds and marine mammals in marine food webs. Farallon Institute acoustic data for krill in the California Current are made available (see below) to maximize the impact that data can have to help understand and manage open ecosystems. If you are interested in collaborating with Farallon Institute using the data we have, please contact us.
Acoustic data were analyzed using Echoview software and relative krill abundance is output as Nautical Area Scatter Coefficient (NASC). Over 85,000 NASC samples have been produced from 2000-2018 and NASC value are associated with geo-referenced coordinates. Acoustic data from 2012-2018 have been combined with a newly-derived target strength model to calculate biomass estimates of krill.
Below are key findings and citations to publications produced by Farallon Institute scientists with these data:
Krill biomass estimate: Krill biomass was estimated at 1.75 to 2 million metric tons in Northern and Central California (Cape Mendocino to Point Conception) from 2012-2018. Significant interannual variability was evident, with much lower krill biomass during warm periods and increased krill when coastal upwelling was more intense (Dorman et al. 2021, in review).
Habitat compression: During the 2014-2016 North Pacific Marine Heatwave, forage (krill and anchovy) were compressed closer to shore. This, in turn, drove whale populations closer to shore and increased human (shipping,fishing) and whale interactions, such as entanglements (Santora et al. 2020).
Krill Essential Habitat: Krill hotspots tend to be associated with shelf-incising submarine canyons, in particular with canyons of large area and length. In a highly variable upwelling environment, these features may provide a stable microclimate for krill by facilitating retention of cool, nutrient rich water (Santora et al. 2018).
Krill aggregations and Salmon distribution: The distribution of juvenile Chinook salmon and acoustic estimates of krill aggregations were not closely correlated. However, krill are a critical component of salmon diets and samples were encountered frequently in the stomachs of captured sub-adults and adults which can range over a larger area and can take advantage of more dispersed and patchily distributed prey (Hassrick 2016).
Modeled krill aggregations were compared to hydro-acoustically observed hotspots: Acoustic data were used to validate an individual-based model of krill for the California Current. Acoustic data and modeled krill hotspots showed Monterey Canyon and the greater Gulf of the Farallones as areas of persistent krill hotspots (Dorman 2015).
Krill aggregations and Oceanographic conditions: Krill hotspots were found to be inversely correlated with upwelling centers (due to strong offshore transport) and aggregated downstream of upwelling centers (Santora 2011a).
Krill aggregations and Seabirds: The distribution of krill and seabirds overlapped along the outer shelf and shelf slope regions. This indicates that at-sea distribution of sea birds can be used as indicators of subsurface krill aggregations (Santora 2011b).
Net samples compared to acoustic results targeting krill: Acoustically derived krill estimates were validated with net samples and were more correlated with Euphausia pacifica than Thysanoessa spinifera, the two dominant krill species in the California Current (Santora 2011b).
The maps below show the cruise-tracks where data was collected for each year.
Click on a map image for more information
We thank NOAA Fisheries for contributing raw echosounder data for this project and Bonneville Power Authority for supporting surveys off the Columbian River plume. Support for computer processing and preparation of this data was provided by the Marisla Foundation, National Fish and Wildlife Foundation, NASA, California Sea Grant award and NOAA Fisheries, California Current Integrated Ecosystem Assessment program via the Northwest Fisheries Science Center.