Relationships between hydroacoustic derived density and gill net catch: Implications for fish assessments

In this paper, we describe our assessment of whether gill nets and hydroacoustics provided similar inferences on the local abundance of fishes and whether gill net catch could be used to predict acoustic-derived abundances. We collected hydroacoustic and gill netting samples from a restricted area of large hydropower reservoir in the southeastern United States. We used mixed linear models in an information theoretic framework to model acoustic-derived abundances as a function of gill net catch and a variety of biological and environmental covariates. Overall, gill net catch was a poor predictor of acoustic-derived abundance and the best model only accounted for 39.6% of the within year variation. In fact, a gill net catch (e.g., 100 fish/net) was approximately equally likely across several orders of magnitude in fish abundance. This result suggests that gill net catch was unable to reliably discern substantive changes in fish abundance. Consequently, the most appropriate role for gill nets in fisheries research assessments may be to: (1) supplement hydroacoustic data by providing information on species composition and fish sizes and (2) provide information on metrics other than fish abundance, such as fish growth and condition.