Quantifying the efficacy of a spatio-temporal management intervention on human-dolphin interactions in Hawai’i

Since the 1980’s, concerns have been raised about the extent of water-based tourism targeting spinner dolphins (Stenella longirostris) in their resting habitat off Big Island of Hawai’i. In 2010, spinner dolphins associated with the Big Island were defined as a unique stock and were also identified as one of the most vulnerable to anthropogenic disturbance. The National Oceanic and Atmospheric Administration is currently considering a management intervention to reduce the number and intensity of human-dolphin interactions by implement time-area closures in critical habitat. To measure the effectiveness of this mitigation approach a Before-After-Control-Impact (BACI) design is being employed to asses the local abundance, distribution and behaviour of spinner dolphins in four resting bays before and after the implementation of time-area closures. Systematic boat-based photographic identification surveys have been carried out continuously over the past year following Pollock’s Robust Design (Primary period: each month; Secondary Period: 2-4 consecutive days in each of the four bays). Of the 96 surveys undertaken over 850 hours, spinner dolphins were observed on 43 (45%) occasions with group sizes ranging from 6 to approximately 250 dolphins. Preliminary abundance estimates over five primary periods ranged between 205 (SE ± 18; 95% CI = 176 – 249) and 446 (SE ± 73; 95% CI=329 – 621) spinner dolphins frequenting the study area. The precision of these preliminary abundance estimates will be tested over the next 3 to 5 years of continued data collection. In addition, passive acoustic loggers have been deployed in each bay, recording 30 seconds every 4 minutes with data collected continuously. These acoustic data allow for cross-validation with photographic survey records, and the method of deployment will provide an index of the regularity of dolphin presence in each bay before and after the implementation of time-area closures