Preliminary investigation of the effects of purse seine size on estimates of density and species richness of estuarine fishes

Small purse seines are well suited to sampling open water habitats in estuaries, yet little is known about how variation in their design affects estimates of density and species richness of estuarine fishes. We tested whether purse seine size (length and depth) affected estimates of density or species richness of fishes in San Dieguito Lagoon, southern California, U.S.A. Twenty-one species were captured, with the open water speciesAtherinops affinis dominating the catch. The larger net (36.4 m long × 3.6 m deep) produced higher estimates of density than the smaller net (18.2 m long × 2.4 m deep). The average number of species captured per sample was lower for the smaller net than the larger net, but species accumulation curves for the small and large nets were similar, indicating that the difference in the number of species per sample was primarily caused by the larger area sampled by the larger purse seine. Sampling with the larger purse seine was more time efficient than the smaller seine. We found small purse seines to be useful tools for sampling fishes in open water habitats in a small estuary, but we recommend that care be taken in selecting the size of a purse seine.