A Comparison of Two Standardized Gillnetting Protocols for Assessing Fish Community Structure of Boreal Lakes

Standardized fish community surveys are an essential tool for fisheries management and research but the interpretation of community structure may depend on the methods used.  The NORDIC and Broad-scale Monitoring (BsM) protocols are widely used for fish community surveys on northern lakes. Both protocols require standardized, multimesh gill net sets with sampling effort scaled to lake area and depth.  These protocols differ in several ways including gear configuration, method of deployment, and the depth distribution of sampling effort.  We compared measures of fish community composition derived from NORDIC and BsM surveys conducted in a paired-comparisons design on 23 Boreal Shield ecoregion lakes.  Principal components analyses (PCA) of species catch-per-unit-effort (CPUE) indicated significant differences between protocols in estimating community composition, and preliminary results indicate that NORDIC surveys provide higher estimates of species richness and diversity.  Analyses of differences between protocols in estimates of size and age compositions are ongoing.  Our results to date suggest that researchers and resource managers need to carefully consider the protocol used when interpreting fish community survey data.