North American river otters

Slater, Emmet, Olive, Olivia, and Emilia

by Dave Gibson

Though no definitive historic population numbers are available, river otters at one time numbered in the hundreds of thousands in the U.S. and Canada. Once one of the staples of the French fur trade, in the year 1800 alone there were 65,000 river otters harvested. By the turn of the nineteenth century, due to unregulated trapping, habitat loss, and pollution, there were estimated to be only 4,500 left in the continental United States. Extirpated from most Eastern and Midwestern states, it is only recently that river otter populations have begun to recover. Particularly sensitive to aquatic contamination, water pollution controls enacted in the 1970s have benefited the otter, as have newly instilled hunting and trapping regulations. Twenty-one states, including a large portion of the Rocky Mountain West, now have active reintroduction programs in place, where over one thousand have been released into the wild. Rocky Mountain National Park, Grand Lake, Boulder Creek, and the Western Slope are some of the places where otters can be found in Colorado. Currently listed as a species of least concern, there are estimated to be 100,000 river otters living in the U.S. today.

River otters inhabit lakes, rivers, swamps, coastal bogs, and estuaries. Their long whiskers, needle-sharp teeth, streamlined body, webbed feet, and claws are an asset while pursuing their usual prey of catfish and suckers. Cooperative group hunting techniques are sometimes employed to herd and acquire faster-moving fish such as trout. Crayfish, mussels, freshwater clams, snails, turtles, frogs, salamanders, snakes, squirrels, birds, mice, and insects supplement the rest of their diet. Otters can grow to be thirty pounds and consume one quarter of their weight each day to maintain their high metabolism. Noted for their playful disposition, they are often observed frolicking in the water or sliding down snow and mud banks.

Zoo and aquarium river otter populations in the United States are self-sustaining and genetically diverse. From time to time, otters are rescued to live out their lives as ambassadors for their species. Such was the case with Slater, who was brought to Denver’s Downtown Aquarium from a failed Louisiana animal rehabilitation center. Slater has been a resident at the aquarium since their inception almost nineteen years ago. Senior citizen Slater is now twenty years old and has lived eleven more years than the average otter in the wild. His time is contently spent eating, napping, and playing with his seven-year-old buddy Emmet, who the aquarium added for company in 2011 from the Binghamton Zoo, NY.

Olive had been raised by someone and imprinted on humans. She was found abandoned, confused, scared, and frantic at a Tampa, FL, gas station a couple of years ago. The Downtown Aquarium was all too happy to give her a forever home along with two other female otters that were rescued a few months later. An Alaskan Aleutian Islands resident trapped and relocated an adult river otter that was attacking his dog, not realizing that the captured otter had a brood of young living under his porch. By the time he discovered the pups they were malnourished and suffering from metabolic bone disease. The resulting deformities to their legs would make it impossible for them to survive anywhere but in captivity, so they were transported to Denver and nursed back to health. Physical therapy sessions – that are more like playtime with fish rewards – continue for Olivia and Emilia three to four times a week. The three females (Olive, Olivia, and Emilia) have formed a strong sisterhood and kept separate from the two males (Slater and Emmet), mimicking their natural behavior. All of the otters seem happy, are meticulously cared for, and have ample space with swimming ponds. They are especially active when receiving two kinds of smelt, rainbow trout, capelin, crabs, clams, mussels, a ground beef mixture, and the otters’ favorite food shrimp during their feeding times throughout the day.

You may visit the otters at the Downtown Aquarium, 700 Water St., Denver, CO, Monday through Thursday 10 a.m. to 9 p.m., Friday and Saturday from 10 a.m. until 9:30 p.m., and Sunday 10 a.m. to 9 p.m. Beyond the price of admission, a special “Meet and Greet” can be arranged to get up close and personal with the well-adjusted friendly river otters. For more information about the Downtown Aquarium go to or call (303) 561-4450.

Dave Gibson has been a contributor at the Weekly Register-Call for over a dozen years. To view past articles and pictures go to

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