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Identifying Otters

One afternoon in the fall, two otters trapped me. I can't say that I tracked myself into that predicament because in the fall sometimes all I have to do is go to the right spot and wait for the otters to show up. Anyway, I watched them fishing in the pond and then I thought they went into a nearby lodge. I noticed that one of the otters left a bullhead fish on the bank across the pond where they often roll around and poop. So I walked around to see what shape the fish was in.

Then as I was kneeling down studying that, I saw the two otters heading right for me, no doubt, to get that fish. Of course, they saw me, dove and swam off under water.

In the Middle Ages otters were sometimes categorized as fish, and I can understand a Medieval scholar saying to himself, "here's a four legged critter who likes to eat fish, but unlike a cat, raccoon or bear, it actually swims after the fish! Big fish swim after little fish and eat them, so... an otter is best described as a fish!" And there's something to be said for calling an otter a fish. You almost always find them in or right near water. They almost always disappear into the water, sometimes they fly out of it, just like a fish,

and sometimes they do a series of dives just like a porpoise. The German word for otter is "fischotter" which is a much more sensible name than "river otter." You can find many an otter not in a river. I usually see them in small ponds, and they are found fishing well out in the ocean. But it is a rare otter that is not trying to find fish to eat or trying to eat what big fish eat like crayfish and frogs.

Of course, there are other mammals swimming in ponds and rivers. Of them only the mink rivals the otter in eating fish.

But minks are half the size of an otter or less. Their average length is 535 mm, about 21 inches, while the average length for an otter is 1100 mm, about 43 inches, and minks have rather small heads

and they are prone to stay on shore when they see you, while an otter almost always goes into the water and turns into a fish. Minks also have a bushy tail when its dry

and the otter's tail is never bushy. Minks also generally take their catch back to their den, which is what the mink pictured above with the fish did, scurrying along the shore to a dam 50 yards away. An otter usually gets right to work eating a fish, or chomps its tail off so it can't swim away, goes off to get other fish then swims back to eat it. I have a web page about minks.

The other two mammals commonly mistaken for otters are primarily vegetarians.

In this web page, which I'd like school kids to see, I call the dam-building animal pictured above a castor. Indeed its scientific name is Castor canadensis - that last word is Latin for canadian. On average the castor and otter are about the same length, but on average the castor is many pounds heavier: 30 to 70 pounds for adult castors and 12 to 20 pounds for the adult otter. In the photos below the otter looks heavier but that's because it swims more out of the water, because it is lighter!

But its hard for the castor to hide its big triangle shaped head, bigger ears, and notice that paddle shaped tail, quite unlike an otter's tail shown close-up below.

Over the years I've often initially mistaken castors, especially when they are diving for roots at the bottom of a pond, for otters. The photo shows the base of a diving castor's tail.

But in a few moments I can see the castor's big head and ears and notice how slow it is. On rare occasions an otter will lollygag out in the water floating like a log which is what castors often do. And castors can surprise you with their agility in the water, especially if you scare them at the edge of the pond. I did that to a yearling castor and it swam so fast underwater that it made an impressive wave and wake in the shallow pond.

When a castor tires of your presence, it often makes a big splash with its tail to try to persuade you to leave it alone.

Otters have a different styles. Remember those otters that swam back to get the tailless bullhead that I was so rudely standing over? Their heads soon popped up and they gruffly snorted at me, a noise they make by blowing air through loose lips. Otters don't chatter as much as they do in the sound tracks of the nature films like "Yellowstone Otters." Remember, almost all sound tracks are spliced in later and juiced up to add to the visual excitement. I can watch a group of four otters fishing in a pond for an hour and never hear any noise save the occasional splashing of water.

And then there are muskrats, which I have most often thought I was seeing when I was really seeing a small otter. They are rodents like castors though much smaller, half the length of an otter and a fourth of the weight. They can vary their diet but feast on grasses mostly and they are usually seen carrying grass across a pond.

and otters do that rarely, only when they are trying to make a comfortable bed. Muskrat tails are often mistaken for otter tails. The tail is thinner

But muskrats often hold their tails out of the water which otters also do when they are diving for fish. The photo on the left is a muskrat; the one on the right is an otter

However, a few times I've looked at the video I took of what I thought was a muskrat only to see that I actually saw an otter. Unlike the castor, both the otter and muskrat propel themselves with their tail. So when a small otter is simply swimming through a pond without diving for fish, you might see the tail swishing a little behind it and think it is a muskrat.

Of course, that's an otter on the right. Its wake is always bigger and an otter is faster, though a muskrat can sometime rotate its tail fast enough to make like a jet ski! (See my web page on muskrats.) Finally both otters and muskrats have the habit of climbing up on logs floating in a pond.

The animal on the right has much longer body and of course that is the otter.

Another animal mistaken for an otter is the fisher. It is about the same size but despite its name a fisher doesn't swim in the water. I rarely see them so can't give you any pointers save to say they seem much more agile on land than an otter, and they say they can climb trees.

Finally, I'll offer the most important tip for identification. Of all the diving animals, including ducks like mergansers, otters make the most dynamic ripples in a pond when they are diving for fish. A number of otters can bring a pond surface to a boil with ripples.

So when you approach a pond and see the ripples from a dive or splash wait a few seconds. If you see another, and another, and they seem to move every few seconds, then get down and get the binoculars out and look for an animal coming head out with a fish in its mouth or waving a pointed tail high in the air when it dives, and hope you've been trapped by an otter. Enjoy the show.

by Bob Arnebeck

If you have high speed internet here are some videos I put on Google Video that you might enjoy, and you can see a lot more about otters on my Otter Video Book. Here is a short video that shows an otter briefly, then a muskrat, a beaver and then three otters:

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