OceanCanada Contributor: Smith R

Sea-cage finfish aquaculture frequently spatially overlaps and competes with traditional fisheries and ecologically important habitats in the coastal zone. Yet only few empirical studies exist on the effects of sea-cage aquaculture on commercially important fish and shellfish species, due to the lack of data. We present results from a unique collaboration between scientists and lobster fishers in Port Mouton Bay, Atlantic Canada, providing 11 yr of market (market-sized) lobster catches and berried (ovigerous) lobster counts in 5 spatially resolved areas adjacent to a sea-cage finfish farm. The time series covered 2 stocked (feed) and 2 non-stocked (fallow) periods, allowing us to test for the effects of feed versus fallow periods. Our results indicate that average market lobster catch per unit effort (CPUE) was significantly reduced by 42% and berried lobster counts by 56% in feed compared to fallow periods. Moreover, both market and berried lobster CPUE tended to be lower in fishing region 2, which included the fish farm, and higher in region 5, furthest away from the farm. Bottom temperature measurements in one region suggest that differences in CPUE between feed and fallow periods were not driven by temperature, and that berried lobsters may be more sensitive to both aquaculture and temperature than market lobster. We discuss possible mechanisms of how finfish farms as well as other abiotic and biotic factors such as habitat quality and temperature could affect lobster catch. Our results provide critical information for the management of multiple human uses in the coastal zone and the conservation of shellfish habitats that sustain traditional fisheries.