How Big Is a Giant Pacific Octopus? Size and Records

How big is a typical giant Pacific octopus?

The giant Pacific octopus (Enteroctopus dofleini) is the largest octopus species, but “largest” does not mean monstrous. Adults are often said to weigh around 15 kg (33 lb), and an octopus of that size is already a large, impressive animal underwater.

In 1976, a fisheries biologist summarizing knowledge of the species for the US National Marine Fisheries Service wrote that most giant Pacific octopuses weigh less than 32 kg (70 lb) and have a stretched length of 4.6 m (15 ft) or less.

Why is an octopus so hard to measure?

An octopus has no skeleton, so its size changes with how it is handled. Out of water, a living octopus slumps into a soft heap; hung up by the body, its arms stretch far beyond their natural length. Scientists therefore distinguish several measurements:

• Mantle length: the length of the body sac, the most reliable measure.
• Total length: from the tip of the mantle to the tip of the longest arm.
• Arm span or radial span: from one arm tip to the opposite arm tip, roughly double the arm length.

Weight is the best single measure of how big an octopus really is, but it is rarely recorded for wild giants. Most dramatic size claims give a huge arm span with no weight, or a round-number weight with no measurements, which makes them impossible to check.

What is the biggest giant Pacific octopus on record?

The record books contain three kinds of giant: measured, weighed and merely reported.

• Longest span measured: in 1874 the naturalist William Healey Dall collected an octopus in the harbor of Iliuliuk on Unalaska Island, Alaska. When it was hung up after death, he measured an arm span of at least 9.8 m (32 ft). Its arms were very slender toward the tips and its body was only a little over 30 cm (1 ft) long, so it was far lighter than the span suggests.
• Reported heavyweights: in the 1950s a Canadian commercial diver told a biologist that he had captured an octopus of 272 kg (600 lb) with a span of 9.8 m (32 ft), and later accounts suggest he only saw it and never brought it in. A 1945 specimen from Santa Barbara, California, was reported at 182 kg (402 lb), but the surviving photograph appears to show a large but ordinary octopus.
• Heaviest confirmed: according to the octopus researchers James Cosgrove and Neil McDaniel, the heaviest confirmed live weight is about 71 kg (157 lb), for an animal collected in the mid-1960s.

The figures of 272 kg and 9.6 m that appear in many encyclopedias and quiz books trace back to that single unverified report.

Are giant Pacific octopuses getting smaller?

No octopus approaching the giant sizes of those old reports has been documented since the mid-20th century. Commercial octopus fishers interviewed for a 2009 book on the species said they had not caught a single animal heavier than 57 kg (126 lb) in 20 years, among many thousands. At the Seattle Aquarium, biologists who fed captive males as much as they would eat raised one to a peak of 43 kg (95 lb).

There are three possible explanations. The old giants may simply have been exaggerated. Fishing may remove large animals before they reach full size. Or pollution may play a part: researchers have found heavy metals and PCBs in wild octopuses, apparently from crabs they eat, and in one preliminary study, aquarium octopuses fed local crabs matured at smaller sizes. None of these ideas has been proven.

How fast does a giant Pacific octopus grow?

Growth is astonishingly fast. A hatchling weighing about 0.03 g (0.001 oz) can reach 10–40 kg (22–88 lb) within its short life of three to five years, gaining close to 1 percent of its body weight per day. Because it is cold-blooded, it spends little energy on keeping warm and can turn much of its food into body mass. That food is mostly crabs and clams, as described in what do giant Pacific octopuses eat?

Growth only stops when the octopus breeds. Males decline and die within a few months of mating, and females die after guarding their eggs for about half a year, so a giant Pacific octopus is usually at its largest just before it breeds.

How does it compare with other big octopuses and squid?

The giant Pacific octopus has one serious rival among octopuses: the seven-arm octopus (Haliphron atlanticus), a jelly-like species of the open ocean. In 2002, fishermen trawling off New Zealand caught an incomplete female of 61 kg (134 lb), which scientists estimated would have weighed about 75 kg (165 lb) and measured about 4 m (13 ft) when complete. That puts the two species roughly level, and only the giant Pacific octopus has confirmed weights above 70 kg (154 lb).

Other octopuses are much smaller. The common octopus of Europe rarely exceeds 10 kg (22 lb), and many octopus species weigh less than 1 kg (2.2 lb).

Squid are another matter. The giant squid reaches about 12–13 m (39–43 ft) including its tentacles and up to about 275 kg (606 lb), and the colossal squid of the Antarctic weighs up to about 495 kg (1,091 lb). For the other differences between the two groups, see octopus vs squid.