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River Otter Control Efforts Gain Traction

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HOUSTON, Mo.-Missouri trappers seem to be getting a handle on river otter numbers in the Ozarks, according to a report from the Missouri Department of Conservation. With a little help from world fur markets and knowledge gained through studies and field experiments, the agency hopes to find an acceptable balance between the needs of river otters, anglers and property owners.

The river otter was all but extirpated from Missouri by the early 20th century as a result of habitat loss and unregulated trapping. In 1982 the Conservation Department launched an otter restoration effort, eventually releasing 825 otters from Louisiana in 34 counties.

To say that the otters thrived is an understatement. Their population growth and spread outstripped all expectations. The sleek predators took advantage of habitat from national wildlife refuges to farm ponds and small streams, quickly populating areas where they were released and spreading across watersheds into new territory.

“Nothing in other states’ experience prepared us for the level of success our otter restoration program had,” said Private Land Field Programs Supervisor Rex Martensen. “We didn’t realize how adaptable they were or how much of the state had suitable habitat for them.”

Missouri’s success at otter restoration had a downside. As otters went in search of food - crayfish in the warm months supplemented with finned fish during the winter - they came into more frequent conflict with people. Some otters cleaned fish out of farm ponds. Others visited headwater streams in the Ozarks, where fish in small pools were easy prey. A few found the ultimate otter buffets - rearing ponds at fish hatcheries.

Faced with too much of a good thing, the Conservation Department set about documenting otter problems. Then the agency turned to the only people with the know-how, the numbers and the incentive to reduce otter numbers - fur trappers.

River otter pelts are among the most luxurious and sought-after in the world. In years when demand is high, exceptional pelts might bring $140. With that kind of reward, trappers were motivated to help reduce their numbers.

To further encourage trappers, and to focus their efforts where they were needed most, the Conservation Department divided the states into five otter trapping zones. It based the length of otter trapping season in each zone on the number of otters and the frequency of otter problems.

The response was encouraging. The otter harvest increased every year from the 1999-2000 season through the 2005-2006 season, peaking at 3,274.

The otter harvest took a significant dive during the 2006-2007 season, plunging from 3,274 to 1,929 (70 percent) in a year. Part of the reason was that the average price that otter pelts commanded fell from $125 to less than $40 during the same period. Weather also was a factor. Extreme cold, ice, snow and rain kept trappers indoors during part of the 2006-2007 season, further depressing harvest.

Nevertheless, Conservation Department resource scientists have found evidence that five years of concerted effort to increase otter trapping is reducing otter numbers in target areas without impairing the population’s ability to sustain itself.

To better understand the effect of trapping on otter populations, the Conservation Department has been conducting a population dynamics study in two areas - north-central Missouri and in the central Ozarks on the Gasconade and Big Piney rivers and the Osage Fork of the Gasconade River.

Conservation Department workers captured and tagged 262 otters with radio transmitters, then kept track of how many died and how. Seventy-nine percent of the otters that died were taken by trappers.

Based on population estimates, biologists calculate that trappers are taking between 16 and 40 percent of the otters annually in the north study area and 30 to 50 percent in the Ozark study area. Otter numbers seem to be declining slowly in some Ozark streams as a result of trapping.

In another experiment, the Conservation Department sought to reduce otter numbers in Roubidoux Creek in Texas and Pulaski counties. Otter numbers declined dramatically in the study area, and fish populations showed a significant increase.

“Fish in small Ozark streams face other problems, such as gravel burying their habitat, low stream flows and pollution,” said Martensen. “Yes, otters do impact fish populations, especially in smaller headwater streams. However, in larger streams with sufficient habitat, otters’ effect seems to be minimal. We still have a lot to learn about how the presence of otters, and other factors, such as gravelling in, water quality and changes in seasonal stream flows, interact to affect fish.”

He said the Conservation Department will continue to work toward management strategies that allow river otters to coexist with people.

“Otters are here to stay,” he said, “but there is no reason we can’t have otters while protecting fishing resources and private property. It’s a matter of finding a balance.”

-Jim Low-


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