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Monitoring freshwater fish in Florida lakes using electrofishing: Lessons learned

Hoyer, Mark V., Bennett, Jason P., Canfield, Daniel E.
Lake and reservoir management 2011 v.27 no.4 pp. 329-342
altitude, animal communities, aquatic plants, chlorophyll, freshwater fish, game fish, lakes, monitoring, multivariate analysis, species diversity, surface area, variance, Florida
Electrofishing was used in 30 Florida lakes to monitor fish communities over an 8-year period. Six 10-minute electrofishing transects were used annually per lake to estimate the catch per unit effort (CPUE, gm/hr) total fish, sport fish, and each individual fish species. A variance components analysis using CPUE as the dependent variable and lake, year within lake, and transect within year and lake as independent variables showed that in almost every case transect accounted for more than 50% of the variance in CPUE. The estimated variance from this sampling effort showed that the average number of electrofishing transects needed to estimate total fish and sport fish CPUE within 20% of the mean at a confidence of 95% would have to double and triple current effort, respectively. Lake trophic status, estimated with chlorophyll concentrations, was also monitored and showed a direct positive relation with total fish and sport fish, even with low sampling effort, providing a general ability to estimate CPUE in Florida lakes. After accounting for lake trophic status, estimates of aquatic plant abundance did not account for more variance in CPUE estimates because the sampling effort was not rigorous enough for multivariate analyses. Eight years of repeated sampling yielded an asymptote for cumulative species richness. Lake surface area and altitude were directly and inversely related to species richness, respectively, together accounting for 43% of the variance in species richness. Lake managers interested in monitoring fish populations should conduct a pilot study to estimate sampling frequency needed to answer stated objectives.