Long‐term associations of common bottlenose dolphins with a fish farm in Hawaiʻi and impacts on other protected species

Abstract

The global expansion of mariculture offers numerous potential benefits but may also pose a threat to wildlife populations. There is currently only one commercial finfish mariculture facility in Hawaiʻi, a nearshore kanpachi (Seriola rivoliana) farm off the west coast of Hawaiʻi Island. This farm lies within the range of several resident odontocete species, and almost daily common bottlenose dolphin (Tursiops truncatus) associations with the farm have been reported since 2007. We analyzed photographs of 35 bottlenose dolphin groups at the farm sighted between 2008 and 2021 in the context of 20 years of survey effort and extensive community science contributions from Hawaiʻi Island. Thirty‐six bottlenose dolphins were identified associated with the farm, representing almost one‐quarter of the estimated total population size. The discovery rate of new individuals at the farm indicates this is a conservative estimate of the total number of individuals associating with the farm, and social network analysis suggests that associations may continue to spread within the population. We also found a high frequency of farm associated bottlenose dolphins showing aggression towards several other species of dolphins, demonstrating impacts to multiple protected species.

Aquaculture related humpback whale entanglements in coastal waters of British Columbia from 2008–2021

“…Scavenger fish also aggregate around fish farms because of nutrients in the water from leftover feed, feces, and organic matter removed from the nets, and the shelter provided by the equipment [ 24 , 25 ]. The abundance of both farmed and wild fish in a localized area appears to attract marine mammals, especially otariids (sea lions and fur seals) [ 17 , 18 , 26 , 27 ], but also odontocetes [ 28 ], benthic invertebrates and birds [ 29 ].…”

“…In other countries, associations between common bottlenose dolphins and aquaculture facilities are reported. For example, direct predation on production fish has been recorded in Hawaii where at least one dolphin has performed actions that result in fish escapement from cages, on more than one occasion [ 28 ]. These interactions have been documented since 2008 and include about one quarter of the Hawaii Island Resident dolphin population, suggesting that associating with fish farms is a successful foraging strategy.…”

Quantifying the abundance and survival rates of island-associated spinner dolphins using a multi-state open robust design model

“…Recent observations suggest that spinner dolphins less frequently use a previously preferred resting bay off the Kona Coast where they experienced the highest exposure rates to human activity 35 , 36 . However, this change in habitat use may be linked to the construction of aquaculture facilities outside the bay or aggression from bottlenose dolphins that frequent these facilities 37 . In response to concerns pertaining to the long-term impacts of tourism activities on spinner dolphins in Hawaiʻi, NOAA implemented federal legislation in 2021, prohibiting humans and boats from approaching spinner dolphins within 50 yards (45 m) within two nautical miles from shore (NOAA, 86 FR 53818).…”