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The staff at Mass Audubon Wellfleet Bay Wildlife Sanctuary (WBWS) are the federally designated responders to all stranded sea turtles in southern Massachusetts, including Cape Cod, the Elizabeth Islands, Martha’s Vineyard and Nantucket. In the late fall/early winter, this sea turtle stranding response comprises a massive cold-stun rescue effort for juvenile Kemp’s ridleys (Lepidochelys kempii), juvenile greens (Chelonia mydas), and juvenile and subadult loggerheads (Caretta caretta), many of which wash ashore alive and are transported to the New England Aquarium in Quincy, Massachusetts, to begin rehabilitation. Because sub-adult and adult leatherbacks are gigantotherms, able to maintain internal body temperature higher than surrounding seawater (Frair et al. 1972; Paladino et al. 1990; James et al. 2006), they do not become cold-stunned as do the younger hard-shelled turtles off Massachusetts.

Throughout the summer and early fall, however, almost all stranded sea turtles in this region are dead leatherbacks or loggerheads, with vessel strikes commonly identified as the cause of death. Live or dead entangled turtles, mostly leatherbacks, do not typically wash ashore, as much of the fishing gear in the area is fixed to the bottom. Some carcasses on shore do exhibit signs of previous entanglement, but rarely carry line or gear. Live entangled leatherbacks are disentangled by the Center for Coastal Studies in Provincetown, Massachusetts. WBWS stranding responses to dead sea turtles on the beach include full necropsies when possible, although often a carcass is so decomposed or degraded that a full necropsy cannot be performed.

Figure 1. Female leatherback nesting during the day on Anguilla, 7 April 2009, when she was PIT and flipper tagged. (Photo by S. Wynne).

Figure 2. The Anguilla leatherback as she re-entered the sea at sunset after nesting. (Photo by S. Wynne).

On 11 September 2016, WBWS staff responded to a dead leatherback on Madaket Beach, Nantucket Island, Massachusetts (WBWS #ST2016-74). The carcass was found ventral side up, with at least half of each flipper missing. After removing the plastron, we discovered that the internal organs and carapace were essentially missing, indicating a severe vessel strike had occurred. Given the absence of the carapace, and after a week or more of seawater flushing and predation, neither accurate morphometric measurements nor a full necropsy was possible. Judging from overall size and short tail length, the turtle was recorded as a probable mature female (James et al. 2007). There was no line or gear attached, and no visible wounds or scars indicated previous entanglement (Dwyer et al. 2003; Stelfox et al. 2016; Asmutis-Silvia et al. 2017). Genetics samples were taken from muscle tissue. No flipper tags were present on what was left of the front flippers, but a PIT (Passive Integrated Transponder) tag (Dutton & McDonald 1994) was detected in the right shoulder, #485131373E.

In April 2017, with the help of numerous sea turtle researchers, and through a regional tag database maintained by the University of the West Indies, Barbados, we learned that this leatherback had been PIT and flipper tagged (WC1151 and WC1152) on 7 April 2009 in Anguilla, British West Indies. Anguilla, the most northerly of the Leeward Islands in the eastern Caribbean, has run a turtle tagging program since the early 2000s, led by the Department of Fisheries and Marine Resources (DFMR). Dr. Stuart Wynne, Deputy Director of DFMR, recalls the events of this day back in 2009:

This leatherback is known to have nested three additional times in 2009: on 20 April on St. Maarten, and 1 May and 23 May on St. Croix (C. Lombard and J. Horrocks pers. comm. 2017). This represents a fairly high degree of “straying” by an insular-nesting leatherback (Eckert et al. 1989; Horrocks et al. 2016).

The Anguilla-tagged turtle was the second vessel-struck leatherback fatality responded to by WBWS staff in September 2016. On 9 September, a carcass was reported in the surf in Mashpee, on the south side of Cape Cod, Massachusetts, and this leatherback (WBWS #ST2016-71) also proved to be a reproductive female. As with the Nantucket female, this carcass was highly degraded, including the trailing edge of the flippers, and no flipper tags were present. However, a PIT tag was detected in the left shoulder, #4B12213A0E. She had been PIT and flipper tagged (T51420 and T51494) when nesting at Fishing Pond, eastern Trinidad, in 2010; she nested again at Fishing Pond in 2012 (Kyle Mitchell, pers. comm. 2016).

Figure 3. Carcass of vessel-struck Anguilla-tagged adult female leatherback on Nantucket Island, Massachusetts, USA, on 11 September 2016. (Photo by O. Bourque).

