Identifying the effects of fishing on marine communities

Simon Thrush

This talk emphases the role of scientific information in the wise management of marine ecosystems. A case study is presented that identifies the broad-scale changes in seafloor communities due to habitat disturbance by dredging and trawling. The study design recognised the lack of adequate control sites against which to assess effects and the important role of ecological heterogeneity in functioning of ecological systems. Instead, a series of predictions based on general ecological disturbance theory and experimental studies of trawl and dredge disturbance were tested. Predictions were validated for a variety of groups of seafloor dwelling animals. Of these, the most important may be the increase in the density large animals living on the sediment surface and an increase in biodiversity with decreasing fishing pressure. We were able to attribute 15 - 20 % of the variability in the composition of the seafloor animal community to fishing. This study provides strong evidence that fishing does cause broad-scale changes to seafloor communities. Particularly by decreasing diversity and functionally important habitat complexity. These findings are discussed in light of the need to asses the effect of fishing on marine ecosystems and develop management strategies to ensure the development of ecologically sustainable fisheries.

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