Window on Nature
By Lowell & Kaye Christie, F47246
River otters belong to the same family, Mustelidae, as badgers, weasels, mink, and until recently, skunks, plus several other species that inhabit North America. Other members of the family can be found everywhere but Antarctica and Australia. Fossil records indicate that otters have been around since the Pleistocene period, several million years ago.
Before Europeans came to North America, river otters lived there comfortably “” from the icy reaches of Alaska all the way to the Gulf of Mexico. They made their living in and around streams, rivers, lakes, estuaries, and salt-water and freshwater marshes.
American Indians harvested otters for food and furs, but not in large enough numbers to cause a scarcity. The decline in the otter population coincided with the arrival of European immigrants. Otter furs were increasingly fashionable, and market hunters were no more concerned about the excessive killing of otters than they were about wiping out bison. But early trappers weren’t entirely responsible for the decrease in otter populations.
These semiaquatic creatures are extremely sensitive to changes in habitat. Man-made dams disturbed watercourses where river otters fished. And pollution that killed fish reduced the food sources available to otters. River otters also are extremely shy and don’t like having humans around. (That’s why most people will only see river otters in a zoo or living museum.) Were it not for the efforts of dedicated conservationists to restore their habitats and reintroduce river otters from remnant populations, these creatures would probably have gone the way of the passenger pigeon. Otter populations have been reestablished to the point where several states and Canadian provinces once again permit limited trapping.
Anglers grumble that otters eat all “their” fish. But this is not true. Admittedly, river otters prefer eating fish as long as they are plentiful. But they also dine on freshwater mussels, frogs, turtles, water birds, and a variety of invertebrates. Several studies also indicate that otters take the mostly slower-swimming rough fish species, and those that are most abundant. These are often species that anglers don’t want, because they offer little challenge or palatable taste.
River otters are excellent fishers. Otters are well adapted for speed swimming, with long, tapered bodies covered with sleek, dense fur. They come equipped with webbed back feet like those of beavers. They can catch a fish faster than a human can drop a line.
And no matter how it looks when you see an otter racing through the water, these animals aren’t all tail: it accounts for only 40 percent of an otter’s total body length. A river otter’s tail is designed for speed “” flat on the bottom to provide plenty of push, and heavily muscled at the base.
A river otter has several more design features worth mentioning. Otter whiskers aren’t just for show; their sensitivity to movement helps them locate fish in the water. An otter’s eyes are near the top of its skull, so it can see what’s going on at the surface even as it cruises through the water.
One might assume that river otters hibernate during the winter, at least in the colder climates of northern Canada and Alaska, but these animals actually seem to enjoy the cold. Well-known for their playful behavior, they are especially entertaining when frolicking in the ice and snow. Thanks to a coarse outer coat of guard hair covering a very dense undercoat, they’re also virtually waterproof. Beneath the otter’s skin is a layer of fat that helps to insulate it from the cold and damp.
You would think that swimming with a thick fur coat would cramp otter’s style. Apparently not, since these critters dive to depths of 60 feet, are able to stay submerged for 4 minutes, and can swim 6 miles per hour. Wish we could do that!
River otters are most active between sunset and dawn. Daytimes are mostly for sleeping. When they’re awake, otters have been described as incredibly playful and endlessly active. Their streamlined bodies serve them as well on land as in the water, as they toboggan across the snow or imitate children on a waterslide. Like children, otters double their fun by dunking each other, doing belly flops or somersaults, or playing otter tag.
A river otter’s life isn’t all play “” they do pause long enough for procreation and pup rearing. Both males and females reach sexual maturity at approximately 2 years of age, but females usually don’t breed until their third year. Predicting a male’s first adventure into fatherhood is less reliable. Where competition is fierce, males often must wait a few more years before a fussy female gives them the nod.
The timing of breeding season varies according to the climate. The breeding gound also varies “” it might be in the water or on dry land. Like several other members in the Mustelidae family, otters use delayed implantation. After conception, the fertilized egg floats dormant in the female’s uterus for up to nine months before implantation in the uterine wall. Another two months pass before the pups are born. Usually, two or three pups are born in a litter.
Young otters are blind and helpless at birth. Their eyes won’t open for another three to five weeks, and they are dependent upon their mother’s milk. As they mature, they begin testing the world outside their den.
Male otters don’t participate in pup rearing, so females are responsible for feeding and schooling their young. Otter pups aren’t born with a desire to swim; their mothers must coax or drag them into the water and teach them how. Fortunately for the youngsters, their mothers keep nursing for another two or three months, until they are able to eat other food.
The pups may enjoy eating the aquatic morsels served up by their parent, but learning to forage for their own food takes time. As they grow more comfortable in the water, their mother demonstrates the art of catching prey. Then, she releases the catch so the young can practice capturing it themselves.
The youngsters will be five or six months old before they can meet their own food needs, but that doesn’t trigger a split between the mother and her offspring. The family usually stays together until a new litter arrives. They’ll continue to share the family burrow on the riverbank or under the roots of a tree. The young may learn to dig their own burrow, or see how to remodel an abandoned beaver lodge. Then they head out into the world.