Collins is especially interested in clues the images might provide to the way giant squid swim and hunt in the deep ocean.

　　"Seeing the animals on film gives you a tremendous insight into how they live down there," he said. "It shows they are pretty active animals, and that answers a big question that's been out there for some time."

　　Collins says there were two competing schools of thought among giant squid experts.

　　"One was the idea that [giant squid] were fairly inactive and just drifted around, dangling their tentacles below them like fishing lures to catch what came by," he said.

　　"The other theory was that they were actually quite active. This new evidence supports this, suggesting they are active predators which can move reasonably quickly."

　　"The efforts the squid went to untangle itself [from the baited fishing line] also shows they are capable of quite strong and rapid movement," he added.

　　The study team reports that the severed tentacle repeatedly gripped the boat deck and crew after it was hauled aboard. The squid's tentacles are armed with suckers, each ringed with tiny teeth to help snare prey.

　　Measuring 18 feet (5.5 meters) long, analysis of the tentacle confirmed it came from a giant squid and allowed the researchers to estimate the total length of the animal.

　　But the researchers caution that their data assume the tentacle was severed at it base. If not, the squid may have been considerably larger. The longest giant squid on record measured 59 feet (18 meters), including its two elongated tentacles.

　　Shedding Light on Giant Squid

　　Giant squid, along with their close cousins colossal squid (Mesonychoteuthis), have the largest eyes of any animal.

　　"Giant squid do have particularly large eyes, which would suggest vision is important to them. Having a large eye isn't unusual in deep-sea animals-you see it quite often in fish."

　　The fact that the animal caught on film was swimming in total darkness suggests the species detects prey using alternative light sources. "The only light down there is likely to be light produced by other animals," said Collins of the British Antarctic Survey.

　　The Japanese team thinks that research techniques similar to their own could be used to bring about more close encounters with giant squid. Ellis of the American Museum of Natural History agrees.

　　"I'm sure we can learn a lot from an analysis of these images," he said. "And now that we have an idea of where to look for [the squid], we will undoubtedly get more pictures."

　　1. The passage talks mainly about the studying of a live giant squid by American scientists.

　　2. The giant squid was photographed 2,950 feet beneath the North Pacific Ocean.

　　3. The observations by Tsunemi Kubodera and Kyoichi Mori was reported in the journal Proceedings of Royal Society B.

　　4. The Japanese film is a breakthrough in the study of the giant squid's life and habits.

　　5. There are three competing schools of thought among giant squid experts.