Spatial and temporal variation of late summer ichthyoplankton assemblage structure in the eastern Chukchi Sea: 2010–2015

Abstract

The survival of the planktonic stages of marine fishes is widely considered to be a bottleneck in recruitment success and is a period when fishes are highly sensitive to changes in their environment. In high latitude areas that are forecasted to experience warming temperatures, it is critical to determine a baseline of ichthyoplankton assemblages to detect how the ecosystem may change in response to shifting conditions. This study used ichthyoplankton data from the eastern Chukchi Sea in the summers of 2010–2015 to assess temporal and spatial variation in assemblage structure. Larval densities were examined in relation to oceanographic conditions at depth and corresponding water masses. Additionally, the standard lengths of polar cod (Boreogadus saida), a key trophic link in Arctic food webs, were assessed for size-at-catch relationships. In 2010 and 2011, years of widespread presence of warm, low salinity bottom water masses such as Alaska Coastal Water, yellowfin sole (Limanda aspera) and longhead dab (Limanda proboscidea) dominated the assemblages. In 2012 and 2013, the increased presence of colder, more saline Winter Water coincided with a shift to polar cod-dominated assemblages. In 2014 and 2015, water masses were less spatially defined and different assemblages, characterized by Arctic sand lance (Ammodytes hexapterus) and saffron cod (Eleginus gracilis), were detected than previous years. The greatest range in sizes of polar cod was observed in 2014, as well as the highest number of juveniles and age-1 individuals were collected. The biophysical patterns identified here support the strong connection between interannual oceanographic conditions and ichthyoplankton assemblages which reflect the importance of continuous, multi-year surveys to document assemblage changes in the Arctic.