![]() ![]() Some of that oxygen-depleted water then flows north. More organic material means more decay and more oxygen removed from the ocean. ![]() The second possibility: increased productivity. ![]() The warmer and more buoyant surface then inhibits oxygenation of cooler waters below. An ocean that warms from the top down becomes stratified, like a layer cake. There are two possible explanations for this. The planet has warmed in the past 30 years and, generally, sediment cores indicate that the warmer Earth becomes, the larger this eastern Pacific hypoxic zone grows, says Francisco Chavez, a researcher with the Monterey Bay Aquarium Research Institute in Moss Landing, Calif. As this organic material sinks, it decays, sucking oxygen from the water and creating one of the largest hypoxic zones in the world. And it’s further leached of oxygen when organic detritus drops from the highly productive surface waters of the tropical eastern Pacific. Some of the deep water along the west coast of North America originates off the coast of equatorial South America, where the water is already “old,” meaning that it hasn’t been in contact with the atmosphere for many years. “I would suggest that would be in response to hypoxia.” This may explain why some fish species off the coast of British Columbia have moved to shallower areas, and, in some cases into Alaskan waters, says Mr. For these species, the ocean has effectively become 246 feet shallower in the past quarter century. Most sea life that has gills prefers to avoid these hypoxic waters. And the top edge of this low-oxygen zone has advanced upward at an average rate of almost 10 feet per year. At depths between 656 and 1,640 feet, areas of the north Pacific have lost between 1 and 2 percent of their oxygen each year during the past 25 years, says Frank Whitney, a scientist emeritus with Fisheries and Oceans Canada in Sidney, British Columbia. But for the past 50 years in the Pacific Ocean, this layer has become less saturated with oxygen and moved upward. “It’s this scary trend.”Īn oxygen-depleted layer of water exists naturally many hundreds of feet below the ocean surface. 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.įrom Chile to Alaska, the low-oxygen layer “has started to move closer to the surface,” says Louis Zeidberg, a researcher at the University of California, Los Angeles. But in the absence of concrete evidence of overfishing, scientists have since looked to changing environmental conditions for an explanation. Originally, some thought that the squid were growing more numerous because overfishing had reduced their predators and competitors, such as tuna. 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. Scientists, meanwhile, ponder what the dramatic range expansion of a species usually confined to lower latitudes implies about the Pacific Ocean in general. Hake, for example, a major Pacific fishery, has declined since the squid arrived. “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.įishermen 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. And no one had ever seen them as far north as Alaska. But never in numbers comparable to what scientists observed now – schools many hundreds strong. There were accounts from the 1930s of the creatures in Monterey Bay. When scientists dug through historical records, they discovered that the squid’s northward advance wasn’t entirely unprecedented. 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. 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.Īnd indeed, within two years, the Humboldt squid – Dosidicus gigas – had disappeared from central California waters.īut in 2002 – another El Niño year – they reappeared. An unusually strong El Niño event had warmed the eastern Pacific. 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. ![]()
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