Capture efficiency of a fine mesh seine in a large river: Implications for abundance, richness, and diversity analyses

Seining is a commonly used method for sampling fishes in shallow water, but studies that rely on data collected by seining rarely include corrections based on varied capture efficiencies for species or size classes, or account for false negative errors of detection. We sampled fishes in shallow, nearshore areas of a large river using a fine-mesh seine within a blocknet to estimate capture efficiencies for age-0 and yearling-and-older (YAO) fishes, make comparisons among species (within age groups), and determine if capture efficiencies were affected by water depth and aquatic vegetation cover. We also estimated the proportions of sites that individuals were present but not detected for each species, compared estimated taxa richness and Shannon diversity index values to true values, and determined if richness estimates were affected by water depth and aquatic vegetation cover. We found that capture efficiencies of age-0 fishes were not affected by depth, but did differ among four levels of vegetation cover and these relationships differed among species. Capture efficiencies differed among YAO species (range of species-specific means = 0.17-0.93), but were not affected by vegetation cover or depth. Total abundance of age-0 and YAO fishes (summed across species) captured during the first seine haul were highly correlated with true abundance (age-0 r = 0.96; YAO r = 0.95) but underestimated. Species and age-specific captures from the first seine haul were also highly correlated with true abundance. Finally, proportions of false negative errors of detection were typically higher for YAO than age-0 fishes, and estimated taxa richness and Shannon diversity were correlated with true values, but generally underestimated. Numerous biotic and abiotic factors appear to drive wide variations in capture efficiencies and false negative errors of detection among species, so results from any one study are likely only applicable to particular species. However, seining is an adequate method for investigating within species or total relative abundance (summed across species) trends. Further, seining-based abundance estimates are likely adequate for identifying habitat features associated with relatively high and low catches for a given species. Therefore, seining may be an effective method for comparing these values across sites to gain insights about what types of habitat or locations are most productive for nearshore fishes.