Giant Pacific Octopus (Enteroctopus dofleini): Size and Facts

What does a giant Pacific octopus look like?

A giant Pacific octopus has a large, baglike body called the mantle, which holds the gills, three hearts, digestive organs and ink sac. In front of it sits the head with two prominent eyes, and from the head spread eight long, muscular arms joined at their base by a web of skin. Each arm carries two rows of suckers, up to about 280 per arm and more than 2,000 in all. The biggest suckers are about 6 cm (2.5 in) across, and every sucker is packed with chemical receptors, so the octopus tastes whatever it touches.

Its usual color is reddish brown, but like other octopuses it can change color and pattern in a moment, turning pale, mottled or dark red. The skin has loose, wrinkled folds along the body and small flaps called papillae, which the octopus can raise so that it looks like a weedy rock. Males can be recognized by the tip of the third right arm, called the hectocotylus, which lacks suckers and is used in mating.

The animal has no bones at all. Its only hard parts are a parrot-like beak made of chitin and the radula, a tongue-like ribbon of tiny teeth. Because the beak is the only part that cannot squeeze, an octopus weighing many kilograms can pass through a gap about 5 cm (2 in) wide. Like its smaller relative the common octopus, it has copper-based blood that turns blue when it carries oxygen.

How big is the giant Pacific octopus?

The giant Pacific octopus is the heaviest octopus that has been reliably weighed, though its maximum size has often been exaggerated.

Much larger figures appear in many books, such as 272 kg (600 lb) and an arm span of 9.8 m (32 ft). They come from a commercial diver’s report in the 1950s and were never weighed or measured by scientists. Very few animals over 50 kg (110 lb) have been reported in recent decades. The full story of record claims, growth and rivals such as the seven-arm octopus is in how big is a giant Pacific octopus?

Habitat and range

The giant Pacific octopus lives along the coasts of the North Pacific Ocean. In North America it ranges from southern California, and possibly northern Baja California, north along Oregon, Washington and British Columbia to Alaska and the Aleutian Islands. On the Asian side it lives off Russia’s Kamchatka Peninsula and in the Sea of Okhotsk, around northern Japan and the Korean Peninsula, and south into the Yellow Sea.

It is a cold-water animal, most common where the water stays around 7–12 °C (45–54 °F). Its copper-based blood carries oxygen less efficiently than the iron-based blood of fish, so it favors cool, well-oxygenated water. Most giant Pacific octopuses live from the intertidal zone down to about 100 m (330 ft), but the species has been recorded at least 1,500 m (4,900 ft) deep.

Good habitat combines hiding places with food. The octopus prefers rocky reefs, boulder fields and kelp forests next to sand, gravel or mud, where it can dig a den under a rock and find buried clams. Divers regularly meet it in Puget Sound in Washington and around Vancouver Island in British Columbia.

What do giant Pacific octopuses eat?

The giant Pacific octopus is a carnivore and a generalist hunter. Crabs and clams usually make up most of its diet, along with scallops, cockles, abalone, snails, shrimp, fish, squid and other octopuses. It has also been seen catching spiny dogfish, a small shark, in an aquarium, and dogfish remains have been found outside wild dens. In 2012 a photographer recorded a wild giant Pacific octopus seizing and drowning a gull.

It finds prey by sight and especially by touch, probing crevices with its arm tips or pouncing to trap an animal under its web. To open a clam it can pull the shell halves apart, crack the shell with its beak, or drill a small hole using its radula and a toothed organ called the salivary papilla. It then injects saliva that paralyzes the prey and loosens the flesh.

Most meals are carried home and eaten in the den, and the empty shells pile up outside as a midden. More detail on prey, hunting and shell drilling is in what do giant Pacific octopuses eat?

Dens and daily life

Giant Pacific octopuses live alone. Each one uses a den: a crack in the rock, a hole it has dug under a boulder, or even human trash such as a tire, pipe or barrel on the seabed. The den is usually just large enough for the octopus to fit inside and turn around. An octopus may use the same den for a month or longer before moving to a new one nearby.

