Disentanglement network data to characterize leatherback sea turtle Dermochelys coriacea bycatch in fixed-gear fisheries

Abstract

To characterize sea turtle bycatch in fixed-gear fisheries in Massachusetts, USA, we analyzed a 15 yr dataset of entanglement reports and detailed documentation from disentanglement operations. Almost all (272) of the 280 confirmed entanglements involved leatherback turtles Dermochelys coriacea. The majority of turtles were entangled in actively fished (96%), commercial (94%) pot/trap gear with unbroken/untriggered weak links, specifically the buoy lines marking lobster, whelk, and fish traps. Most reports came from recreational boaters (62%) and other sources (26%), rather than commercial fishers (12%). Leatherback entanglements occurred from May to November, with peak reporting in August, and included adult males, adult females, and subadults. All entanglements involved the turtle’s neck and/or front flippers, with varying degrees of visible injuries; 47 entangled leatherbacks were dead in gear, 224 were alive at first sighting, and 1 case was unknown. Post-release monitoring suggested turtles can survive for days to years after disentanglement, but data were limited. While the observed entanglements in our study are low relative to global bycatch, these numbers should be considered a minimum. Our findings are comparable to observed numbers of leatherbacks taken in Canadian fixed-gear fisheries, and represent just one of multiple, cumulative threats in the North Atlantic. Managers should focus on strategies to reduce the co-occurrence of sea turtles and fixed-fishing gear, including reductions in the number of buoy lines allowed (e.g. replace single sets with trawls), seasonal and area closures targeted to reduce sea turtle-gear interaction, and encourage the development of emerging technologies such as ‘ropeless’ fishing.

A global review of protected species interactions with marine aquaculture

“…Because they are unable to free themselves, they can drown if held under water and their survival depends on human intervention to remove the lines 237 . These conclusions are validated in an analysis of 15 years of entanglement reports in fixed gear fisheries off Massachusetts, USA 238 . The leatherback entanglements at mussel farms occurred in spat collector lines that are typically not anchored to the substrate.…”

“…All species except for flatback, which is data deficient, are classified as vulnerable, endangered, or critically endangered 236 . To date, there are few reported incidents of sea turtle injuries or mortalities at aquaculture sites 237,238 . Interactions have been reported at mussel farms in Newfoundland, Canada, and Chile, and pearl and seaweed farms in the Philippines.…”

“…The leatherback entanglements at mussel farms occurred in spat collector lines that are typically not anchored to the substrate. Fixed gear that is highly weighted may pose an immediate threat to leatherbacks when they are entangled at depth because they cannot surface to breathe 237,238 …”

High‐resolution diving data collected from foraging area reveal that leatherback turtles dive faster to forage longer

“…In the case of leatherback turtles, expanding high‐resolution behavioral research far beyond nesting beaches to the largely inaccessible, but critically important high‐latitude parts of their foraging range, is essential. Not only does a sizeable component of the northwest Atlantic leatherback turtle population inhabit northern waters for several months each year (James et al, 2005; James & Herman, 2001), but leatherbacks are also vulnerable to entanglement in vertical lines associated with fishing gear in a multitude of areas (Dodge et al, 2022; Doyle et al, 2008; Hamelin et al, 2017; Houghton et al, 2006). Further investigation of leatherback movements and diving behavior in northern waters may therefore be integral to understanding and mitigating leatherback‐fishery interactions.…”

The leatherback turtle (Dermochelys coriacea) and plastics in the Northwest Atlantic ocean: A hazard assessment

“…The most common fishing gear to entangle leatherback turtles consisted of pot gear and trap nets attached by polypropylene lines ( Hamelin et al., 2017 ). Furthermore, a recently published study evaluated sea turtle bycatch in fixed-gear fisheries in Massachusetts from 2005 to 2019 ( Dodge et al., 2022 ). Findings from a 15-year dataset show that 272 out of 280 confirmed cases of sea turtle entanglement involved leatherback turtles.…”