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

Kl Dodge,S Landry,K Sampson,D Sandilands,Cj Innis,B Lynch,B Sharp

doi:10.3354/esr01173

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.

Highlights

Incidental capture, or bycatch, of non-target species in fisheries gear is a critical global conservation issue (Žydelis et al 2009, Lewison et al 2014)
Leatherback nest numbers have declined across the majority of monitored nesting beaches within the Northwest Atlantic
To explain these declining trends, one hypothesis points to a potential increase in the number of lethal leatherback−fisheries interactions (Northwest Atlantic Leatherback Working Group 2018)

Summary

Introduction

Incidental capture, or bycatch, of non-target species in fisheries gear is a critical global conservation issue (Žydelis et al 2009, Lewison et al 2014). (Wallace et al 2010, Lewison et al 2014, Casale et al 2017), with the exception of large whales in pot/trap gear (Johnson et al 2005, Knowlton et al 2012, Jannot et al 2021). Since bycatch events are usually rare relative to overall fishing effort (Wallace et al 2013), it can be challenging to implement adequate fishery observer coverage, especially in large-fleet fisheries. Observer-based data collection may be inadequate depending on how the gear is fished (e.g. tended vs untended fisheries)

Methods

Results

Conclusion