Was the Increase in Shrimp Biomass on the Northeast Newfoundland Shelf a Consequence of a Release in Predation Pressure from Cod?

Biological changes in the ecosystem of the Northeast Newfoundland Shelf during the late-1980s and 1990s included a collapse in the biomass of cod (Gadus morhua), a substantial increase in the biomass of northern shrimp (Pandalus borealis), and an expansion in the area fished for shrimp. The timing and magnitude of changes in cod biomass and the quantity of shrimp consumed by cod were explored to determine if they were consistent with the hypothesis that the increase in shrimp biomass was a consequence of a reduction in predation pressure from cod. Results are equivocal because the timing of both the increase in the shrimp stock and the decline in the cod stock remain unclear and there is considerable uncertainty in the estimates of consumption of shrimp by cod. Nevertheless, it appears that an initial increase in shrimp biomass must have occurred during the early to mid-1980s and was not related to changes in the cod, whereas a larger increase in shrimp biomass in the 1990s was related at least in part to the collapse of the cod.