Percorrer por autor "Mason, Katherine Elizabeth"
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- Applying photo-identification to BRUVS to investigate the abundance and drivers of reef sharks in the Cayman IslandsPublication . Mason, Katherine Elizabeth; Erzini, Karim; Gore, MauvisBaited Remote Underwater Video Systems (BRUVS) are an increasingly popular method of surveying marine life such as sharks, due to their ease of use, low cost and non-invasive nature; important when sampling threatened and protected species. BRUVS generate relative abundance indices, most often by counting the maximum number of individuals recorded at one time (MaxN). This study counted the total number of individuals (Nind) per survey using photo-identification to differentiate between sharks. Individuals were also assigned sex and maturity. Relative abundance was compared across the factors associated with each site, in order to gain insight into the drivers of abundance. BRUVS were deployed at 84 sites around Grand Cayman and Little Cayman Islands, during October and November 2018, each for a minimum of 2 hours. Seventy sharks were recorded across 45 sites, belonging to four reef shark species and one unidentified species (identified to genus level). The Caribbean reef shark (Carcharhinus perezi) and the nurse shark (Ginglymostoma cirratum) were the most abundant species. Longer deployment times (120 v 60 min) were found to significantly increase both MaxN and Nind abundance estimates. Significantly more species were recorded with longer time. The mean time for C. perezi and G. cirratum to arrive and to reach Nind was beyond 60 min. Photo-ID allowed 97% of sharks to be identified to species level and 85% of these as individuals. A significantly higher relative abundance of C. perezi were found on Little Cayman but not at inner lagoon sites, whilst there was a higher relative abundance of G. cirratum at deep sites. Depth and zone were significant predictors of species composition, with depth being significant to species and maturity composition. The results demonstrate that the longer deployment time improves abundance estimates and the application of Nind through photo-ID allows for finer-scale analysis. Nind estimates, combined with evaluation of drivers, can be used to explore which factors affect shark abundance of each species, at different maturity stages and for each sex. This can provide valuable information for conservation plans and marine protected area development.