Squid invasions signal changes in the Pacific Ocean

When large numbers of jumbo squid first showed up in California’s Monterey Bay in 1997, scientists weren’t sure what had brought the cephalopod that far north. An unusually strong El Niño event had warmed the eastern Pacific. But the squid, dubbed el diablo rojo – the red devil – in its native waters off the coast of Mexico, didn’t typically venture farther north than Baja California.

And indeed, within two years, the Humboldt squid – Dosidicus gigas – had disappeared from central California waters.

But in 2002 – another El Niño year – they reappeared. This time, they took up permanent residence and pushed even farther north – past Oregon, Washington, and British Columbia, until, by 2004, fishermen near Sitka, Alaska, were hauling them in.

When scientists dug through historical records, they discovered that the squid’s northward advance wasn’t entirely unprecedented. There were accounts from the 1930s of the creatures in Monterey Bay. But never in numbers comparable to what scientists observed now – schools many hundreds strong. And no one had ever seen them as far north as Alaska.

“This occurrence has gotten weird enough to not really make it into the realm of ‘normal,’ ” says John Field, a fisheries biologist with the National Oceanic and Atmospheric Administration in Santa Cruz, Calif.

Fishermen worry that the squid, a voracious predator weighing up to 110 pounds and reaching more than six feet in length, will diminish valuable fish stocks.

Hake, for example, a major Pacific fishery, has declined since the squid arrived.

Scientists, meanwhile, ponder what the dramatic range expansion of a species usually confined to lower latitudes implies about the Pacific Ocean in general.

They’re gradually piecing together a story of natural cycles that, together with climate change, have altered the eastern Pacific in a way that favors jumbo squid.

Oxygen-depleted waters expand

Originally, some thought that the squid were growing more numerous because overfishing had reduced their predators and competitors, such as tuna. But in the absence of concrete evidence of overfishing, scientists have since looked to changing environmental conditions for an explanation.

Now, they think the squid are moving both north and south from their equatorial stronghold – they’ve also become more abundant in Chilean waters – because conditions they’re uniquely adapted to – low-oxygen, or hypoxic, water at a certain depth – are expanding poleward from the tropics as well.

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