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Book Review

Turtles of the North – Canadian Fishermen Help Scientists Study the Cryptic Leatherback

 

For most people, sea turtles evoke visions of white sand beaches, crystal clear waters, and boozy fruity drinks, the embodiment of a tropical vacation. They don’t usually bring to mind the rocky coasts of Cape Breton or the cold waters of the North Atlantic.

In the fishing grounds of Atlantic Canada, June to October is “turtle season”, the warmest time of the year and the months when fishermen are most likely to spot leatherbacks coming up from the South. Leatherback turtles are the giants of the sea turtle world. Up to 2,000lbs, longer than 6ft, and with those shiny parallel ridges running down their blue-black shells, they’re unmistakable. Yet, despite the local consensus that these supposedly tropical turtles roam the waters off Nova Scotia, when biologist Sherman Bleakney proposed in 1965 that these turtles were making an annual northward migration in search of their jellyfish prey, the scientific community dismissed him. After all, sea turtles are warm water animals, incapable of tolerating the harsh conditions of the North. Any turtles sighted North of the Carolinas must be lost, accidental visitors.

Atlantic Canada, feeding grounds for Leatherback Turtles (John Fowler, USGS)

It would be thirty years before scientists would convincingly demonstrate the importance of these northern feeding grounds in the leatherback story. In the 90’s, turtle enthusiast and biologist Mike James decided to follow up on Bleakney’s idea, and came up with a simple test. He distributed hundreds of posters in Nova Scotian fishing communities with a photo of the leatherback turtle and a single emphasized question – “Have you seen this turtle?”

“Yes!” In just one summer, Dr. James received over 170 fishermen-reported sightings of leatherbacks in the waters around Nova Scotia. Since then, Dr. James, staff at the Canadian Sea Turtle Network, and their partners in Trinidad have used satellite tracking, genetics, and turtle-mounted cameras to monitor the migratory and feeding habits of leatherback turtles. All along the way, transporting them to study sites and helping tag the heavy giants, were the fishermen. This inspiring partnership has since been featured in David Suzuki’s “Nature of Things” series, titled Trek of the Titans, available here.

A big reason scientists thought it impossible for sea turtles to spend any amount of time in the cold North Atlantic was because turtles are ectotherms (or cold-blooded), animals with body temperatures comparable to their surrounding environment. Regular body functions (whether it’s a human or a cold-blooded turtle) break down at cold temperatures. Stranded turtles that accidentally end up in the North have been shown to display evidence of cold-shock. Yet, no other reptile exposes itself to the two extremes of the cold Canadian and warm Caribbean waters like the leatherback does.

Leatherback turtle (H. Segars, Nasa.gov)

So how do they do it?

One buffer against the cold is the leatherback’s shear size. Being so large, they have a low surface area to volume ratio. Because there’s very little surface area for heat to escape from, their internal temperature changes very slowly. They’re also have a surprising amount of fat, and can both increase activity and constrict their blood vessels like humans do to keep heat in.

But why bother? What’s so great about Canada anyway?

Jellyfish. Leatherbacks increase their weight by 33% while feeding in Canada, eating more than half their bodyweight in jellyfish. The North Atlantic is full of large nutritious jellies like the Lion’s Mane, which are known to accumulate in high concentrations on the coastal shelves of the North Atlantic in summertime, overlapping with the turtles.

One crucial finding of Dr. James and the Network’s research has to do with the origin of the turtles visiting Canada. Every group of leatherbacks nesting in the Western Atlantic, an area that includes Trinidad and many other small islands, seems to have turtles that migrate yearly to the waters in Atlantic Canada. This means that the Canadian waters aren’t just a vacation spot for a few turtles. Rather, they’re a vital feeding territory for the entire Western Atlantic population.

Lion’s Mane Jellyfish (Tony Hisgett)

Because leatherback sea turtles are as a listed as an Endangered Species in both Canada and the United States, identification of critical habitat is a necessary component of federally mandated conservation efforts. For leatherbacks, these areas seem to include the Southern Gulf of St. Lawrence, the waters off Cape Breton, Southern Newfoundland, and the Northeast Channel boundary area between the United States and Canada.

This is important, because while leatherbacks and other sea turtles are threatened in their breeding ranges by beach development, poaching, and artificial light pollution, they are also threatened in their Northern feeding grounds by entanglement with fishing gear.

That fact makes fishermen even more important partners in leatherback conservation.

Entanglement in fishing gear can compromise a turtle’s ability to swim and even result in drowning. While fishermen have been vigilant about freeing spotted turtles or reporting ones near shore to the Canadian Sea Turtle Network, many turtles die before rescuers can reach them or sometimes afterwards as a result of their injuries. The biggest culprits seem to be bottom and pelagic gillnets, longlines, crab pots, and ghost gear. Fishermen with active lines or nets can rescue turtles, but because leatherbacks feed in areas where jellyfish have aggregated, they spend a lot of time in areas where currents congregate and where lost fishing gear tends to end up.

So what’s next?

Staff at the Canadian Sea Turtle Network and the Canadian government continue to track tagged turtles. It’s not currently known exactly how many turtles make up the Atlantic population, though it’s thought that young survival at breeding areas is improving thanks to innovative conservation partnerships. Following their legacy of researcher-public partnership, the Network partners with Nature Seekers in Trinidad to both monitor nesting beaches and educate people about the turtles, to prevent poaching and other disturbances.

Tagged Leatherback Turtle surfaces while feeding on jellyfish, revealing satellite tag (Canadian Sea Turtle Network)

Staff are also now working with Canadian fishermen to study loggerhead sea turtles, another frequent visitor to the North Atlantic but much more cold susceptible. They’ve discovered that most loggerheads in Canada are juvenile adults from nesting beaches in Florida. They’re also working with fishermen to come up with new ways of removing fishing hooks from loggerheads to improve survival after rescues.

This kind of respect-driven partnership between scientists and the fishing industry may be the key to turning around the problem with marine debris, seen by some researchers as the last front in the fight for sea turtle conservation. With nesting beaches increasingly protected, it’s important we are also protecting feeding grounds. Researchers on the other side of the continent, studying the Pacific leatherback population, suspect that their turtles are faring so much worse than the Atlantic group because they have to travel so much more to find food. Atlantic leatherbacks are literally swimming in jellyfish, but entanglement in fishing gear combined with changes in a climate-dependent food source still pose a risk to ongoing conservation efforts. Working together, we might still have time to save them.

To follow the Canadian Sea Turtle Network and learn how you can help turn the “tide” on marine conservation issues, check out their website or facebook page.

 

 

 

 

 

 

 

 

 

 

Discussion

2 Responses to “Turtles of the North – Canadian Fishermen Help Scientists Study the Cryptic Leatherback”

  1. Is there something about the leatherback cardiovascular system that can maintain a higher core temperature in cold water ?

    Posted by Dick Kenney | August 31, 2018, 9:32 pm
    • R J Parker

      Hi Dick, good question. It seems that the leatherbacks massive size is the main determining factor for keeping warm in cold waters. Having a relatively small surface area compared to high body volume, combined with ample fat stores, means the turtles are predisposed to retaining heat. They also have the ability to restrict blood flow to extremities to avoid losing heat in cold waters, just like we do. To maintain their warm body temperatures, leatherbacks have to create (and save) more heat than they lose to the surrounding ocean. We know that they can do this by increasing activity, such as swimming more in response to cold, but we aren’t sure yet how important muscle-generated heat is compared to heat generated by other organs (like by the stomach when digesting all those tasty jellies!) Thanks for reading!

      Posted by R J Parker | February 18, 2019, 9:39 am

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