Bringing the right fishermen to the table: Indices of overlap between endangered false killer whales and nearshore fisheries in Hawaiʻi

Abstract

Incidental bycatch in fisheries is a pressing conservation issue for marine mammal populations across the globe. However, the ability to detect and therefore mitigate this issue is challenging for several reasons. Fishermen are unlikely to voluntarily report bycatch due to fear of penalization or apathy towards it. While fisheries observer programs are sometimes in place to record bycatch, many fisheries have no observers. In Hawaiian waters there are no observer programs in nearshore fisheries, yet interactions with fisheries are likely the greatest threat to the endangered main Hawaiian Islands insular population of false killer whales (Pseudorca crassidens). We assess spatiotemporal overlap between false killer whales and nearshore fisheries in Hawai‘i to identify fisheries and regions where interactions are most likely to occur. Interactions with fisheries was cited as the greatest threat to this population's viability as a result of growing evidence over recent decades. We used false killer whale location data from 38 satellite tag deployments (2007–2018) and commercial fishery catch logs from a corresponding period to develop fishery overlap indices (FOIs) from a perspective that should reflect the experience of local fishermen. The area off Kona has the highest levels of fishing effort, but a low FOI, while high FOI values (up to several thousand times higher than Kona) were found off O‘ahu, Moloka‘i, Maui, Lāna‘i and the north end of Hawai‘i. Our findings provide direction for where efforts should be focused to effectively monitor and mitigate bycatch for this endangered population of false killer whales.