Effectiveness of Airboat Electrofishing for Sampling Fishes in Shallow, Vegetated Habitats

Abstract

We evaluated the effectiveness of airboat electrofishing for sampling large fishes (standard length, SL ≥8 cm) in shallow, vegetated habitats. Concurrent block-netting (0.1 ha) and airboat electrofishing were conducted at 11 sites in freshwater marshes of the Florida Everglades. We found significant positive relationships between log-transformed electrofishing catch per unit effort (CPUE) and both fish density (number/0.1 ha) and biomass (grams dry weight/0.1 ha) estimates from block nets. Analysis of covariance revealed that estimates of species richness were similar for electrofishing and block-net samples after accounting for differences in the total number of individuals sampled. Nevertheless, length-frequency and species-composition data differed between airboat electrofishing and block-net samples. Relative abundance of yellow bullheads Ameiurus natalis, Seminole killifish Fundulus seminolis, sunfishes (Lepomis spp.), and small size-classes of all species, were lower for electrofishing than for block-net samples. Florida gars Lepisosteus platyrhincus, largemouth bass Micropterus salmoides, and large size-classes of all species, had greater relative abundances in the electrofishing samples than in the block-net samples. Despite these differences, CPUE from airboat electrofishing was positively related to fish density in block nets for two size-classes (from 8 to <12 cm SL and ≥12 cm SL). Residuals from the CPUE–fish density regression were unpatterned with respect to water depth, conductivity, and floating-mat volume but were positively related to emergent-stem density. This suggests that electrofishing was less effective in sparsely vegetated habitats, possibly because fish were better able to detect and flee from the airboat. Our study suggests that airboat-electrofishing (log₁₀CPUE) provides a useful index of the abundance of large fishes in shallow, vegetated habitats, but length-frequency and species-composition data should be interpreted with caution. Additionally, emergent-stem density should be included as a covariate in statistical analyses of airboat electrofishing CPUE.