what do they feed on?
They eat aquatic and semiaquatic animals.
North American river otter
A highly active predator, the North American river otter has adapted to hunting in water, and eats aquatic and semiaquatic animals. 
where do river otters go in the winter During winter, the North American river otters heavily use openings in the ice, and may excavate passages in beaver dams for accessing open water. what are these creatures? The North American river otter also known as the northern river otter or common otter, is a semiaquatic mammal endemic to the North American continent found in and along its waterways and coasts. how is their temperament? are active year-round, and are most active at night and during crepuscular hours. They become much more nocturnal in the spring.
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North American river otter [SEP] Hunting
A highly active predator, the North American river otter has adapted to hunting in water, and eats aquatic and semiaquatic animals. The vulnerability and seasonal availability of prey animals mainly governs its food habits and prey choices. This availability is influenced by the following factors: detectability and mobility of the prey, habitat availability for the various prey species, environmental factors, such as water depth and temperature, and seasonal changes in prey supply and distribution in correspondence with otter foraging habitat.