Visually Estimating Fish Density at Artificial Structures in Lake Anna, Virginia

Abstract

Four artificial structures in Lake Anna, Virginia, were chosen to develop and refine a sampling technique designed to assess the effectiveness of structures in attracting fish. Several underwater observation techniques were tried before one suited to the prevailing restrictive and low‐visibility conditions was devised and applied to the four structures in summer and autumn 1988. Three consecutive fish counts were made at nine sampling locations per structure. Bluegills Lepomis macrochirus less than 15 cm in total length dominated counts at all structures and were used to evaluate the sampling technique, Counts of bluegills made immediately after divers descended were significantly (P < 0.05) lower than counts made 3 and 5 min after descent. Differences among initial and subsequent counts appeared related to bluegill adaptation to divers and diver adaptation to low light levels underwater. The cumulative mean number of bluegills counted over nine sampling locations per structure and the associated variability tended to stabilize by the time fish at the sixth or seventh location had been counted. Sampling seven locations per structure was sufficient to obtain an index of bluegill density. Differences in bluegill density from summer to autumn were apparent at two structures that were more than 4 years old but not at two 6‐month‐old structures.

Artificial macrophytes as fish habitat in a Mediterranean reservoir subjected to seasonal water level disturbances

“…Despite being recognized as one of the most effective methods to survey structurally complex habitats (Seaman and Sprague 1991), it also is possible that visual censuses may have contributed at some level to the prevalence of small fishes in the artificial macrophytes in Boadella Reservoir. Although not observed in this study, Graham (1992) and Hayse and Wissing (1996) previously reported that fish [150 mm TL often moved further way from artificial structures as divers came closer (i.e. fright response), indicating that further research is necessary to elucidate the importance of that factor on fish use analysis of submerged habitats.…”

Evaluating the Effectiveness of Artificial Fish Habitat Designs in Turbid Reservoirs Using Sonar Imagery

“…When performing visual counts on artificial fish habitats, Graham (1992) found that fish dispersed by divers would return in 3-5 min. Therefore, after DIDSON deployment, we waited 5 min before recording fish counts.…”

Variable Effects of Habitat Enhancement Structures across Species and Habitats in Michigan Reservoirs

“…In general, the average number of individuals and species attracted increases with the structural complexity achieved by increasing the volume, size, and surface area of habitat enhancement structures (Wickham et al 1973;Rountree 1989;Graham 1992). Further, fish abundance varies with structure interstice size (the space within structures) in a complex fashion (Wege and Anderson 1979;Johnson et al 1988;Lynch and Johnson 1989;Walters et al 1991).…”