Abstract

Catch per unit effort (CPUE) and underwater visual census (UVC) are often used to produce indices of fish abundance, but each sampling method has inherent biases. We compared CPUE (using hook and line) and UVC abundance estimates (using the stationary cylinder method on SCUBA) in a patch reef system at Glover’s Reef, Belize. UVC and CPUE data were collected at 63 randomly selected sites, and sampling was repeated at a subset of sites to assess temporal variability. The most commonly caught species, yellowtail snapper, porgy, lane snapper, white grunt, and mutton snapper, had occurrence rates of over 25% in both the CPUE and UVC data. For all 5 species, the average size observed in the UVC was significantly smaller than sizes that were caught. Correlations between CPUE and UVC abundance were significant when CPUE and UVC data were collected simultaneous-ly (fishers fishing while divers counting fish, Mantel R = 0.34, p = 0.03), but correlations were not significant when data were collected on different days (Mantel R = 0.07, p = 0.18). These correlations were not improved when spatial effects were accounted for using partial Mantel tests. Further work will evaluate the causes of variability over time and between sampling methodolo-gies. Both CPUE and UVC data are used to inform spatial management plans and to assess effectiveness of existing fishery management regimes. Therefore an understanding of the biases of each method will improve the ability to accurately measure management performance indicators.

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