Using photo identification to assess demographics and fishery interactions of oceanic whitetip sharks Carcharhinus longimanus in the main Hawaiian Islands Marine Ecology Progress Series

Global declines in oceanic whitetip shark Carcharhinus longimanus populations have resulted in international protections and a ‘threatened’ listing under the United States Endangered Species Act in 2018. Despite having international regulations on catch and trade of C. longimanus populations, large gaps remain in our understanding of their basic biology, ecology, and population structure. The main Hawaiian Islands (MHIs), USA, are thought to be a biologically important area for central Pacific C. longimanus, where commercial and recreational fishers have reported seasonal spikes in abundance and interaction rates. Using photo-identification of dorsal fin patterns, this study describes population demographics, reproductive activity, fishery interactions, and associative behaviors of C. longimanus around the MHIs. From 2006 to 2024, 383 individuals were identified, with 42 individuals sighted more than once. The highest number of encounters was recorded during the spring (March-May) and the lowest in winter (December-February). The sex ratio was ~2:1 females:males (females n = 241: males n = 108), and 42 females (17.4%) had visible mating scars while 87 females (36.1%) had distended abdomens, possibly indicating pregnancy. Fishery interactions were observed on 157 individuals (26.3% of all encounters), and 46.8% of sharks observed in this study were found within 0.4 km of a fish aggregation device, while 19.2% were found in association with marine mammals. These results provide baseline information on C. longimanus around the MHIs and are necessary to inform conservation and management efforts for this protected species throughout the central Pacific Ocean. Grant no. NA21NMF4320043