Use of sonar transects to improve efficiency and reduce potential bias in visual surveys of reef fishes

A sonar transect method has been found to be a useful alternative to traditional tape-transect methods in quantification of the species richness and abundance of reef fish. No significant difference was found between species richness measured by the methods, and high Jaccard's similarity coefficients were calculated for each site using the two methods, indicating a similar response to fish of both the sonar and tape transects. Abundance estimates of one species only (Chaetodon tricinctus) were greater when the transect tape method was used, probably because fish were being attracted to the divers who deployed the transect tape. Substantial time saving was also noted for the sonar transects, indicating overall that estimating distance using sonar rather than transect tape may enable increased efficiency and accuracy in underwater visual surveys for both ecological and management-related research on reef fishes.