Changes in finfish community structure associated with an offshore fishery closed area on the Scotian Shelf

In 1987 a large area (~13 700 km 2 ) associated with 2 offshore banks on the Scotian Shelf (Nova Scotia, Canada) was closed to commercial trawling for groundfish in order to protect the juvenile stages of haddock Melanogrammus aeglefinus from discarding. We assessed possible changes in the finfish community structure before and after the closure. Species abundance data collected annually since 1970 were subjected to multivariate analyses such as cluster analysis and a randomization/permutation test. Finfish community composition was significantly different after the implementation of the closure, and several species contributed to the post-closure difference including herring Clupea harengus, winter flounder Pseudopleuronectes americanus and redfish Sebastes sp., which showed dramatic increases in abundance. Haddock was the dominant species throughout the entire period. These findings suggest that several members of the finfish community benefited from the area closure. However, community structure in a reference area that has never been closed to fishing (Browns Bank) became more similar to the community structure in the closed area, contrary to our expectations. We provide support for the hypothesis that the dynamics of the Browns Bank area finfish community are coupled to the closed area through spillover based on several lines of inquiry, including positive relationships between abundance and area occupied of the dominant species and non-contemporaneous increases in species abundance between the closed area and the Browns Bank area with lags ranging from 1 to 3 yr. This study argues that establishment of fishery closures is likely to have positive benefits to the component species at both local and regional scales; however, the time-scale for such changes appears to be relatively long in comparison to tropical systems.