Bacterial Community Profiling of the Eastern Oyster (\u3cem\u3eCrassostrea virginica\u3c/em\u3e): Comparison of Culture-Dependent and Culture-Independent Outcomes

Tissue-associated bacterial community profiles generated using a nested polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) approach and culture-dependent and culture-independent isolation techniques were compared. Oyster samples were collected from 2 harvest areas along the coast of Maine, in the United States. Profiles from both isolation strategies were evaluated using Sorensen’s index of similarity and cluster analysis of gel banding patterns. Culture independent profiles were further evaluated using the Shannon diversity index. In general, the culture-dependent strategy resulted in a greater number of bands within a profile. Bacterial DGGE profiles were found to be highly similar within an isolation strategy, with a higher degree of unrelatedness between culture-dependent and -independent techniques. Cluster analysis identified bands present in the culture-dependent strategy and not the total DNA technique, and vice versa. Significant differences in community profiles between oyster-associated and seawater were observed, indicating a diverse group of specialist bacterial species inhabit and are able to proliferate within the oyster

Shrimp Separator Trawl Experiments: Gulf of Maine Shrimp Fishery

The discard of finfish bycatch in the Gulf of Maine, northern shrimp trawl fishery is considered a serious problem. The species specific discard rate varied from 17% for winter flounder to 95% for silver hake in fifty tows made by commercial trawlers during the period 1985-1989 (Howell and Langan, 1990). Studies by Jean (1963) and Howell and Langan (1987) suggest a very high mortality for discarded finfish in the Western North Atlantic fisheries. The discard problem has two major facets: direct wastage in throwing back fish into the sea and loss of future catches of larger animals through the mortality of small individuals (Saila 1983). Given the perceived problem of discarded bycatch in the Gulf of Maine shrimp fishery, the objective of this project was to experiment with several design modifications to existing traditional trawls that would reduce the juvenile finfish bycatch. The concept of selective shrimp trawls is not novel. Trawl design modifications have been evaluated in shrimp fisheries to separate the finfish from the shrimp with varying success. The techniques utilize behavioral and size differences between shrimp and finfish, and include horizontal separator twine panels, large mesh escape panels, deflecting grids, accelerator funnels, and others. In this project, the northern style shrimp trawls served as the control nets. The basic modifications evaluated were: large mesh in belly area and a funnel accelerator ahead of the trawl cod-end

Fishing activities

Unlike the major anthropogenic changes that terrestrial and coastal habitats underwent during the last centuries such as deforestation, river engineering, agricultural practices or urbanism, those occurring underwater are veiled from our eyes and have continued nearly unnoticed. Only recent advances in remote sensing and deep marine sampling technologies have revealed the extent and magnitude of the anthropogenic impacts to the seafloor. In particular, bottom trawling, a fishing technique consisting of dragging a net and fishing gear over the seafloor to capture bottom-dwelling living resources has gained attention among the scientific community, policy makers and the general public due to its destructive effects on the seabed. Trawling gear produces acute impacts on biota and the physical substratum of the seafloor by disrupting the sediment column structure, overturning boulders, resuspending sediments and imprinting deep scars on muddy bottoms. Also, the repetitive passage of trawling gear over the same areas creates long-lasting, cumulative impacts that modify the cohesiveness and texture of sediments. It can be asserted nowadays that due to its recurrence, mobility and wide geographical extent, industrial trawling has become a major force driving seafloor change and affecting not only its physical integrity on short spatial scales but also imprinting measurable modifications to the geomorphology of entire continental margins.Fil: Oberle, F.K.J.. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Puig, P.. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Martín de Nascimento, Jacobo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin