Marine debris impacts on Hawaiian green sea turtles (Chelonia mydas): High prevalence of hook-and-line fishing gear in strandings

Stranding data are critical for monitoring threats to sea turtles. By analyzing four decades of green turtle (Chelonia mydas) strandings from the Main Hawaiian Islands, we elucidate temporal and spatial trends. In Hawai'i, fibropapillomatosis (FP) has been the dominant threat for stranded turtles since records began in 1982. In the last decade (2010-2019), FP constituted on average 25 % of stressors in stranded turtles, followed by fishing lines (22 %), hooks (8 %), shark predation (5 %), boat strikes (5 %), and net entanglements (3 %). As of 2016, fishing line injuries constitute the most common primary threat. Turtles injured by lines and hooks were often found and released alive (hooks: 86 % alive, lines: 64 % alive), underscoring the importance of timely reporting and response. O'ahu was found to be the main hotspot for hook-and-line strandings, while there was more variation across islands for the other stressors. Spatial predictions highlighted areas without prior stranding observations, suggesting that some strandings may go undetected. As the main hotspot for fishing line strandings, we modelled the presence of derelict line around O'ahu using data from in-water debris cleanup efforts; we found that (1) derelict fishing line was positively associated with shore access points and boat harbors and (2) negatively associated with human population density. The increase in strandings with fishing line could be a result of the recovering turtle population and their overlap with year-round coastal fishing activities. Our findings emphasize the need for sustained cleanup efforts and measures to reduce fishing gear losses and interactions with non-target species.