U.P. otters doing OK
LANSING – The river otter: a sleek swimmer, audience-magnets at zoos and aquariums, whiskered diver, aquatic frolicker, correct answer to crossword puzzle clue for “playful mammal.”
And biomonitor to track toxics that damage the health of an environment or ecosystem.
North American river otters, common in northern Michigan, play that role as “apex consumers” in the aquatic ecosystem – at the top of the food chain. They eat primarily aquatic animals such as fish, turtles, amphibians and crayfish.
“Thus otters serve as biomonitors – organisms that contain information on the quantitative and qualitative aspects of the environment – of wildlife exposure,” according to a new study of toxic chemicals found in Illinois otters.
The study said they’re also biomonitors for human health because the same toxic chemicals found in otters have been found in people who eat contaminated fish.
No such otter study has been done in Michigan.
Doug Reeves, assistant chief of the Wildlife Division at the Department of Natural Resources, said the DNR isn’t worried about overall threats to otter health and survival in the state, although “there are specific watersheds that are areas of concern, not only for otters, for any of the wildlife species that are living in those places, especially those at the top of the food chain.”
Otters have never been designated an endangered species in Michigan, as they had been in Illinois.
In fact, “their numbers have been increasing over the past several years,” Reeves said. “Otters are most abundant in the Upper Peninsula and quite common in the northern Lower Peninsula and in many watersheds in the southern Lower Peninsula.”
The current trapping season ends April 13 in the U.P. and northern Lower Peninsula and March 31 in the southern Lower Peninsula. In the 2011-12 season, 1,018 otters were reported trapped, according to DNR.
The most troubling aspect of the Illinois study, according to lead author Samantha Carpenter, were the highest concentrations of dieldrin ever reported in otters anywhere in the United States. She is a wildlife technical assistant at the University of Illinois, Urbana-Champaign.
Dieldrin is one of the organochlorine insecticides banned in 1978. More than three decades later, high levels of the chemicals remain in river sediments and accumulate in the fish that otters and people may eat.
From 1953 until 1978, dieldrin was widely used on cornfields. Illinois grows more corn than any other state except Iowa. Michigan is also in the top 12, according to the U.S. Department of Agriculture.
U.S. Geological Survey data shows the pesticide was used heavily in much of the Midwest, including the southern part of the Lower Peninsula and areas of the northwest Lower Peninsula.
It’s been linked to neurological, behavioral and immune-suppression problems in wildlife, Carpenter said. Scientific studies disagree on adverse human effects, but some studies have linked dieldrin to asthma, Parkinson’s disease, Alzheimer’s disease and breast cancer.
While the Illinois study didn’t directly test concentrations in fish or sediments, the levels detected in the otters “are indicative of the levels in sediments and fish,” she said.
Researchers based their findings on necropsies – animal autopsies – of 23 otters found by the state wildlife agency from 2009 to 2011. The animals died accidentally, usually by being caught in traps intended for other animals such as beavers.
The University of Illinois conducted the necropsies. Michigan State University’s Diagnostic Center for Population and Animal Health analyzed the liver samples.
Carpenter said, “One of our take-home messages for fish-eating animals is that exposure to the banned pesticide dieldrin may be greater in streams and rivers of the Midwest than elsewhere, given that it was used very intensively in the Corn Belt.”
More study is needed, she said. “We need to understand more about which watersheds are more heavily contaminated than others.”