The study also revealed that the squid often made rapid nighttime dives from the surface to deeper waters preferred by whales. "One reason squid may be going down there at night is because water near the surface is really warm—up to 82 F—and they may be getting stressed," Gilly explained. "The squid is using energy all of the time, because it has to swim to breathe. So when it gets into really warm water, I think it gets out pretty quickly. These deep dives, therefore, may have some kind of recovery function. We think the stress may be temperature-related, but another factor could be oxygen. It’s possible they could be negatively affected by long exposure to the higher oxygen levels found near the surface."
A stressed-out squid may be an easy target for hungry sperm whales waiting below, according to Gilly. "We propose that jumbo squid are more susceptible to predation while they are recovering at depth immediately after a deep nighttime dive," he explained.
In previous studies, Gilly found that jumbo squid are well adapted to the low-oxygen environment in deeper waters, where they spend most of their time. However, he added, at depths of 800 feet or more, where it’s very cold and oxygen levels are extremely low, the squid’s reaction time, visual acuity and swimming speed may be significantly impaired because of an inadequate supply of oxygen—a condition known as hypoxia.
"Squid need a constant supply of oxygen to support their metabolism," Davis added. "Sperm whales, on the other hand, take the oxygen down with them bound to the hemoglobin in their blood and the myoglobin in their muscles, so they don’t have to worry about hypoxia at depth."
By spending most of their time in cold, deep waters, he noted, sperm whales can take advantage of a vuln