By Nadine Pinnell and Jamie Myers
If you think of all the animals you could see out on the water this summer, large ancient reptiles probably don’t even cross your mind. However, a few people every year are lucky enough to see a leatherback sea turtle (Dermochelys coriacea) in B.C. waters. Last year, the Sightings Network received nine reports of leatherback sea turtles in B.C. At up to 6 feet in length, leatherbacks are difficult to mistake for anything else. They have a distinctive ridged, teardrop-shaped carapace made of connective tissue and small bony plates rather than a hard shell or scales like other sea turtles.
Globally, leatherback turtles are a critically endangered species with their numbers only a quarter of what they were 20 years ago. The world population is estimated at 30,000 to 40 000 nesting females in the Atlantic, Pacific, and Indian Oceans. Scientists suggest that Pacific leatherback populations in particular are on the verge of extinction. This makes the survival of individual turtles even more important to the population as a whole, which is one reason that the Vancouver Aquarium Marine Science Centre began collecting sightings of sea turtles three years ago. By learning more about where and when these turtles use B.C. waters, we can ensure that they are not encountering threats to their survival here.
In Canada, leatherback turtles are listed as “endangered” under the Species at Risk Act. A recovery team of experts, including personnel from the Vancouver Aquarium, was formed to prepare a recovery strategy and action plan for Pacific leatherback turtles in Canadian waters.
Leatherback sea turtles are the widest-ranging marine reptiles, with some of them migrating more than 11 000 kilometres every year. They have been sighted as far north as Alaska and the North Sea and as far south as Chile and New Zealand. These far-ranging habits are made possible by their ability to regulate their body temperature in order to survive in colder waters. Dark skin colour, large body size, a thick layer of fat, and the ability to regulate their blood flow to reduce heat loss all allow leatherbacks to maintain a body temperature as much as 18°C higher than the ambient temperature.
Leatherbacks entering colder waters are likely there in search of jellies, their major prey. They seem to be attracted to upwelling areas where their prey are abundant as well as to boundaries between warm and cold waters; however, much about their migratory patterns is still left to be explained.
Think Nuno Gomes’ record-breaking scuba dive to 318 metres earlier this year was impressive?
Leatherback turtles have been tracked diving to 640 metres, the deepest dive yet recorded for a reptile, and unpublished data suggests that they may occasionally go deeper than 1000 metres. Despite their record-holding status, leatherbacks generally dive at depths less than 200 m when following their main prey of gelatinous zooplankton and jellies. This diet is 97 percent water so the turtles would likely waste too much energy trying to catch such low-calorie prey at greater depths. It is thought that the deep dives that have been recorded for tagged turtles are a flight response to predators or passing boats.
Every few years, adult female leatherbacks return to nesting beaches in tropical waters to lay eggs. Once the eggs have been laid, the female returns to the water, leaving her offspring to find their way to the water and out into the open ocean themselves once they hatch. In the Pacific, leatherback nesting beaches can be found in Mexico, Costa Rica, Indonesia, and Malaysia. Nesting habitat loss due to tourism and development, egg poaching, and predation have all affected the nesting success of leatherback populations in these areas, contributing to the decline of the Pacific population.
While out in the open ocean, leatherbacks face several conservation threats.
Longline fisheries targeting tuna or swordfish regularly catch sea turtles and other marine species as bycatch. Scientists estimate that commercial long-line tuna, swordfish, and other fisheries in the Pacific caught 1000 and 3200 leatherback sea turtles in 2000 alone. Changing the types of hooks used in these fisheries could provide a partial solution to the problem. A recent year-long WWF study in Ecuador showed that using circle-shaped rather than J-shaped hooks in tuna and mahi-mahi longline fisheries reduced the number of sea turtles hooked by 88 and 37 percent respectively. Until alternate fishing gear such as circle hooks are in widespread use, the most effective way to help turtles is to avoid buying seafood caught using fishing methods that place leatherbacks at risk (see sidebar for more information). Other proposed solutions include turtle conservation areas and mobile no-fishing zones that move with the turtles.
Marine debris also poses problems for turtles. Their choice of prey leaves them vulnerable to mistakenly ingesting debris such as plastic bags that resemble jellies; attempts to eat such “prey” generally result in the turtle’s death. An action as simple as properly disposing of garbage while on or near the water benefits sea turtles as well as many other species of marine life.
How YOU can help!
1. Report any sea turtles you see in B.C. or offshore waters to the Cetacean Sightings Network here or by calling 1 866 I SAW ONE (1-866-472-9663).
2. Choose Oceanwise for sustainably-caught seafood when you’re at the grocery store or visiting a restaurant.
3. Keep garbage out of the ocean. Properly dispose of your trash and plastic bags while boating. Participate in the TD Great Canadian Shoreline Cleanup.
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