Comparisons of abundance of coral-reef fish: Catch and effort surveys vs visual census

Catch per unit effort (CPUE) in fisheries science and visual counts in marine ecology are widely used to provide estimates of relative abundance. Concurrent use of these techniques therefore offers an opportunity for cross-validation. This study compares CPUE to underwater visual census (UVC) estimates of relative species abundance in a multispecies fishery: coral-reef fish in the Solomon Islands. Multivariate analyses showed large differences between CPUE and UVC estimates of abundance. The families Acanthuridae and Scaridae tended to be the primary cause of differences between the techniques when the full assemblage of fish was analysed. However, the relationship between CPUE and UVC did not improve when these families were excluded from the data set and the analyses repeated on families (Serranidae, Lutjanidae, Lethrinidae) caught by the predominant gear type, handlining. This result highlights the point that the choice and use of particular methods require careful consideration in conjunction with the nature of factors being investigated. Many problems of sampling are specific to particular methods and some investigations may benefit from a more pluralistic approach.