Selectivity and efficiency of two otter trawls used to assess estuarine fish and macroinvertebrate populations in North Carolina

Otter trawl surveys are frequently used to assess estuarine fish and macroi nvertebrate communities. Although these surveys may have similar objectives and sampling areas and seasons may overlap, the sampling gear is usually u nique to the agency conducting the survey. An example of this is the North Carolina Division of Marine Fisheries (NCDMF) and Environmental Monitoring and Assessment Program-Estuaries (EMAP) surveys in North Carolinian estuari es. We estimated experimentally the selectivity and efficiency of the trawl s used for these surveys to determine the comparability of data used to est imate community structure and the abundance of dominant species. The catch percent similarity of the trawls was low (12.0%). The NCDMF net (3.2-m flat otter trawl, 6.4-mm mesh body, 3.2-mm cod-end, plus tickle chain) precisel y (11.7%) and accurately (4.5%) sampled brown shrimp, Penaeus aztecus, dens ity but overestimated spot, Leiostomus xanthurus, densities (22.8% accuracy ), possibly because these fishes had highly contagious distributions. The E MAP net (4.9-m high-rise otter trawl, 38.1-mm mesh body and cod-end) was pr ecise (17.9-37.4%) but inaccurate (76.8-97.2%), probably because of the sin gle large mesh size and the lack of a tickler chain. Our study suggests the EMAP and NCDMF surveys collect different subsamples of the same fish and m acroinvertebrate estuarine populations, and therefore could deliver differe nt results and conclusions.