Humboldt squid's impressive dives

The energetic world of Humboldt squid has been detailed in new tracking studies that follow the creatures as they dive and climb through the ocean. The animals are found in warmer waters of the eastern Pacific and live an up-down existence as they follow prey. Julia Stewart from Stanford University fitted tags to the cephalopods, and found them to be spending many hours in very oxygen-poor California waters. Ms Stewart spoke about her work at the biennial Ocean Sciences meeting. The tagging study followed the creatures as they dove hundreds of metres into the deep during the day, only to return to surface waters at night. "We've seen them make really impressive dives up to a kilometre and a half deep, swimming straight through a zone where there's really low oxygen," the Hopkins Marine Station researcher said. "They're able to spend several hours at this kilometre-and-a-half-deep, and then they go back up and continue their normal daily swimming behaviour. It's just a really impressive, really fast, deep dive through what is quite a harsh environment." Humboldt are found predominantly in waters off Mexico and further south, but in recent years have been extending their range, on and off, into the California current. There have even been sightings as far north as Alaska. The squid are voracious. They capture their prey with their tentacles and suckers and rip it apart with their powerful beaks. Like other cephalopods, Humboldt squid can change colour, flashing bright red when angered or excited - giving rise to their nickname 'the red devil'. Generally, they will eat small fish, but will take larger organisms in the California current such as rockfish, Pacific hake and salmon smolts. Tags that the team attached to the squid record temperature and depth, and stay on the animal for just under a month before popping off and floating to the surface. When in sight of a satellite, the tags then relay their data back to the researchers. The California current has a band of low-oxygen water at a depth of more than 500m and the researchers were intrigued to see how the animals would cope with it. "It's amazing," said Ms Steward. "This is an animal you'd think would require a lot of oxygen and we see it swimming at pretty comparable rates to what we see it swimming in the highly oxygenated water. "It seems they're somehow able to suppress their metabolism when they're in low oxygen, but they're by no means lethargic. They're swimming around quite well." The animals may swim at 3m/s in surface waters, but even in the deepest depths they are still moving at 1-2m/s. "They're certainly not drifting around," said Steward. Humboldt represent the largest invertebrate fishery in the world. At the moment, this commercial activity does not extend as far north as California, simply because the animals' presence there is not regular enough. But were this to change, the type of research conducted by the Hopkins Marine Station would help determine how such as fishery off the US coast could be managed.