An investigation of the cumulative impacts of shrimp trawling on mud-bottom fishing grounds in the Gulf of Maine: effects on habitat and macrofaunal community structure

摘要

The cumulative impacts (i.e. collective, multi-year effects) of seasonal commercial shrimp trawling on habitat and macrofaunal community structure were investigated for two mud-bottom fishing grounds and adjacent untrawled areas in the Gulf of Maine. Habitat structure on mud-bottom fishing grounds did not differ significantly from that in similar untrawled areas. Moreover, sediment resuspension associated with shrimp trawling did not appear to result in net loss of deposited material on fishing grounds, but there is evidence that trawling may alter sediment mixing regimes. Visual inspection of the sediment surface in trawled areas revealed minimal evidence of fishing gear disturbance (such as door, bobbin, or net marks), but biological disturbance features, including numerous large burrows, pits, and dense aggregations of the brittle star Ophiura sarsi, were present in both trawled and untrawled areas. Macrofaunal communities on the two fishing grounds exhibited different responses to shrimp trawling, which were attributed to disparities in levels of fishing activity during the 2000—2001 shrimp season. The results suggest that seasonal shrimp trawling produced at least short-term changes ( < 3 months) in macrofaunal community structure, but did not appear to result in long-term cumulative changes. Resilience to trawling disturbance may be due in part to high levels of biological disturbance generated by benthic megafauna, such as lobsters and fish. By burrowing, pit-digging, and possibly foraging, these animals rework sediments to a depth of 16-17 cm, creating a natural level of disturbance that appears to maintain macrofaunal communities in a perpetually low succes-sional state, so potentially minimizing trawling impacts.