Impact on biodiversity of scallop dredging in San Matías Gulf, northern Patagonia (Argentina)

Abstract

Between 1968 and 1994, Tehuelche scallop (Aequipecten tehuelchus) was fished in San Matias Gulf (Argentine Patagonia) using dredges. The catch was not sorted on board; epifaunal invertebrate bycatch and inorganic substrate removed by the dredges were landed together with scallops. Surveys were conducted in 1987 and 1997 on four fishing grounds following the same methodology to estimate the abundance of epifaunal components using catch and swept-area data. Univariate, distributional, and multivariate methods were used to analyze biodiversity and its change between surveys. There was no recorded dredging on two of the fishing grounds in the intervening period between the two surveys. Fishing effort in the order of 5,000 effective fishing hours occurred at each of the other two grounds, during that period. Multivariate analysis indicates that macrofaunal assemblages changed in each ground between 1987 and 1997, according to fishing intensity and time lapsed since last fishing action. Fishing grounds that were not dredged during the 10-year period showed no significant changes in species composition and dominance. The results support the hypothesis that dredging causes high levels of disturbance that affect the whole benthic ecosystem. Community “recovery” seems to be a non-stationary process that may not reverse the system to pre-harvest conditions, but lead instead to a sequence of new states with faunistic changes governed by colonization and slow rebuilding of habitat complexity.