Abstract
Methods of underwater visual censuses (UVC) and catch-per-unit-effort (CPUE) are both commonly used to estimate abundance of fish stocks. While each method is subject to certain biases, in theory they should produce related measures of fish abundance for a specific site at a given point in time, for species targeted by both methods. We tested relationships between estimates of abundance and biomass from UVC and experimental hook-and-line CPUE in a spatially complex coral patch reef system. Fishes targeted by the CPUE method were significantly larger than those sampled by UVC. Abundance estimates from UVC and CPUE were significantly correlated when the data were collected simultaneously—and over small spatial scales (<20 m). However, this correlation was reduced when collection of UVC and CPUE data was separated by either time or space. Spatial autocorrelation in the fish community composition was not detected for most species, and abundance estimates were highly variable over time and space. Our results show that differences among monthly sampling periods were responsible for the greatest amount of variability in the data, and we recommend that abundance estimates should be derived from surveys carried out over multiple months to improve accuracy. While the UVC method is useful to detect a wide variety of species, some species are more efficiently assessed using CPUE. Development of cost-effective monitoring programs is crucial to document changes in reef fish populations and support the implementation of management regulations that may prevent further degradation of reef fisheries worldwide.
