Jumbo Squid Scare Californians But Aren't Man-Eaters

Humboldt Squid (Dosidicus gigas) photographed by Monterey Bay Aquarium Research Institution’s remotely operated vehicle Tiburon at a depth of about 300 meters over Davidson Seamount, off the Central California coast. (Image credit: courtesy of the Monterey Bay Aquarium Research Institution)

Carnivorous jumbo squid have been washing up on San Diego beaches and swarming in Southern California's coastal waters, freaking out scuba divers and bathers this month, but a biologist now says these beasts are not man-eaters, despite concerns expressed in the media.

Reports started coming in earlier in July that dozens of the squid, also known as Humboldt squid, were washing ashore and interacting with divers. Jumbo squid can grow up to 7 feet long and usually prefer to live in deeper waters. Lately, off-shore divers have reported seeing large groups of the squid, which can swim as fast as 15 mph.

University of Rhode Island biologist Brad Seibel, who has dived with jumbo squid several times, called the reports "alarmist."

For years, Seibel has heard stories claiming that Humboldt squid will devour a dog in minutes and could kill or maim unsuspecting divers.

"However, I want to spread the word that [Humboldt squid] aren't the aggressive man-eaters as they have been portrayed," Seibel said.

"Private dive companies in Mexico play up this myth by insisting that their customers wear body armor or dive in cages while diving in waters where the squid are found," Seibel said. "Many also encourage the squid's aggressive behavior by chumming the waters. I didn't believe the hype, but there was still some doubt in my mind, so I was a little nervous getting into the water with them for the first time."

Jumbo squid have pulled with their tentacles at divers' masks and equipment, and at one diver's arms, according to the San Francisco Chronicle. Scientists have no firm idea why the squid have suddenly invaded San Diego's coastal waters, but it could be anything from global warming to a shortage of food or a decline in jumbo squid's predators, according to the newspaper.

Scuba diving at night in the surface waters of the Gulf of California in 2007, Seibel scanned the depths with his flashlight and saw the shadows of Humboldt squid far in the distance.

After he got up his nerve, he turned off the light. When he turned it back on again 30 seconds later, he was surrounded by what seemed like hundreds of the squid, many just 5 or 6 feet away from him. Most were in the 3-4 foot size range, while larger ones were sometimes visible in deeper waters. But the light appeared to frighten them, and they immediately dashed off to the periphery.

The URI researcher's dive was part of a scientific examination of the species, which some call "red devil," to learn more about their physiology, feeding behavior and swimming abilities.

Humboldt squid feed in surface waters at night, then retreat to great depths during daylight hours. "They spend the day 300 meters [nearly 1,000 feet] deep where oxygen levels are very low," Seibel said. "We wanted to know how they deal with so little oxygen."

Seibel said that while the squid are strong swimmers with a parrot-like beak that could inflict injury, they are not man-eaters.

Unlike some large sharks that feed on large fish and marine mammals, jumbo squid use their numerous small, toothed suckers on their arms and tentacles to feed on small fish and plankton that are no more than a few centimeters in length.

Seibel's dives were part of a research cruise with colleagues including Lloyd Trueblood of URI, Steve Haddock of the Monterey Bay Aquarium Research Institute, and Alison Sweeney of the University of California, Santa Barbara.

Seibel was surprised by the large number of squid he encountered, which made it easy to imagine how they could be potentially dangerous to anything swimming with them. Their large numbers also made Seibel somewhat pleased that they appeared frightened of his dive light. Yet he said the animals were also curious about other lights, like reflections off his metal equipment or a glow-in-the-dark tool that one squid briefly attacked.

"Based on the stories I had heard, I was expecting them to be very aggressive, so I was surprised at how timid they were. As soon as we turned on the lights, they were gone," he said. "I didn't get the sense that they saw the entire diver as a food item, but they were definitely going after pieces of our equipment."

There have been many active discussions among biologists and the dive community about the safety of diving with Humboldt squid, Seibel said.

As a result of his experience, Seibel is preparing a formal report with his recommendations for safely diving with the squid, including suggestions to always carry a back-up dive light and to be tethered to a boat. Any time humans enter the habitat of a large animal, there is potential for dangerous interactions, he said, so divers should use caution.

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