Figure 4. Carcass of vessel-struck Trinidad-tagged adult female leatherback on beach in Mashpee, Massachusetts, USA, on 10 September 2016. (Photo by K. Dourdeville).

Although both PIT-tagged reproductive female leatherbacks were reported in September of 2016, they were likely killed by vessel strikes off Massachusetts in August, judging from the degraded/decomposed condition of the carcasses. August is the peak month of opportunistic leatherback sightings reported to WBWS (Dourdeville et al. In press). Since 2002, WBWS has operated a hotline and website, seaturtlesightings.org, for vessel operators to report sightings of sea turtles off southern New England. The hotline and website have two main goals: (1) to document when and where sea turtles are seen, and (2) to educate vessel operators that sea turtles are present and what they may look like in the water, for the purpose of decreasing vessel strikes. Although these opportunistic sightings are not a survey nor a systematic count of turtles, cannot be corrected for effort, and are skewed toward areas frequented by vessels, the sightings do represent a minimum count of sea turtle/vessel encounters in these highly trafficked waters. Since 2002, the hotline has received over 1,050 credible reports of live leatherbacks, with species identification based on turtle size, reporting party’s description and, ideally, photos or videos. Vessel operators often describe leatherbacks as swimming at or just under the surface, and as basking at the surface on very calm days. The presence of vessels, highly productive shallow depths (Dodge et al. 2014), leatherback surface behaviors, and relatively enclosed bodies of water increase the potential for vessel strikes.

These two reproductive female leatherbacks, killed by vessel strikes off Massachusetts and identified by PIT tags, demonstrate the need for international cooperation in the science and conservation of leatherbacks (Horrocks et al. 2016). The female that nested on three islands (three countries) in 2009, and the inter-season nesting female on Trinidad (2010 and 2012) illustrate the importance of tagging and monitoring efforts by researchers on nesting beaches in the Caribbean (Eckert et al. 1989). They also illustrate the importance of PIT tagging for identification of carcasses that are decomposed or degraded, when flipper tags may be missing, which is often true in northern waters. The deaths by vessel strikes of both females highlight the need for increased attention and protection of this endangered species in northern, foraging waters. From reports of floating vessel-struck or entangled leatherback carcasses, we know that not all these carcasses wash ashore and/or are documented. Although we believe that many inshore dead, floating, vessel-struck leatherbacks eventually wash ashore, we may be significantly under-reporting both vessel strike and entanglement incidents. Regulators face increasing pressure to modify fishing gear and to use seasonal restrictions to minimize leatherback entanglement. Vessel strikes, both recreational and commercial, however, represent a hazard to leatherbacks that is extremely difficult to control or even minimize. More research on leatherback feeding behavior is needed, especially as it relates to vessel strike risk and potential for entanglement in vertical line fisheries in northern waters. Furthermore, to reduce the chances of these unfortunate incidents in the future, increased outreach efforts are needed to raise vessel operators’ awareness of sea turtles and to offer advice as to minimizing risk of striking this endangered, important migratory species.

Acknowledgments. The authors acknowledge leatherback researchers and organizations working on nesting beaches and in northern foraging waters. WIDECAST’s Regional Marine Turtle Tagging Center, managed by Dr. Julia Horrocks at the University of the West Indies, Barbados, has for more than a decade provided complimentary tags, pliers and training to community-based sea turtle conservation programs Caribbean-wide. The Nature Foundation of St. Maarten monitored the Anguilla-tagged leatherback as she nested on St. Maarten, and WIMARCS (Jeanne Garner) and USFWS (Claudia Lombard), monitored her as she nested twice on St. Croix. Nathan Robinson (Leatherback Trust) facilitated our communications with northern Caribbean leatherback researchers. Kate Sampson and Carrie Upite (NOAA, Greater Atlantic Regional Fisheries Office), and Mike James (Canadian Sea Turtle Network) directed us to Kyle Mitchell, of the Trinidad and Tobago National Monitoring Programme, Fishing Pond Environmental Project, who provided details about the Trinidad-tagged turtle. We also thank vessel operators and beach-walkers who report sightings of live, free-swimming sea turtles off New England and who also report carcasses, floating or on beaches. High-Road Marketing and Communications of Rochester, Massachusetts, USA, created the Mass Audubon sea turtle sightings website, seaturtlesightings.org, and donated an upgrade to make the reporting of sightings more user friendly. The authors thank an anonymous reviewer for helpful comments and suggestions on this manuscript.

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