Incidental capture of leatherback sea turtles in fixed fishing gear off Atlantic Canada

Abstract

1. Incidental capture in commercial fishing gear is a threat to many populations of marine megafauna, including sea turtles. While research has largely focused on pelagic longline impacts on sea turtles, fixed-gear fisheries are a significant, historically understudied source of injury and mortality.2. The present study assesses the interaction of endangered leatherback sea turtles (Dermochelys coriacea) with fixed-gear fisheries in high-latitude seasonal foraging habitat where sub-adult and adult turtles aggregate.3. Records of leatherback-fishery interactions (n = 205) were compiled from databases of publicly-reported sea turtle sightings in Atlantic Canada (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) to identify the spatiotemporal distribution of these events; to identify corresponding fisheries and gear types; and to describe the mechanics and outcomes of entanglements in fixed gear. 4. Most reports came from coastal Nova Scotia (n = 136) and Newfoundland (n = 40), with reporting rates peaking in the mid-to-late 2000s. The majority of entanglements were reported during the summer months of July and August when leatherbacks are seasonally resident and several fisheries are active in continental shelf waters.5. Entanglements were most commonly reported in pot gear (e.g. snow crab, lobster, whelk) and trap nets (e.g. mackerel), reflecting extensive use of polypropylene lines distributed in the upper water column where leatherback foraging activity is concentrated. 6. Given reporting biases and uncertainty regarding post-release survivorship, entanglement mortalities should be considered a gross underestimate of true mortality rates.7. This study highlights both the importance of looking beyond pelagic longlines to evaluate leatherback interactions with fixed-gear fisheries in high-use continental shelf foraging habitat, and of involving the fishing industry in developing mitigation measures to reduce entanglement rates and associated turtle mortality.

Prevalence of visible injuries to leatherback sea turtles Dermochelys coriacea in the Northwest Atlantic

“…What is clear, however, from visible injuries sustained through probable fishery interactions, is that lines, ropes, nets, and hooks present a regular hazard. This evidence for rope, line, and net interactions is consistent with patterns of leatherback− fishery interaction derived from reporting networks (rope, line; Hamelin et al 2017) and fisher interviews (artisanal gill nets ;Lum 2006), informing understanding of where research on fishing gear design and practices to mitigate leatherback bycatch might be effectively directed. Most turtles with observed line injuries appeared to exhibit normal movement and range of motion in affected body parts, although the extent of scaring in some cases suggests this may not have always been the case at the time of injury.…”

“…These results are consistent with growing evidence positing fisheries bycatch as one of the principal direct threats facing leatherbacks (Lewison et al 2004, Donlan et al 2010, Wallace et al 2010). In addition, the large proportion of leatherbacks with injuries indicative of entanglement highlights the threat that fixed gear , Hamelin et al 2017) and gill nets (Lum 2006, Lewison & Crowder 2007 pose to this species. Evidence of suspected hooking among our sample was also high, consistent with the regularity with which this species interacts with pelagic longline fisheries (Lewison et al 2004).…”

“…Entanglement in fixed fishing gear has been posited as a principal anthropogenic threat to leatherbacks in waters off Atlantic Canada (Hamelin et al 2017), while entanglement in gill nets is a leading cause of injury and mortality for the breeding population in Trinidad (Lum 2006). Turtle−fishery interactions in both regions from these sources result in similar injuries (e.g.…”

A Summary of Sea Turtles Released from Rescue and Rehabilitation Programs in the United States, with Observations on Re-Encounters

“…It is possible that various communication barriers result in failed reporting in some cases (e.g., investigator motivation, database errors, language, time, etc. ), and that the perception of negative bias may inhibit reporting of some types of encounters (e.g., fisheries interactions; Hamelin et al 2017). Data-sharing between various groups that intersect with tagged sea turtles (e.g., RRRR facilities, in-water research groups, nesting beach monitoring groups, STSSN) may not be complete.…”

TurtleCam: A “Smart” Autonomous Underwater Vehicle for Investigating Behaviors and Habitats of Sea Turtles

“…While there is evidence that sea turtles can modify their behavior based on variable environmental conditions Schofield et al, 2009), there is currently little information on behavioral adaptations relative to transient human activities. Sea turtle mortalities in coastal habitats frequently show evidence of human interaction that suggests they are unable to avoid some anthropogenic threats, including vessel strike (Hazel and Gyuris, 2006;Tomás et al, 2008), fishery interactions (Peckham et al, 2007;Casale et al, 2010;Hamelin et al, 2017), and debris ingestion (Bjorndal et al, 1994;Mrosovsky et al, 2009). Furthermore, some turtle behaviors (e.g., shallow water diving, affinity for nearshore habitat) may actually exacerbate risk (Hazel et al, 2009).…”