Water mass and bathymetric characteristics of polar cod habitat along the continental shelf and slope of the Beaufort and Chukchi seas

Relatively little is known about the distribution of fish in deep water (> 200 m) in the Beaufort Sea. Data collected by an Acoustic Doppler Current Profiler operated in the Chukchi and Beaufort seas in summer were examined for evidence of fish biomass detections between 18 and 400 m. The presence of fish in waters between 1 and 30 m was explored opportunistically with a non-scientific echo sounder. Evaluation of findings was enhanced by measurements of water column properties (temperature, salinity, fluorescence and transmissivity). Relatively small shoals of fish were detected on the Chukchi shelf and eastern Chukchi shelf break, and also on the Alaskan and Canadian Beaufort shelves in the upper 20 m (T = 2-5A degrees C). Much larger shoals (putative polar cod) were detected within Atlantic Water along the Beaufort continental slope (250-350 m) and near the bottom of Barrow and Mackenzie canyons, where temperatures were above 0A degrees C. A warm-water plume of Alaska Coastal Current water with high concentrations of phytoplankton, zooplankton, and fish was found extending along the shelf 300 km eastward of Barrow Canyon. In contrast to the warm surface and Atlantic Water layers, very few fish were found in colder, intermediate depth Pacific-origin water between them. The large biomass of fish in the Atlantic Water along the continental slope of the Chukchi and Beaufort seas represents previously undescribed polar cod habitat. It has important implications with regard to considerations of resource development in this area as well as understanding impacts of climate change.