The global expansion of mariculture offers numerous potential benefits, but may also pose a threat to wildlife populations that are attracted to or repelled by mariculture installations. A fish farm that is operated near shore off the west coast of Hawai‘i Island produces kanpachi (Seriola rivoliana), and sits within the known range of several resident species of odontocetes. Almost daily common bottlenose dolphin (Tursiops truncatus) associations with the kanpachi farm have been reported by farm staff, but little information is available regarding the extent or long-term impacts of these associations. We analyzed photos from 20 encounters that occurred between 2007 and 2019 at the farm in the context of over 250 encounters off Hawai‘i Island from between 1987 and 2020. From 67 identifications we identified 28 unique individual bottlenose dolphins that associated with the farm. The rate of discovery of new individuals at the farm is not leveling off. In spite of our limited sample, seventeen of the farm associates were repeatedly sighted at the farm, and six individuals were sighted at or within 5 km of the farm over timespans exceeding ten years. One individual in particular, an adult male with a severe mouthline injury stemming from a fishery interaction, was identified at the farm 10 times, and within 5 km of the farm an additional three times over an 11-year timespan. A crawl model using satellite-tag data from four individuals revealed one individual that may have associated with the farm that was not documented there using photo-identification. Association analyses revealed that farm-associated dolphins are widely distributed throughout the social network, suggesting that the behavior of associating with the farm may continue to spread to other individuals within the population. Bottlenose dolphin aggression involving farm associates towards other species of dolphins (including spinner dolphins (Stenella longirostris), pantropical spotted dolphins (S. attenuata), and false killer whales (Pseudorca crassidens)) appears to be increasing, demonstrating the potential for impacts to multiple protected species. Increased monitoring of bottlenose dolphin associations with the farm and the potential spread of this behavior among the resident dolphin community is needed.
Citation:
Harnish, A.E., R.W. Baird, E. Corsi, A.M. Gorgone, D. Perrine, A. Ward, and E. Sepeta. 2021. Common Bottlenose Dolphin Associations with a Fish Farm in Hawai‘i: Long-Term Associations and Impacts on Other Delphinids. Document PSRG-2021-09 submitted to the Pacific Scientific Review Group, February 2021.
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