Special to Expositor
BOSTON- When doing autopsies of large marine animals, New England Aquarium veterinarians and biologists commonly find sea turtles and whales that have died due to either entanglement in marine gear or from trauma from being struck by vessels or from gastrointestinal blockage due to the ingestion of plastics. To their consternation earlier this week, they did a post-mortem examination on a 400 pound leatherback sea turtle that had fallen victim to all three, human-caused hazards – something that they could not recall ever seeing before.
Despite its large size, this endangered sea turtle was a juvenile and had been a summer and autumn visitor to New England waters feeding on sea jellies offshore. A University of Rhode Island research vessel first sighted its black-shelled carcass late last week as it was floating in Cape Cod Bay. On Sunday, the bloated body of the leatherback had washed up on to Sandy Neck Beach in Barnstable. Later that day, it was transported to the Aquarium’s sea turtle hospital in Quincy, MA for necropsy.
Monday morning, the Aquarium’s head veterinarian Dr. Charles Innis led a team to try to determine its cause of death. From the initial external exam, heavy abrasions and lacerations could be seen around the turtle’s front flippers, which is a telltale sign of entanglement with a vertical rope in the water. Such lines usually extend from a surface buoy to a boat mooring anchor or fixed fishing gear like lobster pots.
Swimming In the low light of the region’s plankton rich waters and among a gauntlet of vertical lines, large sea turtles all too commonly get spun around upon encountering such a rope and then often get the line fully wrapped around their flippers or head. Being a reptile and an air breather, sea turtles must occasionally surface. If not lucky to escape or to be spotted by boaters, these incredibly strong swimmers will eventually and ironically drown.
What was also quite visible was some major deformity at the center and top of the young male’s shell. X-rays showed that the turtle had extensive fractures of its shell and vertebrae. Remarkably, these injuries had been healing fairly well over the past several months. Dr. Innis estimated that the leatherback was probably struck by a vessel in the early summer and had survived and even thrived as the Aquarium’s biologists found a robust layer of fat on the carcass as it apparently was still able to forage well over the remainder of the summer and fall.
Leatherbacks, true to their name, do not have a hard, bony external shell. Instead, they are covered with a mostly black, thick, leather-like hide. The very dark coloration makes them hard to see against the dark green waters of the northwest Atlantic. When feeding on sea jellies at the surface, recreational boaters, particularly south of Cape Cod, often hit them.
As the team examined organs for evidence of disease, they found three plastic objects in the animal’s stomach. The largest was a three-foot by 1 foot piece of plastic sheeting commonly found in building supplies. Smaller items included a sandwich bag and a hard candy wrapper. These types of highly durable plastic items when blown on to the sea often float on the surface in an undulating manner similar to sea jellies. Despite the size of these items, they had not yet caused a full intestinal blockage, which could have eventually killed the animal. The smaller items could have been passed, but staff was quite certain that the 3 foot square sheet of plastic would have never left the sea turtle.
Despite its other life threatening conditions, the final necropsy conclusion was that this young leatherback had died due to injuries consistent with entanglement in marine gear. In one summer of its short life, this giant, highly endangered sea turtle had encountered a triple threat of human-caused hazards that keep this 65 million year old leatherback species teetering at the brink of extinction.