External Scarring as an Indicator of Fisheries Interactions with Bottlenose (Tursiops truncatus) and Pantropical Spotted (Stenella attenuata) Dolphins in Maui Nui, Hawai‘i

In Maui Nui, Hawai‘i, limited information is available regarding the impact of fisheries interactions on two island-associated populations of common bottlenose (Tursiops truncatus) and pantropical spotted (Stenella attenuata) dolphins. To quantify the number of individuals with evidence of fisheries interactions, this study examined images of bottlenose and spotted dolphins’ dorsal fins, mouthlines, and bodies that were photographically identified during survey efforts from 1996 to 2020. Our results reveal that 27% of the 255 identified bottlenose dolphins and 13% of the 374 identified spotted dolphins displayed one or more fishery gear-related scars. These data suggest that fisheries interactions may pose a serious threat to the population of bottlenose dolphins and is a concern for spotted dolphins in Maui Nui, Hawai‘i. Our methodology of reviewing above- and underwater footage for mouthline and body images increased scar-detection rates by 51 and 40% for bottlenose and spotted dolphins, respectively. We recommend that future surveys expand dorsal fin photo-identification efforts to collect additional above- and underwater images of animals’ mouthlines and bodies when in the field. In conjunction with the apparent decline in the Maui Nui bottlenose dolphin population, our findings highlight the need for further investigation regarding the level of impact fisheries interactions have on the status of these populations.