Giant squid have been found in every ocean of the world, but a recent DNA project shows that the giant squid are a single species.
Not much is known for certain about giant squid. More than one hundred specimens and parts of specimens have been found. Most of them washed up on shore or were found partially digested inside whales.
Giant squid grow up to 43 feet long and weigh as much as 660 pounds. Although they are so large, they have been difficult to find and study because they stay in deep waters, ranging from 975 feet to 3250 feet deep. They seem to prefer colder latitudes, since few have been found in tropical areas.
Because of the lack of giant squid in tropical areas, many scientists had believed that there were at least three separate species, determined by geography – one in the Atlantic Ocean, one in the northern Pacific Ocean, and another in the Southern Ocean. However, biologist Thomas Gilbert and colleagues recently sequenced DNA from all the known samples of giant squid and found very little genetic variation among them.
The reasons for so little genetic variation are uncertain. One possibility is that of a genetic bottleneck. Something – disease, climate change – might have killed off most of the population, so that today’s giant squids are descended from only a few individuals. It’s also possible that something allowed the species to flourish recently, resulting in a population explosion. Suggestions include whaling, which would have reduced predation on the squid, or abundant food or climate change.
A third possibility is that giant squid travel long distance in their lives, thoroughly mixing the breeding population. Little is known about their reproductive habits. They may only have one or a few nurseries in the world.
The videos below show footage excerpted from a documentary on Discovery UK.