Abstract

Decompression sickness (DCS) has recently been described in loggerhead turtles (Caretta caretta) following fisheries bycatch in trawls and gillnets.¹ A proposed mechanism is catecholamine-induced increased sympathetic tone at capture reversing a physiologic bradycardia and right-to-left cardiac shunt that minimizes blood flow through the lungs during diving. Increased blood flow through pressurized lungs may allow increased dissolved nitrogen in the blood, which followed soon after by unregulated ascent may lead to formation of gas emboli (GE). Presence of GE need not result in clinical DCS, depending on severity (amount) and distribution. Main factors that may affect GE formation in bycaught sea turtles include water temperature, speed of ascent, body size, turtle species, fishing technique and depth and soaking time of the gear. Although suspected to occur in fisheries bycatch elsewhere, it has thus far been reported only from Spain, Italy and Brazil, from nets set or hauled at depths greater than 10 m. Here we present cases of three green turtles (Chelonia mydas) entrained in a hopper dredge conducting winter maintenance of a shipping channel at depths of 10–13 m. Turtle weights ranged from 2.90–4.95 kg. All were reported as live takes by an on-board observer and transferred to the North Carolina Sea Turtle Stranding and Salvage Network for transport to a rehabilitation facility. Two sustained major blunt force whole-body trauma from passage through the dredge, and died within 24h despite supportive care, including antibiotics, anti-inflammatories, fluids, and in one case normobaric oxygen. The third case continues to recover. The two mortalities had radiographic and/or ultrasonographic evidence of GE formation, and on fresh necropsy had mild to moderate GE in mesenteric vessels, the right atrium, and kidneys. Histopathology confirmed that tissues were in a good state of preservation without evidence of putrefaction as a cause of intra- and extravascular gas. Gas embolism was not histologically evident, likely due to dissipation during dissection and fixation. Cause of death may have had more to do with massive tissue trauma from passing through the dredge mechanism with heavy sediment, but GE could have complicated recovery. The surviving case sustained less severe trauma and had only equivocal evidence of GE. Hopper dredge entrainment is an additional potential cause of GE in sea turtles.

Acknowledgments

We thank Lori Westmoreland, Emily Christiansen, Heather Broadhurst, and Sarah Finn for assistance with these cases, and volunteers at the Karen Beasley Sea Turtle Rescue and Rehabilitation Center for dedicated care of the turtles.

* Presenting author

Literature Cited

1.  García-Párraga D, Crespo-Picazo JL, Bernaldo de Quirós Y, Cervera V, Martí-Bonmati L, Díaz-Delgado J, Arbeo M, Moore MJ, Jepson PD, Fernández A. 2014. Decompression sickness ('the bends') in sea turtles. Dis Aquat Organ. 111:191–205.