Douglas Warner has mostly fond memories of the weeks he spent living aboard a sailboat, searching for northern map turtles on some of Ontario’s most scenic cottage lakes. It was August of 2022, and Warner and three colleagues anchored their 26-foot vessel in sandy bays, cooked and ate topside, slept in the cabin’s cramped V-berths, and got plenty of quizzical looks and questions from other boaters. “Every day was an adventure,” he says.
The “turtle pirates,” as Warner and his colleagues fondly called their fieldwork roles, were part of a three-year effort to document the abundance of little-known populations of map turtles on lakes Muskoka, Rosseau, and Joseph by Saving Turtles at Risk Today (START). “It was refreshing for us because it didn’t involve slogging through bogs,” says Warner—that’s the usual procedure for studying Blanding’s and spotted turtles, which are listed as threatened and endangered, respectively, in Ontario and make up the majority of START’s focus.
Wild Profile: Meet the Blanding’s turtle
The team of wildlife technicians towed a pair of canoes behind the sailboat, and each day, they would go paddling to collect, measure, mark, and release map turtles, which are listed as a species of special concern in Ontario. Warner remembers the very first one he captured and the macabre undertone it set for the remainder of his time on the project. “It was a large female, about 30 centimetres long and maybe the width of a football, with a scar from a boat propeller on the left side of her carapace,” says Warner. As the survey continued, he adds, “We were hard-pressed to find an adult female without an old propeller injury.”
Female map turtles are double the size—and up to 10 times the mass—of their male counterparts. Unlike males, females often bask gregariously, floating at the surface in deep water areas with just their heads exposed on sunny summer days. This habit, along with their size, makes them especially prone to boat strikes compared to male map turtles and other species.
Inevitably, Warner and his colleagues wondered how many turtles weren’t surviving boat strikes. “We were finding juveniles and subadults without injuries,” he says. “But if so many adults have scars, how many received lethal injuries?”
A turtle’s shell, while extremely strong, is no match for the sharpness of a spinning propeller blade. “A strike on a smaller turtle will most likely be lethal,” says Sue Carstairs, a veterinarian and the founder of the Ontario Turtle Conservation Centre in Peterborough, Ont. She describes the wounds she’s seen as “long, deep cuts into the shell,” adding that “if these cuts are deep enough to go into the body cavity, the turtle will drown as a result.”
During evenings on the sailboat’s deck, Warner and his colleagues “started to imagine there’s got to be a pile of dead turtles on the lake bottom.” But funding for the map turtle project was not renewed in 2023, and START shelved its data, leaving lingering questions about the actual death toll from propeller blades and the hotspots where collisions take place. Though biologists hesitate to use the term “turtle graveyard” to describe the grisly underwater scenes of Warner’s imagination, they are realizing that boat strikes on cottage lakes are compounding well-known impacts of roadkill and habitat loss in the survival of some of the planet’s oldest—and most endangered—species.
“It’s clear that turtles get hit regularly by powerboats and their populations are fragile,” says Grégory Bulté, a biologist at Carleton University in Ottawa. “Cottagers can play a big role here as they have the power to spread information locally and adopt boating behaviours that minimize impacts on wildlife.”
Northern map turtles, named for the swirly, contour line-like patterns adorning their flattened shells, have webbed claws and muscular limbs to navigate open waters, including Georgian Bay, Lake Ontario, and the Ottawa River, where they feed on molluscs. Researchers suspect the species moved into some lakes in Muskoka and eastern Ontario via the Moon River and the Rideau Canal. Like other species of turtles, map turtles take more than a decade to reach sexual maturity. Females deposit clutches of eggs in sandy, inland areas and promptly return to their aquatic habitat, leaving the eggs to incubate in the sun and any hatchlings to fend for themselves. “Turtles have been around for 200 million years,” says Jeff Hathaway, the executive director of Scales Nature Park, a nonprofit nature centre near Orillia, Ont., and a coordinator of the START project. “They’ve evolved so that the adults nearly live forever, the eggs and babies get eaten, and no one cares.” But clearly, the balance of such an ancient life history tips when adult turtles’ death rates spike due to encounters with cars and boats.
New research sheds light on roads and turtle mortality
Bulté has been monitoring map turtles on Lake Opinicon, Ont., since 2003. He has marked more than 1,000 individuals on this narrow, eight-km-long cottage lake that’s part of the Rideau Canal system, just south of Ottawa. “It’s a good spot for research because it’s a small lake, and we can keep track of the turtles relatively easily,” he says. The majority of Lake Opinicon’s map turtles overwinter on the rocky shoals of one island, where they slow their metabolism and rest in less than a metre of water under the ice. Bulté dons a wetsuit shortly after ice-out each spring to catch turtles, which he then measures, weighs, and marks in the laboratory before returning them to the water. Recapturing marked turtles in subsequent years allows Bulté and his colleagues to monitor the lake’s population dynamics.
