Twelve years after an oil spill covered nearly 35 miles of the Kalamazoo River, new research at the University of Toledo confirms that turtles rehabilitated following the disaster had high long-term survival rates.
Turtles were the most commonly caught oiled animals following an Enbridge oil pipeline rupture near Marshall, Michigan in July 2010 that spilled 843,000 gallons of oil into a tributary of the river, the one of the largest inland oil spills in US history.
Immediately after the spill, nearly 8% of recovered map turtles died.
One of the first environmental responders on the scene was biologist Josh Otten, lead author of the new study published in the journal Environmental pollutionwho graduated in May from UToledo with a Ph.D. in biology.
Otten helped lead efforts to rescue, rehabilitate and release thousands of turtles affected in 2010 and 2011, returning eight to 11 years after the oil spill to assess the status of the turtle population as a student at the PhD in the laboratory of Dr. Jeanine Refsnider, associate professor in the Department of Environmental Sciences at UToledo.
He found that the remediation process significantly increased the monthly survival probability of northern map turtles within 14 months of the spill, showing the importance and effectiveness of removing oil from turtles.
And the success is maintained over the long term. Until 11 years after the spill, differences in monthly survival probability between spill-affected and unspilled turtles had become almost imperceptible.
“The time, effort and money spent in the turtle rehabilitation process is important to increasing their survival after a major oil spill,” Otten said. “The Northern Map Turtle population of the Kalamazoo River appears to be healthy and stable 8 to 11 years after the oil spill.”
He said large numbers of adults, juveniles and hatchlings were captured and recaptured between 2018 and 2021, suggesting population growth. In addition, monthly survival rates during this period are high.
“Rescuing and rehabilitating individual animals is a relatively common practice in the wake of an environmental disaster such as an oil spill. It’s often a way for volunteers and other locals to feel like they’re helping solve the problem,” Refsnider said. “However, animal rehabilitation efforts can be incredibly expensive and labor-intensive, and very few studies assess whether they are actually successful in increasing survival rates for rehabilitated individuals. “one of the few studies that directly measures short-term and long-term survival rates of animals after undergoing cleanup and rehabilitation due to a large oil spill.”
Otten’s Ph.D. research involved extensive recapture, radio telemetry and nest monitoring efforts to understand how the turtle population is doing today and to identify individual turtles that had been rescued and rehabilitated during the oil spill cleanup operations in 2010.
“The scale of Josh’s study is truly unprecedented – he handled several thousand turtles over nearly 50 kilometers of river during this study and amassed an enormous data set of capture histories and locations. turtles over a 10-year period,” Refsnider said. .
Funded by the US Fish and Wildlife Service, the turtle population study focused on northern map turtles and estimated monthly survival rates of turtles exposed to the freshwater spill up to 14 months after the spill and then again for 8 to 11 years after the environmental disaster.
In 2010 and 2011, 2,100 spill-affected northern map turtles were captured, cleaned, rehabilitated, tagged, and released into the Kalamazoo River.
Of these, 63% were captured only once.
“Northern map turtles can be difficult to capture initially, so the chances of me recapturing them are pretty low,” Otten said. “There are also other things like natural mortality, translocation and emigration that you take into account. I would guarantee that there are quite a few more that have eluded capture over the past four years I’ve studied. In terms of long-term turtle survey projects and detectability, the recapture rates are quite impressive.”
Northern map turtles, which can live up to 60 years, can survive for months after being oiled, unlike mammals and birds which usually die after a few weeks.
The study found that turtles that died during the rehabilitation process while in the care of veterinarians did so an average of nearly 60 days after capture, revealing there may be a delayed response in turtles following an oil spill.
“This shows the importance of continued wildlife rescue after a spill, especially in the case of turtles,” Otten said.
The researchers found that northern map turtles that had undergone rehabilitation following the Kalamazoo River oil spill had a significantly higher monthly survival rate than turtles that had not. They also found that overwintering turtles, or those that spent the longest time in rehab – from September 2010 to May 2011 – while river cleanup work continued, had the highest monthly survival rate. high in the 14 months following the spill.
“There are so many unknowns about the impact of oil on the environment as a whole,” Otten said. “We don’t know if there has been a change in food resources, if the pooling of oil in turtle hibernacula has impacted their survival through the winter, or even how efforts clean-up, including boat traffic and erosion, may have impacted turtles.Because of these variables it is important to conduct a study such as this, years after a disaster, to identify trends and help inform searchers, cleanup crews, and agencies on how best to use time and resources.”
