Prevalence of interactions between Hawaiian monk seals (Nemonachus schauinslandi) and nearshore fisheries in the main Hawaiian Islands

Abstract

We determine the prevalence and characteristics of interactions between the Hawaiian monk seal (Nemonachus schauinslandi) and nearshore fisheries in the main Hawaiian Islands and examine impacts to the subpopulation. We documented 139 monk seal–fisheries interactions between 1976 and 2014: 132 hookings typically involving large circle hooks accompanied by slide-bait rigging, and 7 gill-net entanglements. We individually identified 297 monk seals between 1988 and 2014 and recorded that 83 (28%) of these had at least one documented hooking or entanglement. Most individuals were aged two years or younger and a quarter of them were hooked or entangled multiple times. Documented fisheries interactions typically occurred at a monk seal’s natal island and most frequently on Kauai and Oahu. Fisheries interaction was directly implicated in 11 monk seal deaths and was slightly higher in frequency than other known mortality factors. The proportion of monk seals alive one year after a documented fisheries interaction varied by age class and ranged between 76% and 84%. Survival one year later for monk seals with a documented fisheries interaction versus matched controls (all age classes combined) was not significantly different. Nonetheless, fully understanding the scale and impacts of fisheries interactions, as well as mitigating these impacts, is important if the monk seal population of the main Hawaiian Islands is to maintain a positive growth trajectory.