Comparisons of Wegener Ring and O.OS-Hectare Block Net Samples of Fishes in Vegetated Habitats

Density, biomass, and species composition of fish 6 em total length (TL) were determined in 4 aquatic plant communities in Lake Okeechobee, Florida, with 0.08-ha block nets and Wegener Rings (0.004 ha). Wegener Rings were placed within block nets prior to rotenone application. In Illinois pondweed (Potamogeton illinoensis), mean density and biomass estimates derived with the 2 gears were not significantly different. In eel-grass (Vallisineria americana) and hydrilla (Hydrilla verticillata) , mean density estimates derived with Wegener Rings were significantly higher than those derived with block nets, but mean biomass estimates were similar. In yellow water-lily (Nymphaea mexicana) , Wegener Rings provided significantly higher estimates of both mean density and biomass. Gear comparisons within sample sites revealed that at the highest fish densities encountered in each vegetation type, Wegener Rings provided significantly higher density estimates than block nets. If it is assumed that more complete retrieval of small fish from the Wegener Rings provide more accurate estimates of density, then block net samples in Illinois pondweed, eelgrass and hydrilla underestimated total fish density from 17% to 397% and total biomass from 0% to 26%. In yellow water-lily, block nets underestimated total fish density from 451% to 936% and underestimated biomass from 30% to 56%. Wegener Rings collected 62% to 91% of the species collected by block nets. Species not collected in Wegener Rings were present in low densities in block nets. Data suggest Wegener Rings can be used to estimate density and biomass of small fish within block nets in shallow « 1.5 mdepth), densely vegetated habitats. Wegener Rings provided similar or more accurate estimates than block nets and reduced total effort necessary to collect and process samples.

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