Benthic Habitats and the Effects of Fishing

Symposium Abstract: Impacts of Trawling and Wind Disturbance on Water Column Processes in the Pamlico River Estuary,North Carolina

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

doi: https://doi.org/10.47886/9781888569605.ch116

Comparatively little attention has been given to the indirect impacts of bottom trawling in soft bottom ecosystems. Our study assesses the relative effects of bottom trawling and wind disturbance on water column nutrient (NH4, NO3-NO2, PO4) loading and primary productivity (chlorophyll a concentration, bacterial abundance) in concert with measurements of sediment resuspension and transport (Frank, et al.). We are working in South Creek, a subtributary of the Pamlico River Estuary, NC (USA) that has been closed to trawling for 15 years, and is characterized by large surface area, shallow depth, and wind-driven tides. Trawling experiments in July and October 2001(repeated in 2002) were carried out during two different wind regimes: (a) days of consistent wind direction interrupted by an abrupt 180o shift in direction (July); and (b) continuously shifting wind speed and direction (October). Two replicate areas, each containing a trawled and an untrawled site ~100,000 m2, were sampled for 4 days prior to, and immediately after a trawling event. We were unable to detect a significant difference in any water column parameter (oxygen, nutrients or chlorophyll a) that could be attributed exclusively to trawling. Instead, changes appear to be driven by a variable wind regime. Interestingly, measures of photosynthetic active radiation indicate that 60-80% of incident light is absorbed within the upper 0.5m of the water column. These findings imply that South Creek and physically similar regions of the Pamlico River Estuary are light-limited systems in which windforced mixing events are primarily responsible for sediment resuspension from the benthos.