An older juvenile northern map turtle rests on a log. Image: James Harding
By Reese Carlson
The turtles had a long journey ahead.
They fought for 45 miles against the strong Kalamazoo River current. They left the river and walked up and over a dam blocking their path. They traversed water so shallow their shells likely stuck out of it. The destination? Their home 10 years earlier when the 2010 Kalamazoo River oil spill wiped it out.
In July 2010, one of the largest U.S. inland oil spills struck Michigan’s Kalamazoo River. The U.S. Environmental Protection Agency estimated the spill was upwards of 4.5 million gallons.
As part of a wildlife rescue, the Michigan Department of Natural Resources and the U.S. Fish and Wildlife Services relocated more than 700 northern map turtles to similar habitats along the Kalamazoo River.
In the 10 years following the spill, researchers led by Joshua Otten, a research ecologist with the University of Toledo, studied the movements of the map turtles after being relocated. A recent study published in the journal Conservation Science and Practice details the initial emergency move and the turtles’ subsequent movements for 10 years.
“The oil spill was a tragedy. But scientifically? It was an incredible opportunity to learn exactly how far these turtles will go,” said Stephen Hamilton, an aquatic ecosystem ecologist and biogeochemist with Michigan State University’s Kellogg Biological Station. “We had no idea how far freshwater turtles could travel.”
The turtles used their homing instincts to find their way back to their nests. Otten and his team expected this possibility. What they did not expect was the turtles traveling almost 45 miles upstream.
“They will usually move a few miles from their home base, we knew that,” Otten said. “We didn’t have data to support movement at larger distances. We had moved them 30 or 40 miles away from where they had been captured and we found them at nearly the same log they had been captured at originally, 10 years prior.”
The map turtles had made it their personal mission to find their way back. It just took them 10 years to do it.
“Turtles have this homing ability which is really interesting,” said James Harding, a longtime Michigan turtle researcher. “I suspect that odor plays a part in it, but who knows. They could be reading the stars as a guide. Turtles just have this ability that lets them find their way back home.”
This study did more than just share turtle relocation statistics. It also shows that moving them can be successful.
Otten’s study explains that translocated reptiles experience higher death rates when they are moved. It examines the components that made the relocation successful and can be used as a guide for moving reptiles during similar events, Otten said.
“The main issue with the translocation success stories is that they are often just completed translocations,” Otten said. “There are never these follow up studies to see if they survived, so we don’t actually know if some of them are truly successful. They might just appear successful because the animals were released into the wild again.”
Translocation events are tricky, especially with turtles and their homing instincts. They’ll attempt to find their way home and often wander into roads. Just because the animals are back in their habitat doesn’t mean the move is truly successful, Harding said.
The northern map turtle’s success and survival in the Kalamazoo River paves the way for more attempts of this nature. Now that there is data to back it up, regulations and guidelines can be made species specific in the case of another environmental disaster, Otten said.