Four Decades of Green Turtle (Chelonia mydas) Strandings on Hawai'i Island (1983-2022): Causes and Trends.

Abstract

The Hawaiian population of green turtles (Chelonia mydas) has increased since Federal and State protections were implemented in the mid 1970s, and reported stranding events have also increased. This study analyzed Hawai'i Island data: stranding location, date, size, sex, presence/absence of tumors, stranding status, and cause of stranding. A total of 754 stranded green turtles was reported from 1983-2022: 379 stranded on the east (windward) coast of Hawai'i Island and 375 on the west (leeward) coast. Strandings peaked in 2011 and 2018 and were highest from March to August. The most common known cause of stranding was hook-and-line fishing gear (21.4% of total strandings), followed by fibropapillomatosis (7.2%), human take (4.4%), miscellaneous (3.7%), boat impact (3.3%), shark attack (3.2%), and net (2.1%); however, 54.8% of strandings had no known cause. Statistical modeling did not provide convincing evidence of temporal changes in the distribution of strandings across three consolidated cause categories: human-caused; predation, disease, and weather; and unknown. Stranded turtles on east Hawai'i Island had a higher frequency of fibropapillomatosis, whereas west Hawai'i stranded turtles showed higher incidence of shark attacks. These results provide the first comprehensive analyses of stranding data from Hawai'i Island and provide information that can inform resource managers, policy makers, and the public about the various types and magnitudes of impacts, anthropogenic and natural, to green turtles so that mitigation measures can be put into practice. Our findings allow for comparison with other green turtle populations worldwide.