The squid are believed to live at depths of 660 to 2,300 feet (200 to 700 meters). They may be elusive in some parts, but they're not rare. Gilly estimates that 10 million squid may be living in a 25-square-mile (65-square-kilometer) area outside Santa Rosalia, Mexico.
"There is probably an almost unimaginable number of Humboldt squid if you consider their entire rangeChile to California and over halfway to Hawaii on the Equator," he said.
Every night, hundreds of Mexican fishermen head out to the rough seas in pangas, small skiffs, to fish for jumbo squid. It's no easy task. The catch is heavy, and every squid must be caught on a hand line.
But the harvest is lucrative. Humboldt squid are considered a delicacy in Japan. Each boat, manned by two or three fisherman, typically brings back a metric ton (2,200 pounds) of squid every night.
Scientists believe the Humboldt squid, like most predators, focus their diet on the most easily captured prey, in their case lantern fish and sardines. In turn, the squid is preyed upon by large fish such as marlin and swordfish, and it's a main staple of sperm whales.
The jumbo squid are also known to eat each other, at least when one squid is impaired on a fishing line. Such cannibalistic behavior has fueled the squid's reputation as a bloodthirsty sea creature.
Many fishermen are terrified of the squid. There are numerous stories floating around of fishermen falling overboard and being dragged down by jumbo squid.
During the filming of Devils of the Deep, cameraman Bob Cranston found himself entangled in several squid. The incident luckily ended without injuries, and provided for some extraordinary footage.
Gilly says the squid's ruthless reputation is unwarranted.
"I've been snorkeling with them at night in just shorts and T-shirt," he said. "The squid would swim up to the surface, reach out with their arms and gently touch my extended hand. To meet them like this and shake hands was truly amazing, like meeting an extraterrestrial being."
Tag and Recapture
A greater knowledge of the Humboldt squid may bring economic benefits. The entire economy of fishing towns like Santa Rosalia depends on squid, with fishing and packing operations providing local jobs.
"This issue of commercial relevance has international as well as local implications," said Gilly. "Where do the squid that are being caught in the Gulf spawn? Are there more than one breeding population? We don't know, and such questions underlie some thorny issues in other fisheriessuch as salmon or tuna."
From his tag-and-recapture studies, Gilly has learned that the squid carry out a seasonal migration of more than 100 miles (160 kilometers) across the Gulf of California, between Santa Rosalia on the Baja peninsula and Guaymas on the Mexican mainland. They spend the day about 800 feet (250 meters) deep, rising at dusk toward the surface where they feed at night.
"We don't know what they are doing during the day," said Gilly. "This is especially interesting because the water at these depths in the Gulf has almost no dissolved oxygen in it. From what we know about squid respiratory physiology, they should not be able to survive the conditions there."
Scientists also don't know why the squid inhabits an area for some time, then disappears only to emerge somewhere else in huge numbers. Some experts believe that ocean-going squid like the Humboldt are increasing in numbers as fin-fish populations around the world decline.
Like other scientists, Gilly believes we have only skimmed the surface of what the oceans really hold, and that many other sea creatures are still waiting to be found.
"Many of the so-called discovered species are so mysterious that they are little more than exotic Latin names," he said.
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