It takes guts to locate elusive crustacean prey

Abstract

Mobile crustacean prey, i.e. crangonid, euphausiid, mysid, and pandalid shrimp, are vital links in marine food webs. Their intermediate sizes and characteristic caridoid escape responses lead to chronic underestimation when sampling at large spa- tial scales with either plankton nets or large trawl nets. Here, as discrete sampling units, we utilized in- dividual fish diets (i.e. fish biosamplers) collected by the US National Marine Fisheries Service and North- east Fisheries Science Center to examine abundance and location of these prey families over large spatial and temporal scales in the northeastern US shelf large ecosystem. We found these prey families to be impor- tant to a wide variety of both juvenile and adult dem- ersal fishes from Cape Hatteras to the Scotian Shelf. Fish biosamplers further revealed significant spatial shifts in prey in early spring. Distributions of mysids and crangonids in fish diets shoaled significantly from February to March. Distributions of euphausiids and pandalids in fish diets shifted northward during March. Of multiple hypotheses for these shifts, prey migration is most strongly supported. Rather than only the classic ontogenetic shift from feeding on shrimp to piscivory, of the 25 identified diet shifts in fish predators, 12 shifts were toward increased shrimp feeding frequency with increasing body length.