Benthic Habitats and the Effects of Fishing

Symposium Abstract: Effects of Fishing on Organic Carbon Content of Sand Habitats on Georges Bank

V. G. Guida, A. Paulson, P. C. Valentine, and L. Arlen


A 4.5 year closure to fishing of an area on Georges Bank provided an opportunity to compare physical and chemical characteristics of sand habitats from areas that had not been subjected to fishing with adjacent areas that had been fished. Sediment cores (6-15 cm deep) taken by Van Veen grab sampler in June 1999 were sectioned into 1 cm depth segments and analyzed for Total Organic Carbon (TOC, particulate plus interstitial), and for grain size. Grain size was the most important factor influencing TOC, which correlated positively with mud content. Where similar grain size distributions occurred at nearby stations inside the area closed to fishing and outside, TOC values were significantly higher in the upper sediment layers of inside (unfished) stations. Comparing TOC between inside-outside station pairs with similar grain sizes revealed two distinct patterns, suggesting two distinct mechanisms for TOC depletion. In the first, TOC of the upper 2 cm of the fished station was depleted compared to the unfished station. This probably reflects advection of depositional organic matter upon resuspension by fishing. In the second pattern, the sediment column from the fished station was depleted in TOC relative to unfished sediments to a depth of 5 cm or more. This pattern may reflect an overall increase in remineralization resulting from vertical redistribution of labile organic substrates and oxidants from the surface by fishing turbation. Which mechanism predominates may depend upon bottom hydrology, the rate and composition of organic matter deposition, and the texture and dynamics of the sediments.