Comparisons between abundance estimates from underwater visual census and catch-per-unit-effort in a patch reef system

Abstract

ABSTRACT: Methods of underwater visual censuses (UVC) and catch-per-unit-effort (CPUE) areboth commonly used to estimate abundance of fish stocks. While each method is subject to certainbiases, in theory they should produce related measures of fish abundance for a specific site at agiven point in time, for species targeted by both methods. We tested relationships between esti-mates of abundance and biomass from UVC and experimental hook-and-line CPUE in a spatiallycomplex coral patch reef system. Fishes targeted by the CPUE method were significantly largerthan those sampled by UVC. Abundance estimates from UVC and CPUE were significantly corre-lated when the data were collected simultaneously—and over small spatial scales (<20 m). How-ever, this correlation was reduced when collection of UVC and CPUE data was separated by eithertime or space. Spatial autocorrelation in the fish community composition was not detected for mostspecies, and abundance estimates were highly variable over time and space. Our results show thatdifferences among monthly sampling periods were responsible for the greatest amount of variabil-ity in the data, and we recommend that abundance estimates should be derived from surveys car-ried out over multiple months to improve accuracy. While the UVC method is useful to detect awide variety of species, some species are more efficiently assessed using CPUE. Development ofcost-effective monitoring programs is crucial to document changes in reef fish populations andsupport the implementation of management regulations that may prevent further degradation ofreef fisheries worldwide.KEY WORDS: Commercial fish abundance · Coral reefs · Fisheries management · Samplingmethod · Spatial autocorrelation · SCUBA survey