Tales of the North Pacific

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Tales of the North Pacific

The other name for orcas is ‘killer whale.’ Orcas are the most fearsome predator in the sea.

When attacked by orcas, a pod of great whales formed a daisy pattern, head toward the center, tails out. Great whales are several times the size of orcas. The idea was probably to whack the attacking killer whales with their tails; or to limit their access to whale bodies.

Orcas are intelligent, powerful and not easily discouraged. Their dentition resembles that of Tyrannosaurus rex. Wounded great whales would be nudged back into formation by their companions, trailing their intestines or missing great flaps of skin. The whole pod might be killed.

Dead whales sink to the bottom of the ocean, where they become the base of a novel ecosystem including polychaete worms that live on the fat in whalebone. Before industrial whaling, 850,000 whale carcasses may have littered the seafloor at any one time. Besides supporting their own ecosystem, the carcasses contributed nutrients to the deep sea.

Orcas are opportunistic hunters and also eat seals, sea lions and fish, including herring and salmon. They have a high metabolic demand and need a lot of food. Stellar sea lions, which weigh up to a ton, provide a good meal.

During World War II, fishing in the ocean almost stopped. After the war, life returned to normal. The whale hunt in the North Pacific resumed. About 500,000 great whales were killed there.

During the 20 years of the hunt, orcas learned to respond to the sound of exploding harpoons and whale distress calls. Like gulls, they followed cruising ships. Many harpooned whales escape. These were fat years for the killer whales.

When the hunt ended, whales were few. The biomass of fin and sperm whales in the North Pacific had been reduced by 90% or more.


As the hunt wound down in the 1970s, harbor seals began to decline, followed by Stellar sea lions and fur seals. The declines were rapid and surprising. Stellar sea lions are now considered endangered.

Fur seals had been hunted almost to extinction by American and Russian sealers toward the opening of the twentieth century. Their populations had recovered under a treaty that let the Aleut natives of the Pribolov Islands, their breeding grounds, manage them.

The reason for the decline of these marine mammals was unknown. It was first blamed on overfishing, specifically for pollock, which had begun to replace herring (a more oily fish) in the warming Bering Sea. The white flesh of the pollock is used by chains like McDonald’s in its fish sandwiches.

The decline was also thought to be related to the replacement of the (oily) herring by the (less oily) pollock. Oily fish provide more calories, which sea mammals living in cold water need to maintain their layer of insulating fat; and maintain their metabolisms.

Declaring the Stellar’s sea lion endangered brought boatloads of federal funding. When scientists investigated the pollock fishery, it seemed, for the time being, sustainable. There were enough fish for everybody.

Animals known to have been taken by orcas include blue whales (the largest whale), dogs, great white sharks, sea turtles, moose and sea otters. Orcas capture seal pups resting at the edge of the beach, sliding in on a wave to grab them. Great white sharks flee at the sound of orcas.

In the 1990s sea otters started to disappear. By 1998, 90% of the sea otters were gone from a 1000 kilometer stretch of the central Aleutians. Several tens of thousands of otters were gone.

Sea otters are another predatory animal whose munching on herbivores is thought to keep the world green. They live, or once lived, in the kelp forest of the Pacific coast from northern Japan to Baja California.



Sea otters eat animals that live in the kelp. They are fond of abalone and will hunt them until only those hiding in clefts in the rock are left. They pound the abalone off the bottom with stones. This behavior irritates human fishers (sea otters do the same with beds of mussels) but makes room in the ocean for other invertebrates.

Another favorite food is sea urchins. Sea urchins are covered with spines. Sea otters bite into the soft bottom of the large ones and lick out the insides. The fold up the spines of small ones and pop them in their mouths. The favorite food of sea urchins is kelp.

Sea otters have no layer of fat to keep them warm. Their thick coats do that. To maintain their body temperatures in the cold water in which they live they must eat a quarter to a third of their body weight of 30-100 pounds daily. A lot of sea urchins.

When the shipwrecked German naturalist Stellar wintered on Bering Island in 1741 sea otters were abundant and tame. Like the arctic foxes, whose constant scavenging drove the men crazy, they could be killed with clubs.

Since the otters lack blubber, their insulating fur is the densest of any animal and extremely valuable. The men with Stellar sailed away with 1000 skins, abandoning some of his laboriously prepared specimens on the island. The small boat they cobbled together had only so much room.

Undeterred by the remoteness of the Pacific Northwest, Russian hunters were soon slaughtering sea otters for their skins. They enslaved the native Aleuts to help them. In no time, the Russians were joined by the Americans, who hunted further south.

By 1900 otters were gone from most of their former haunts. The Alaskan otters were hunted out by 1800, but recovered by the 1860s, when they were hunted down again. Sea otters were finally protected by the same treaty that protected the fur seals.

Some otters survived and in the 1970s their influence on the health of kelp forests began to be recognized. Alaska is the center of the sea otter population. Where there were sea otters in the Aleutians in the 1970s, there were dense kelp forests and small sea urchins, where there were no otters, the kelp was grazed down to the bottom by herds of enormous urchins.


In the waving strands of kelp live many fish and invertebrates. Following the abundant fish come harbor seals, sea birds and bald eagles, in numbers greater than where the kelp is missing.

Some sea otter reintroduction programs were successful in reestablishing colonies along the Pacific coast south of Alaska. A colony in Big Sur that had escaped the hunters expanded.

Otters didn’t do as well as formerly. Their habitat was degraded by fishing and runoff. They are susceptible to a disease carried by house cats, whose agents are washed with cat feces down storm drains into the sea.

When in the 1990s, the otters along the Aleutians began to disappear, orcas were not one of the usual suspects. Lacking blubber, otters are not a desirable food for orcas. Three or four hungry orcas could have eaten the tens of thousands of vanished otters over 10 years but more likely several pods of orcas were indulging in otters as a side dish to fur seals, Stellar sea lions, fish and the occasional great whale.

The sea otter tale is one of a predator controlling a grazer, even in the simplified invertebrate fauna of the modern kelp forest (simplified by human fishers).

The orcas demonstrate what happens when a main prey animal is removed: the predatory cascade goes awry. The remaining animals in the ocean can’t satisfy the great hunters’ appetites. They will eat everything available and then starve.

Predatory control of grazers is not always perfect. Sea otters reduce populations of some shellfish to where they are not commercially exploitable (but far from extinct). Wolves will reduce failing populations of moose to zero. Insect populations escape from the control of their bird and rodent predators and eat themselves out of house and home, until controlled by the collapse of the vegetation or by microbes (the ultimate predators). The fear of mountain lions keeps remnant populations of bighorn sheep on their Sierra cliffs during the winter (where they fall on icy rocks) rather than face the hungry lions in the lowlands.

But in most of these cases, the ecosystem has been originally messed up by us.