Changing tides below
Humboldt squid's core range used to extend from San Diego across the equator to northern Chile but now stretches from southern Alaska to Chile's southern tip. Off the central coast of California, where the squid were a rare visitor before the year 2002, jumbo squid sportfishing boats now frequently depart.
One factor contributing to the squids' expansion seems to be the eastern Pacific's growing dead zones, where they spend much of the day.
Well-known river-mouth hypoxic zones, such as the dead zone in the Gulf of Mexico, are fed by agricultural runoff and the algal blooms it encourages. But deep-sea low-oxygen zones are naturally occurring, integral parts of larger oceanic systems, where organic matter filters down from highly productive areas only to be consumed by anaerobic bacteria that emit carbon dioxide. In such environments, dissolved oxygen levels are so low that many ocean creatures, such as large predatory fish, have trouble staying for long.
Changes in climate, water stratification, wind patterns and currents in the Pacific might all be playing a role in expanding these hypoxic zones, Gilly explains. Despite their dreary name, these growing dead zones are likely boosting Humboldt squid numbers. In warmer water areas these low-oxygen zones often start 200 meters below the surface and extend in the water column down to about 1,000 meters. Off the coast of California, however, Gilly explains, these zones have historically started at a depth closer to 400 or 500 meters, making them much smaller. But in recent years, "that zone is getting bigger" and low oxygen areas have been growing closer to the surface off the coast of North America. Off Oregon, for example, many of the past summers have brought a new seasonal dead zone close to the coast.
This change has meant less livable ocean habitat for many creatures that depend on well-oxygenated water to survive. But for Humboldt squid the expansion of these dead zones has been a lifeline to new habitats. Gilly and his lab have discovered the squid can hang out hundreds of meters down in areas that hold as little as 10 percent of standard surface oxygen levels for a whole day. In fact, the squid do not just seem to tolerate these harsh aqueous climes, but they appear to actually "have an affinity for and favor" them, Gilly notes.
Just why Humboldt squid are thriving deep in these low-oxygen zones remains a mystery. Scientists speculate that the squid are likely feasting on the many small animals such as krill and lantern fish that are adapted to spend the day there hiding from other predators that are not equipped to spend time in the hypoxic areas. (The squid, along with the smaller fry, tend to surface around sunset and spend much of the evening in higher waters.) "In a way, they're the masters of that universe," Gilly says about the hypoxic zones. "They're the top predators in that world."
These hostile zones also likely afford refuge for Humboldt squid from many of their own predators, such as tuna, billfish and sharks, Field points out. Other researchers have proposed that there might also be some sort of metabolic advantage to staying in those low-oxygen areas, as well. Because low oxygen levels slow many animals down, "you can eat without a lot of effort," Gilly explains.
Researchers have often observed Humboldts feeding in schools, a phenomenon common in many squid species but which can be scary to divers who encounter large numbers of jumbos that can be as big—or bigger—than a human. Although disparate accounts of attacks on divers exist, many experts think the squid are probably investigating the intruders rather than trying to harm them.
Swimming in the dark
Although the squid appear to be in abundance in most areas where they are fished, their actual numbers remain unknown. "We really don't know what the biomass [of Humboldt] is in any of these places," Gilly says.
The expanding hypoxic zones and warming waters that appear to have been a boon to these squid so far are not the only projected climatic changes, however. And other shifts might not bring clear-cut advantages for the jumbo squid. A 2008 study from Proceedings of the National Academy of Sciences found that the projected increase in ocean acidity levels by 2100 might decrease the squids' metabolic rate by as much as 31 percent and cut their activity rate by 45 percent, meaning that they would be not be eating as much. Other observations have contradicted these findings, however, so the effect of ocean acidification will be "important to sort out," Field says—especially if Humboldt squid continue to become increasingly prominent players in the ecosystems.
"It seems pretty clear to me, at least," that climate changes on the whole "seem to be benefiting" Humboldt squid, Field says. But until more research comes in, "the jury's still out" on what the long-term impact on—and of—the squid will be. "We simply don't know," he concludes.
Efforts to count squid and tag them are ongoing in California as well as South America. And an international symposium in La Paz, Mexico, in October will bring experts together to discuss ongoing research in the field.
Gilly concedes it is possible that the more recent observations of the Humboldt's proliferation could have resulted from changes in the squid's behavior or distribution rather than an increase in overall numbers, but he thinks it is more likely there are just more of them. So the question becomes where they might crop up next.
He has a friendly wager (for a six pack of beer) going with a scientist in Russia that the squid will make it to Kamchatka on Siberia's Pacific coast before the men die. With the growing low-oxygen zones under much of that part of the Pacific, "that pathway for them would seem to be there," Gilly says. "They seem to go wherever they want."