Was over-exploitation the cause of the decline of the American plaice stock off Labrador and northeast Newfoundland?

Abstract

The population of American plaice in the waters off Labrador and on the northeast Newfoundland shelf declined substantially during the mid to late 1980s, early 1990s at a time when reported catches were very low. An earlier study examined the overlap in distribution between American plaice and cod in research vessel survey data and concluded that unreported bycatch in the cod fishery could explain the decline of the Div. 2J portion of the Subarea 2+ Div. 3 K stock of American plaice. We evaluate the method proposed in that study and use reported and observer estimates of catch to investigate potential catch levels relative to survey estimates of population biomass. This method does not appear to be a good predictor of American plaice bycatch in the cod fishery as most of the regressions were not significant and it requires extrapolation well beyond the range of the data used to build the regressions. Furthermore, there was little overlap between the extent of the commercial cod fishing grounds and the distribution of American plaice in the autumn surveys. For this stock, catch to survey biomass ratios were low regardless of the source of information used to estimate catch and suggest an exploitation rate that should be well below sustainable levels. These analyses support the conclusion that fishing was not the cause of the decline in this population of American plaice.