The aquatic habits of the otter allow it to exist in several life-zones, in both marine and fresh-water habitats. The principal environment is the streams, rivers and lakes of the Transition Life-zone, but along the larger rivers, otters range up into the Canadian Life-zone and along the Snake and Columbia rivers they enter the Upper Sonoran Life-zone. They are active throughout the year. As we have observed them, they are principally nocturnal.
Otters are extremely powerful swimmers. Tracks along the North Fork of the Tolt River, King County, showed where otters had entered water that flowed over a stony bottom at the velocity of rapids. Their occurrence in the Tolt, Skykomish and Snoqualmie rivers where these are swift mountain streams indicates exceptional swimming ability. After emerging from the water, an otter often follows along the shore, sometimes for miles.
In the San Juan Islands the otters have taken to a marine existence. In the summer of 1938, abundant opportunity offered to observe the otters at Thatcher Bay, Blakely Island. Here, in the evening, bats were shot as they flew over the calm water of the bay. Specimens killed were retrieved by rowing out to them with a dory. For the first two nights bats were collected and retrieved without incident. On the third night, several of the bats vanished between the time they were killed and the time that the boat was launched from the rocky beach. The presence of a shark or other large fish was at first suspected, but observation showed a group of three or possibly four otters to be the thieves. On succeeding nights the animals became bolder. A dead bat became the object of a race between otters and collector. They completely ignored shouts, dodged stones hurled at them, and stole almost all the bats shot. Only a sense of humor and desire to study the animals saved them from a load of fine shot. Bat collecting was given up in disgust.
These otters were remarkably seallike in many actions. In swimming their heads, shoulders and part of their back were exposed. In resting in the water, only the round head remained above the surface. They were never seen to float prone on the surface or rest on their backs, as does the sea otter. They were noisy swimmers, splashing with paws or heads as they dived. Their eyesight was remarkable. Stones the size of a walnut were hurled at them from distances as short as 25 feet. All were dodged with little effort. In this connection the experience of two trappers who caught an otter in the Samamish River near Woodinville, King County, is interesting. The trap holding the otter had been attached by a wire 6 feet long to a pole on the bank. The wire was detached from the pole; while one trapper held the wire, the other tried to strike the otter with an oar as the boat drifted over deep water. The otter was free to swim and dive for the length of the wire and trap chain. It detected, and evaded by dodging or diving, every blow directed at it and not until the animal tired, a half hour later, could it be killed. The trappers then noted that the splashing of oars and otter had nearly filled the boat with water. The trappers were exhausted.
The otters of Blakely Island were not unique in occupying a marine habitat. At Strawberry Bay, Cypress Island, on July 5, 1938, fishermen brought in a "strange animal" caught by them at Black Rock, a tiny bare and isolated islet 5 miles to the west. The heavy box holding the animal was opened, disclosing a very frightened young otter. Questioned, the fishermen stated that four young and one adult had been seen in the surf. They had thought the animals a species of seal, and were somewhat surprised at being successful in their attempts to catch one. The otter was too young to fare for itself and was kept in camp in the hope that it might be reared and released. It ate a few fresh herring and candlefish and drank some condensed milk. It refused whole salmon and sea bass but ate some skinned and boned strips of these fish. It died a week after it was captured. This young otter made a ticking sound, almost a chirp. A variety of crying and whimpering sounds were also made, and when petted it grunted in satisfaction. If surprised or when first picked up it gave a deep harsh growl, unexpectedly vicious in sound, for such a small animal.
The otters at Blakely Island fed on a great variety of food. The only food they were actually seen to eat was candlefish, a slim silvery fish 6 inches in length. On several occasions an otter was seen swimming with the head of a candlefish held fast in its mouth and the fish's body extending out in a silvery bow. Many feces of these otters were composed entirely of the feathers of grebes and scoters. These birds were probably not killed by the otters but died a natural death or were shot by men. At that camp scarcely a day passed in which at least one person was not seen firing a .22 caliber rifle from a cabin cruiser into the flocks of scoters at the mouth of the bay. Dead sea birds were common on the shore and doubtless furnished food for otters as they did for crows and eagles. The majority of the otter feces examined at Blakely Island were composed of the remains of invertebrates. The small mussel (Mytilus edulis) was most abundant. Crabs formed an important part of their diet. Strangely enough the shore crab (Hemigrapsus nudus) and the porcelain crab (Petrolisthes eriomerus) were seldom eaten though they were abundant beneath the rocks upon which the feces were found, and formed the principal food item of raccoons. These species of invertebrates live beneath rocks and the raccoon probably reaches beneath the rocks to catch the crabs with its handlike forefeet, as the otter is unable to do. The edible crab (Cancer productus) and kelp crab (Telmessus cheiragonus) were most often eaten by otters. Also eaten were snails (Margarites, Littorina), bitter oysters (Pododesmus macroschisma), unidentified pelecypods, barnacles (Balanus), one chiton (Mopalia muscosa), and once a starfish. The invertebrate remains, save for the snails, were crushed and broken.
Fish of many species were abundant in these waters. Salmon were often seen leaping near the playing otters. Yet no scales or other remains of fish were detected in the feces. Candlefish possess tiny scales that could probably be seen by microscopic examination only. As for the bird remains, the quantity of feathers consumed is notable. The otters apparently do not pluck birds, as do minks. Indeed, of the material eaten, the food value by volume seems extraordinarily low. A great quantity must be eaten to nourish an animal as large and as active as an otter. The number of fecal droppings seen each morning indicates that this is the case.
