Benthic Habitats and the Effects of Fishing

Symposium Abstract: Comparative Evaluation of Natural and Trawling Sediment Disturbance via Short-Lived Radionuclides, in situ Monitors and Remote Sensing Techniques in the Pamlico River Estuary,North Carolina

J. E. Frank, D. R. Corbett, T. West, L. Clough, and W. Calfee


Seabed disturbance by bottom trawling has emerged as a major concern related to the conservation of essential fish habitat and water quality. Bottom sediments directly affect water quality by releasing nutrients when freshly deposited organic matter is remineralized. Resuspension and subsequent transport of bottom sediments disturbed by natural physical mixing (e.g. wind) of overlying waters or anthropogenic interactions (i.e. trawling) results in the advective release of dissolved constituents (NH4, NO3-NO2, PO4) from interstitial waters into overlying surface waters. Our study attempts to delineate natural resuspension and transport of surface sediments from trawling disturbances in South Creek, a shallow tributary of the Pamilco River, North Carolina. Our study site encompasses two similar areas, both containing a trawled and untrawled region (~100,000 m2 per region). Within each region, concentrations of total suspended solids, dissolved nutrients and surface sediment inventories of 234Th and 7Be were quantified several days before and after a controlled trawling event. In addition, meteorological information (wind speed, direction, etc.) was collected in close proximity to the study site. Our first set of experiments, July and October 2001, suggest that trawling plays a minor role in sediment resuspension relative to natural wind events. Work to be conducted during summer 2002 will incorporate satellite imagery (AVHRR SeaWiFS) and in situ monitoring devices (current velocity, CTD, turbidity) to further constrain the importance of natural vs. trawling induced resuspension. We hope our techniques will provide the basis for operational monitoring, and provide ‘real-time’ information to resource managers.