Vertical distribution and foraging of marine fish arvae under the ice cover of southeastern Hudson Bay

Abstract

In ice-covered southeastern Hudson Bay (northern Quebec, Canada) the production of suitable zooplankton prey for manne fish larvae was simdar withln and outside the area covered by the Great Whale hver plume Within the plume however, hght attenuahon by the turbld surface layer reduced the foraging efficiency of first-feeding Arctic cod Boreogadus sa~dan d sand lance Ammodytes sp larvae In daytime, first-feeding larvae accumulated at the pycnocline where food availability (l e light X prey density) was maximum Below the pycnocline, the average number of prey lngested by indiv~duala rvae (foraging gain) decllned with depth At night, fish larvae and their prey redistnbuted more uniformly over the water column, suggesting a similar passive response to the turbulence field In the absence of a light gradient The observed Ideal free distributions (IFDs) were better explained by unequal foraging abilities of the larvae than by density-dependent interactions among the assemblage of planktonic predators