Seventeen years ago, Alex Kerstitch and three other photographers headed out to the Sea of Cortez on Mexico's Pacific coast to try to document the behavior of squid in their natural habitat. During one night dive, a passenger aboard the ship hooked a 14-foot thresher shark, and the four photographers jumped in. As the photographers' flashes went off, they noticed dozens of other lights streaking around them in the water. One of the red and white streaks—a jumbo squid more than six feet long—flung itself onto the weary shark, ripping a fist-sized chunk of flesh from its head. Then a tooth- and sucker-tipped tentacle lashed out and grabbed Kerstitch’s head and swim fin, pulling him down toward its birdlike beak. Kerstitch frantically dug his fingers into the squid and it released him long enough for him to scramble back onto the boat.
This jumbo squid attack would have been impossible only a few years ago,as the squid's normal habitat has always been further south. But over the last few years, millions of jumbo squid—often called red devils, or Humboldt squid—have taken up permanent residence off the coasts of California in the Northern Hemisphere and Chile in the Southern. Sightings have been reported as far north as Alaska, where wolves gnaw on the washed-up carcasses.
Why Dosidicus gigas has made its recent move to higher latitudes is something of a mystery. A new study in this week’s issue of Proceedings of the National Academy of Sciences (PNAS) says a combination of factors, including changes in the global climate and fishing practices, have caused the jumbo squid population to grow and expand its range.
Since the squid are originally from lower latitudes with warmer waters and the most recent invasions were during El Niño events in 1997 and 1998 and in 2002 and 2003, the researchers originally suspected global climate change. Buta recent jumbo squid tagging study by William Gilly at Stanford University showed that the cephalopods routinely survive 50-degree temperature fluctuations in a single day, suggesting that relatively gradual global warming might not have that much effect.
Humans may indeed be causing the boom in jumbo squid but by a separate mechanism, according to Monterey Bay Aquarium Research Institute scientist Bruce Robison, lead author of the PNAS paper. “We think one of the main drivers behind the population expansion is the overfishing of tuna,” he says. The decrease in tuna leaves more food for squid, which typically share the same diet, and also saves juvenile squid—a favorite meal of large tuna—from predation. Unfortunately for fishermen, jumbo squid—which eat 1-2 pounds and grow up to a full inch per day—are now tearing into stocks of valuable hake, rock fish, and anchovies.
While the jumbo squid is unlikely to replace the economic or culinary value of the fish it replaces or consumes, it could at least mitigate the loss. Already, the fishing industry pulls in more jumbo squid by weight than any other marine invertebrate. Each year fishing ships, mostly from Asia, land an estimated 700,000 to 800,000 pounds, which ends up on plates as calamari steaks instead of the much smaller calamari that comes from the generic squid. In the West, most of the jumbo variety—roughly 100,000 tons a year—are caught by a growing number of sport fishermen centered around Santa Rosalia, California. “There could be a commercial jumbo squid fishery off California,” says Robison. “The recreational fishery isn’t making much of a dent in their population.”
As for Alex Kerstitch's unfortunate run-in with a jumbo squid in the Sea of Cortez, such attacks are generally very rare. “I know some people who have had incredible experiences swimming with jumbo squid,” says Louis Zeidberg, a former MBARI researcher now at Gilly’s lab. “But if you chum the water they get aggressive. It would be like me walking into a bad neighborhood and shouting expletives.”