Comparisons of Haul Seine and Otter Trawl Catches of Black Crappie and the Evaluation of Haul Seines for Future Research

摘要

We compared the size structure, estimated mean total length (TL) at age, and estimated mortality of black crappie Pomoxis nigromaculatus caught by otter trawl and haul seine at two Florida water bodies (Lakes Parker and Griffin) and used the capture data, estimates of gear-induced mortality, and fishing variables (i.e., fishing effort and volume sampled) to evaluate the efficacy of using haul seines in future projects. Haul seines captured a smaller size range of black crappie than did trawls, and black crappie did not appear to be recruited to the haul seines until they attained 209 mm TL. Haul seines tended to capture proportionally more large fish than did trawls, when considering individuals 210 mm or longer. Mean TL-at-age estimates tended to be larger for haul seines due to differences in gear selectivity. At Lake Parker, trawl captures produced a greater annual mortality estimate (A), and the differences between catch curve slopes were significant. At Lake Griffin, however, haul seines produced a larger value of A, but the differences between the two catch curve slopes were not significant. Gear-induced mortality estimates of sport fish (bluegill Lepomis macrochirus, redear sunfish L. microlophus, and black crappie) captured with the haul seines ranged from 3.2% to 24.2% but varied with species, with black crappie mortality rates being the highest. Haul seines required a relatively high level of effort but provided a larger sample size of black crappie 210 mm or longer than did trawls because of extreme differences in the volume of water sampled and trawls' selectivity for smaller fish. A smaller-mesh haul seine would allow us to sample larger size ranges of fish and increase the number of age-classes captured by the gear, which may allow for more accurate estimates of the population size and age structures. However, the size selectivity patterns of black crappie captured by the haul seine are not known, and further research is recommended to evaluate haul seines with smaller mesh sizes.