New Jersey is home to aquatic and semi-aquatic mammals


By Michele S. Byers

You’re walking near a stream or a lake and suddenly catch a flash of a small, sleek creature with dark, glossy fur. Could it be a mink?

Or maybe you hear a loud slap on the water, followed by a glimpse of a submerged creature diving under a pile of sticks and logs. Could it be a beaver?

Yes and yes!

Mink and beaver are native New Jersey mammals found in and around freshwater. They and other aquatic and semi-aquatic mammals – including otters, weasels, ermine, fishers and muskrats – are in this state we’re in, but they are not easy to spot.

“They are incredibly secretive,” said Dr. Emile DeVito, staff biologist for the New Jersey Conservation Foundation. “Nobody really studies them in New Jersey. They are an overlooked group of animals, except by trappers.”

Anecdotal evidence suggests these aquatic mammals are becoming more common due to cleaner waters, more forest cover and less trapping. But because these animals are most active at dawn, dusk and nighttime, they are not often seen.

But if you are in the right place at the right time – possibly even in broad daylight – here’s what you might see:

• Mink (Mustela vison) – Known for their exceptionally beautiful and soft fur, American mink have a lanky body, long tail, short legs and partially webbed toes, which make them excellent swimmers.

They are a member of the Mustelidae family, which includes otters, fishers, skunks and weasels. Mink are solitary and territorial, feeding on crayfish, frogs, fish, mice, reptiles, earthworms, and waterfowl.

Like their skunk cousins, mink defend themselves by spraying a foul-smelling liquid.

• Beavers (Castor candensis) – Beaver are among the few animals, other than humans, who completely reshape their environment to suit their needs.

After damming a stream to create a pond, they build a separate beaver lodge. They pile mud, rocks and sticks inside the lodge to form a “floor” above the water.

On top of this, they weave sticks into a large mound. They burrow up through the floor and chew out branches from within to create a “room.”

Beavers live in communal groups and slap their flat tails to warn of danger. Unlike many of the other animals on this list, beavers are not carnivorous  – they are part of a unique family in the rodent family, and are vegetarians whose favorite foods include water lily tubers, spatterdock, clover, algae, apples and the leaves and green bark from trees.

• River otters (Lutra canadensis) – Otters are the most aquatic members of the mustelid family. Their long stiff whiskers help them find prey, and special flaps allow them to close off their nostrils and ears to remain underwater for up to eight minutes on one breath.

They are highly social and form family groups centered on a female and her young. They eat fish, reptiles, amphibians, crustaceans, mollusks, insects and even small birds and mammals.

• Ermine (Mustela erminea) – Ermine is another name for short-tailed weasel. They are famous for snowy white fur, but that’s just their winter coloring.

In the summer, ermine coats are brown with white chests and bellies. Like mink and other weasels, they have long bodies, short legs, round ears, long tails and long whiskers.

New Jersey is also home to long-tailed weasels (Mustela frenata), which do not change color in the winter. Weasels are carnivores like dogs, cats, bears and raccoons.

• Fishers (Martes pennanti) – Fishers are the rarest of New Jersey’s water-loving mammals and are making a comeback in northwestern New Jersey after an absence of 100 years.

These fierce carnivores go after squirrels, rabbits, chipmunks, mice, raccoons, shrews and even porcupines.

According to the Conserve Wildlife Foundation of New Jersey website, “The best description of a fisher would be to imagine a cross between a cat and a fox with the nasty attitude of a wolverine.”

• Muskrats (Ondatra zibethicus) – Despite their name and long, skinny tails, these rodents are not actually rats.

Semi-webbed toes on their hind feet help them swim, and they eat roots, stems, leaves and fruits of aquatic plants, as well as small fish, clams, snails, crayfish and turtles.

Muskrats sometimes build water houses like beavers, but they do not build dams. They have scent glands that secrete a musky odor – hence their name.

Enjoy wildlife watching in New Jersey’s great outdoors and with luck you might spot some of these fascinating aquatic and semi-aquatic mammals.

Michele S. Byers is the executive director of the New Jersey Conservation Foundation, Far Hills. She may be reached at [email protected]