ACCURACY OF FISH POPULATION ESTIMATES IN A NAVIGATION CANAL WITH HEAVY TRAFFIC

A high sampling efficiency and precision of fish population density es timates with three seine nets laid together and hauled individually to wards a stop net were achieved in the Shropshire Union Canal (England) despite very heavy boat traffic (9500-10000 number of movements per h ectare per year). For roach, and also for perch and ruffe, for 14.3% o f estimates, the number of fish collected equalled estimated density ( (N) over cap); and also for 52.4% of estimates, 95% CL constituted les s than 10% of (N) over cap, which assures precision of production esti mation, especially of yield. The method may have an application in man y water bodies where the bed is level and without obstacles for haulin g net, and water current is less than 2 km h(-1). (C) 1998 Elsevier Sc ience B.V. All rights reserved.