Study probes turtles’ survival years after oil spil

Unlike mammals and birds, which normally die after a few weeks, northern map turtles, which can live up to 60 years, can survive after being oiled for months.

Study probes turtles’ survival years after oil spil

Representational Image (iStock)

New research at The University of Toledo indicates that turtles rehabilitated in the wake of the accident had exceptional long-term survival rates, 12 years after an oil spill covered roughly 35 miles of the Kalamazoo River.

Following an Enbridge pipeline burst near Marshall, Michigan, in July 2010, which released 843,000 gallons of oil into a river’s tributary creek, the most significant inland oil spill in American history, turtles were the most often found oiled creatures. Nearly 8% of the northern map turtles that were retrieved from the spill perished right away.

Josh Otten, a biologist who received his Ph.D. from the University of Toledo in May, was one of the first environmental responders on the scene and is the lead author of a recent research that was published in the journal Environmental Pollution.


As a doctoral student in the lab of Dr. Jeanine Refsnider, associate professor in the UToledo Department of Environmental Sciences, Otten assisted in organising efforts to rescue, rehab, and release thousands of injured turtles in 2010 and 2011. She later returned eight to eleven years after the oil spill to evaluate the status of the turtle population.

In the 14 months after the accident, he discovered that the rehabilitation procedure dramatically raised the monthly survival probability of northern map turtles, demonstrating the significance and efficiency of oil removal from turtles.

Additionally, the success is sustained over time. The differences in monthly survival probability between turtles affected by the leak and those who were not had almost vanished 11 years after the disaster.

In order to increase turtles’ chances of surviving after a significant oil spill disaster, Otten emphasised that it is crucial to invest time, money, and effort in their rehabilitation process. “Eight to eleven years after the oil disaster, the northern map turtle population in the Kalamazoo River appears to be healthy and steady.

He said that between 2018 and 2021, a sizable number of adults, youngsters, and hatchlings were collected and recaptured, indicating population expansion. Additionally, there are high monthly survival rates throughout this time.

“Rescuing and rehabilitating individual animals is relatively common practice following an environmental disaster such as an oil spill. It often is a way for volunteers and other local people to feel like they are helping to fix 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 at increasing survival rates of rehabilitated individuals. This is one of the few studies that directly measured both short-term and long-term survival rates of animals after undergoing cleaning and rehabilitation due to a major oil spill.”

To understand how the turtle population is doing today and to identify specific turtles that had been saved and rehabbed during oil spill cleaning activities in 2010, Otten’s Ph.D. research involves comprehensive recapture, radio-telemetry, and nest-monitoring investigations.

The scope of Josh’s investigation, which spanned a 10-year period, was “really unparalleled” according to Refsnider. “He handled many thousand turtles over approximately 50 kilometres of river over the course of this study and accumulated a vast dataset of capture histories and locations for turtles,” he added.

The turtle population study, which was supported by the U.S. Fish and Wildlife Service, concentrated on northern map turtles and calculated monthly survival rates of turtles exposed to the freshwater leak up to 14 months after the spill and again for 8-11 years following the environmental catastrophe.

2,100 northern map turtles affected by the leak were caught in 2010 and 2011, cleaned up, given rehabilitation, marked, and then reintroduced into the Kalamazoo River. 63% of them were only ever taken once.

Otten added, “The likelihood that I would recapture them is quite minimal. Northern map turtles can be challenging to capture to begin with.” Other factors including emigration, translocation, and natural mortality are also taken into account. There are undoubtedly a good number more that have evaded capture throughout the four years I conducted my survey. The recapture rates are very impressive for long-term turtle survey operations and detectability.

Unlike mammals and birds, which normally die after a few weeks, northern map turtles, which can live up to 60 years, can survive after being oiled for months.

According to the study, turtles may have a delayed reaction to an oil spill because they often perished nearly 60 days after being captured during the rehabilitation process while under the care of veterinarians.

This demonstrates the value of ongoing wildlife rescue after a spill, especially if turtles are involved, according to Otten.

Following the Kalamazoo River oil spill, the researchers discovered that northern map turtles that had received any form of rehabilitation had a much greater monthly survival rate than those that had not. Additionally, they discovered that in the 14 months following the spill, overwintering turtles, or those turtles who spent the most time in rehabilitation (from September 2010 to May 2011), had the highest monthly survival rate.

Regarding how the oil in general affected the ecology, Otten noted, “There are so many unknowns.” We don’t know whether there may have been a change in the availability of food, whether oil accumulating in turtles’ wintering grounds affected their ability to survive, or even how cleanup activities like boat traffic and erosion may have impacted turtles.

Due of these factors, it is crucial to carry out studies like this one years after a disaster to spot trends and advise researchers, cleanup teams, and government organisations on how best to allocate their time and resources.