Evaluation of Arctic Cod and Age-0 Fish Density Distributions in the Beaufort Sea

A survey in the U.S. portion of the Beaufort Sea during August 2008 used acoustics, nets (midwater, bottom, zooplankton), and oceanographic observations to inventory and characterize distributions of fish and invertebrates (demersal results presented in a companion presentation by L. Logerwell). Within this study, acoustics (38 kHz) and midwater trawling were used to assess density distributions of age-1+ Arctic cod and age-0 fish (Arctic cod, sculpin, eelblenny). Age-0 fish dominated areas with bottom depths <75 m and were observed in near surface waters (<50-75 m) throughout the survey area. Density distributions of age-0 fish suggested that near-surface densities in the 100-500 m depth stratum increased from west to east. In all regions, age-0 fish were associated with warmer, less saline water possibly of ice melt or river origin. Age-1+ Arctic cod densities were highest in areas with bottom depths >100 m, with peak densities occurring in areas with approximately 200 m bottom depth. Age-1+ density distributions were consistent with the distribution of cold, saline water within the study area, and may suggest that age-1+ Arctic cod are associated with oceanographic conditions such as Chukchi Sea water inflow rather than bathymetry. Large age-1+ Arctic cod aggregations were detected in the 41-100 m depth stratum overlapping with dense regions of age-0 fish. Age-1+ concentrations in the vicinity of the shelf break (100-300 m) were striking as they coincide with published foraging locations of beluga whales (Delphinapterus leucas) along the continental slope. This study was the first to evaluate the relationship between summertime age-1+ Arctic cod and age-0 fish distribution patterns and oceanography.