Nature’s Notebook
Florida’s River Otters
The river otter (Lontra canadensis) is a member of the weasel family, Mustelidae, in the order Carnivora. This semi-aquatic mammal is 3 to 4 feet long, including its tail, and weighs 11 to 30 pounds. The female is smaller than the male. The river otter has black to brown fur, with a lighter brown on its face and belly. It has short legs with webbed feet with five toes. Its body is long and narrow with a flattened head. Its strong tail is one-third the length of the body.
Because of these body features, the river otter is an excellent swimmer and thrives in wetlands, ponds, lakes, streams, canals and estuaries. It can stay under water for four to eight minutes chasing its prey, which includes crayfish, snakes, turtles, crabs, small alligators, birds and fish. The river otter is even known to prey on rabbits and muskrats. Its long whiskers help detect prey in dark and murky water. Its long nails help them hold slippery prey, and its sharp teeth help catch and chew prey.
The river otter has a large home range. The female’s range is 12 square miles when accompanied by young for approximately a year, then increases to 30 square miles without young. The male home range is 60 square miles. The female home range is located in the best feeding areas and does not overlap with other females. The male home range does not overlap with other males, but does overlap with several females. The only time the male spends time with the female is during the fall and winter mating season in Florida when the female is in estrus.
Otter mating season runs approximately from November through April. Estrus lasts only six weeks with receptivity to the male occurring about every six days. The female releases estrus scents at prominent points such as otter latrines (scent posts), dens or rolling places. There can be as many as 40 scent posts within a half mile of suitable habitat. The female otter has a delayed implantation where the fertilized egg cell
does not develop until implanted in the wall of the uterus nine or 10 months later. Gestation takes approximately seven weeks. Young cubs are born in a den with two to four per litter. The female has one litter per year or every other year.
The river otter does not excavate its own den. Otter dens are selected in natural cavities along a ditch, creek, wetland bank, hollow stump or log. I have found otter dens in large pipes along drainage canals. Dens are one to two feet above water.
At birth the cubs are fully furred but their eyes are closed and they have no teeth. After five weeks they open their eyes and play with each other. The cubs are not seen outside the den for 10 to 12 weeks. They are given solid food at this time and are weaned several weeks later. They have to be taught how to swim as they have a difficult time keeping their head above water. A male is not allowed to come near the cubs until they are 6 months old. A male is sexually mature at 2 years, but is not usually successful until 6 or 7 years old.
Because of their large home territories, river otters travel long distances over both land and water, crossing many roadways, which results in many road kills. The otter is most vulnerable to predation when on land as it is very clumsy out of water. Although it can run up to 15 mph, it is easily caught by coyotes, bear and bobcats. It can live up to eight or nine years in the wild or 20 years in captivity.
The greatest chance of observing an otter is from dawn to midmorning and near sunset. It spends the majority of the day grooming and sleeping. It can be observed throughout Florida, with the exception of the Keys. I have observed river otters in Southwest Florida along freshwater wetlands, lakes, ponds, streams and especially canals and ditches. During drier times of the year otters can be seen at Six Mile Cypress Slough. I have also seen them in saltwater environments on Sanibel and Captiva islands. I have observed river otters taking bait out of live wells of fishing boats at Barnacle’s Island Resort (formerly Barnacle Phil’s) on North Captiva and the Green Flash Waterfront Restaurant on Captiva Island and in Braynerd Bayou near the northwest tip of Buck Key.
THE RIVER OTTER IS AN EXCELLENT SWIMMER AND THRIVES IN WETLANDS, PONDS, LAKES, STREAMS, CANALS AND ESTUARIES.