20. Catch-per-unit-of-effort data were only collected from the offshore fleet. This contributed to an overestimate of biomass because of the special conditions of that fishery. The fleet included vessels able to fish around and through pack ice, exposing the cod to a kind of fishing mortality they had not encountered in earlier times. Moreover, northern cod spawn in dense aggregations on the offshore slopes of the Banks. Offshore trawlers targeted cod during these pre-spawning and spawning concentrations which enabled them to maintain high catch rates on a declining stock.