Validating the use of baited remote underwater video surveys for assessing the diversity, distribution and abundance of sharks in the Bahamas

Baited remote underwater video surveys (BRUVS) are a novel, non-invasive method of generating relative abundance indices for a number of marine species, including sharks. This technique has become increasingly prevalent in shark ecology literature, but has yet to be formally validated against more traditional shark survey methods. BRUVS and longline surveys were conducted over 4 seasons from summer 2008 to spring 2009, in 3 habitat zones in the waters off Cape Eleuthera, The Bahamas. By the end of the project, both techniques generated similar values of species richness; however, longline surveys reached these values faster and with fewer replicates than BRUVS. Overall there was a significant positive correlation of relative abundance between the 2 survey techniques, but when analysed on a species-by-species basis, correlations were not statistically significant for the less abundant species. This suggests a threshold level of abundance, below which relative abundance estimates generated by the different survey techniques do not agree. In addition, this study identified shortcomings in the ability of BRUVS to accurately identify the species, size and sex of individuals captured on video due to the variable behaviour of the sharks in front of the camera; however, technological improvements incorporated into contemporary studies are identified which might improve data quality. BRUVS offer a non-invasive alternative to longline surveys for monitoring broad trends in the relative abundance of sharks, although in the format tested in this study they may lack the resolution required to approach finer scale, intra-species studies.