URI researcher sheds light on 'man-eating' squid; finds them timid, non-threatening

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"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. 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," Seibel said.

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 five or six 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 more than just a personal test. It was part of a scientific examination of the species 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 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, man-eaters they are not. 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.

The highlight of Seibel's research cruise with colleagues from the Monterey Bay Aquarium Research Institute was diving with the impressive animals. Other divers participating were Lloyd Trueblood of URI, Steve Haddock of MBARI, 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."

According to Seibel, there have been many active discussions among biologists and the dive community about the safety of diving with Humboldt squid. As a result of his experience, the URI scientist 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.

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

University of Rhode Island