THE EVALUATION AND USE OF GEAR EFFICIENCIES IN THE ESTIMATION OF ESTUARINE FISH ABUNDANCE

Abstract

Accurate estimates of fish abundance are necessary for models of many estuarine processes, but they have generally been unavailable because fish sampling methods are biased. A major source of bias is a fish's avoidance of sampling gear. A brief discussion of theoretical and qualitative information concerning net avoidance and a simple gear efficiency model is presented. Results of quantitative studies on the efficiency of sampling gear have potential for correcting bias due to net avoidance. Discussion of gear efficiency studies for a plankton net, beam trawls, portable drop-net, haul seines and otter trawls are provided and indicate that such research is feasible and can yield useful information. Our ongoing investigation on the efficiency of a 6.1 m otter trawl for Lagodon rhomboides and Leiostomus xanthurus in a North Carolina estuary during 1975 indicates that trawl abundance estimates for these species were only 9 to 51% of the true values. General recommendations are given to assist in limiting the problem of fish sampling bias.