Tracking studies have found that these octopuses spend more than 90 percent of their time resting or hiding in a den, among kelp or camouflaged on the bottom. They can be active at any hour but forage most at night. To travel on the seabed they crawl on their arms; to escape they shoot backward by jet propulsion, forcing water out through the funnel, and may release a cloud of dark ink.

How smart is the giant Pacific octopus?

Octopuses are generally considered the most intelligent invertebrates, and the giant Pacific octopus is the species most people meet in aquariums. Captive animals learn to unscrew jar lids, take apart objects in their tanks and, occasionally, escape through gaps in the lid. Keepers describe clear differences in temperament between individuals, from bold and playful to shy.

Some of their abilities have been tested. In a study at the Seattle Aquarium published in 2010, giant Pacific octopuses learned to tell apart two people wearing identical uniforms: one who always fed them and one who always touched them with a bristly stick. By the end of the experiment, most of the octopuses reacted differently to the two people, for example by approaching one and aiming jets of water at the other. For problem solving, learning and play across octopus species, see how smart are octopuses?

Reproduction and the mother’s last months

Giant Pacific octopuses breed only once, near the end of their lives. During mating, which can last hours, the male uses his hectocotylus to place sperm packets called spermatophores, each up to about 1 m (3.3 ft) long, inside the female’s mantle. The female can store the sperm for months; one female at the Seattle Aquarium kept it for seven months before laying fertilized eggs.

She then seals herself into a den and lays tens of thousands of eggs, with published estimates ranging from about 20,000 to 100,000 or more. Each egg is about the size of a grain of rice, and she hangs them in strands and clusters from the roof of the den. For the next five to seven months, and longer in very cold water, she blows fresh water over the eggs, cleans them with her arm tips and drives away egg thieves. She does not leave to hunt, so she slowly starves and usually dies around the time the eggs hatch.

The hatchlings drift in the plankton for one to three months before settling on the seabed. Very few survive, but those that do grow remarkably fast, by close to 1 percent of their body weight every day.

How long do giant Pacific octopuses live?

Giant Pacific octopuses live about three to five years, both in the wild and in aquariums. That is long for an octopus, since many species live only one or two years. Their lives are cut short by breeding. After mating, males stop eating and decline within a few months, and females die after their long brood. This programmed decline, called senescence, brings loss of appetite, white sores on the skin and aimless wandering, and it is controlled by the optic glands near the brain. Experiments suggest that warmer water speeds up growth and breeding and can shorten the octopus’s life. The same pattern across octopus species is explained in how long do octopuses live?

Predators and threats

Eggs left unguarded are eaten by fish and other scavengers, and the drifting young are eaten by many plankton feeders. Adults have fewer enemies, but harbor seals, sea otters, Pacific sleeper sharks and sperm whales all eat giant Pacific octopuses. People catch them too, especially in northern Japan, and in smaller numbers off Alaska and Canada, often as bycatch in crab and cod pots.

Environmental changes may matter more in the long run. In Washington’s Hood Canal, seasonal low-oxygen dead zones force octopuses into shallower water, while brooding females cannot leave their eggs. Ocean acidification may reduce the crabs, clams and other shelled animals they eat, and researchers have found high levels of heavy metals and PCBs in the digestive glands of some wild octopuses, probably taken in with their prey.

Conservation status

The IUCN Red List classifies the giant Pacific octopus as Least Concern, in an assessment published in 2018. It is widespread, breeds in large numbers and grows fast. Its populations are still hard to count, because the animals are solitary and hidden, and genetic studies suggest that octopuses in Japan, Alaska and Puget Sound may be distinct populations.

In Puget Sound, the legal taking of a giant Pacific octopus at a popular Seattle dive site in 2012 caused a public outcry. Washington’s Fish and Wildlife Commission responded by protecting giant Pacific octopuses at seven popular dive sites in the sound.

Giant Pacific octopus and people

Few invertebrates are as popular. The giant Pacific octopus is a star attraction at aquariums across North America, Europe and Asia, where keepers give it puzzle feeders and toys to keep it busy. In the wild, divers in British Columbia, Washington and Alaska often seek it out, and it is usually calm around people who keep a respectful distance. Old stories of giant octopuses dragging divers underwater belong to fiction; in reality this octopus would far rather hide than fight.