“Long-term monitoring is the only way to catch early signs of environmental degradation,” says Bulté.
In a 2010 study published in Aquatic Conservation, Bulté reported that seven per cent of the female map turtles that he captured on Lake Opinicon had propeller scars. He has continued to monitor the population over the years, falling in love with the lake and eventually purchasing property and building a cottage in 2019. When he compared the number of map turtles with propeller scars in 2019 with his data from 2010, the rate had increased to 13 per cent of females. Studies elsewhere in Ontario have shown similar trends. In another 2010 study in Thousand Islands National Park on Lake Ontario, Bulté observed that 13 per cent of female map turtles exhibited propeller scars. Meanwhile, a 2014 study on the Trent-Severn Waterway recorded propeller scars in nearly 29 per cent of females and 13 per cent of male map turtles, as well as considerable evidence of boat-related injuries in Blanding’s turtles, along with eastern musk and snapping turtles, two other Ontario species at risk. “I think that mortality from boat strikes may be an underappreciated threat to turtles,” says Jacqueline Litzgus, a biologist at Laurentian University in Sudbury, Ont., and the co-author of the Trent-Severn paper. This is especially concerning “if small-bodied individuals succumb to their injuries such that they are not captured and represented in tallies of injury rates.”
In his 2010 article, Bulté estimated that a 10 per cent boat strike mortality rate is enough to cause the Lake Opinicon population to decline. The takeaway, says Bulté, is “even a low rate of mortality from boats can be too high for the population to sustain.”
“Injured turtles are a visible symptom of waterways turning into raceways,” he says. If turtles are getting injured and killed by speeding, wake-throwing boats, he adds, there’s “good evidence conditions are also bad for loons, shoreline erosion, noise, and chemical pollution. What we’re seeing with turtles shouldn’t be taken in isolation from everything else.”
Cottage Q&A: Protecting turtle nests
Reducing propeller injuries to turtles on cottage lakes comes down to responsible boating. For Bulté, keeping boats “small and slow” is the ultimate solution. But that vision doesn’t match reality in most places. In their Trent-Severn study, Litzgus’s team concluded that “conservation strategies for aquatic turtle assemblages should consider restricting boat access, speed limits, or both, in areas of high-turtle densities.”
However, posting turtle warning signs and speed limits can’t happen without a better sense of key areas of habitat, and that means funding “turtle pirates,” such as Douglas Warner, to gather more data. Before its funding was scrapped, START was planning scuba transects of lake bottoms to get a sense of where exactly deadly boat strikes are occurring on the Muskoka lakes. “Knowing when and where turtles get hit would be useful in making specific recommendations about boat traffic,” says Bulté. “But every water body is different, so findings from one lake may not apply to another one.”
Veterinarian Sue Carstairs treated 2,300 injured turtles last year, the vast majority wounded by vehicles on roadways—and all reported to the Ontario Turtle Conservation Centre by the public. Many also showed gruesome scars from boat strikes. “We have seen a significant increase in the public’s awareness of the plight of wild turtles over the past decade or so,” says Carstairs, whose organization has more than 50 first responders across Ontario trained to respond to calls of injured turtles. “Boaters need to be more careful, especially in nearshore areas where turtles might be basking. You really can’t tell someone how fast to go [without posted speed limits], but you can make them aware of the impacts they might have. Being aware of potential boat strikes is the first step to preventing them.”
Is your shoreline healthy? Read the signs
There are other ways that cottagers can make shoreline areas friendlier for turtles and other species. Removing underwater vegetation, fallen trees, and floating logs is like “tearing up habitat” for painted and map turtles, eastern musk, and snapping turtles, as well as fish and invertebrates critical to the aquatic food web, says Bulté. When in the water, snapping turtles “don’t want trouble and will scoot away as soon as they sense you,” says Carstairs. Using bubblers to prevent ice from forming around docks is particularly problematic if map turtles are overwintering nearby—the ice acts as protection for them from predators, such as otters. Bulté says such an incident left more than 150 map turtles dead in 2022 on Lake Opinicon.
Much like Carstairs, Warner was buoyed by his 2022 interactions with cottagers on Lake Muskoka. “We received a great deal of support and interest for our conservation project,” he says. “Some cottagers asked us why we were harassing the turtles. We told them we were collecting data to help protect them and that changed their opinion—in a good way.”
This article was originally published in the June/July 2025 issue of Cottage Life.
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