Orange County Register

FORTY WINKS: Northern elephant seals at rest. Image courtesy of Wikipedia's Creative Commons

Big, blubbery Northern elephant seals sometimes flop on to the rocks in the more isolated coves of Laguna Beach and sleep, which apparently is only part of the way they refresh themselves. New research led by Japan’s Hokkaido University says its possible that the animals also may sleep while they do “drift diving” while migrating between California and Alaska. The behavior seems to occur where the ocean is comparatively deep, which would include the waters between Santa Catalina Island and the mainland. There are areas where the channel is at least 2,000 feet deep.

The summary portion of the new study says: “During their long migrations through the Pacific, northern elephant seals,Mirounga angustirostris, never haul out on land and they rarely spend more than a few minutes at a time at the surface. They are almost constantly making repetitive, deep dives, raising the question of when do they rest?

“One type of dive, the drift dive, characterized by a time-depth profile with a phase of lower than average descent speed is believed to be a resting dive. To examine the behaviour of seals during drift dives, we measured body position and three-dimensional diving paths of six juvenile seals. We found that seals rolled over and sank on their backs during the drift phase, wobbling periodically so that they resembled a falling leaf. This enabled seals to drastically slow their descent rate, possibly so that negatively buoyant seals can rest without ending up in the abyss. This reduces the work required to return to the surface to breath, and allows them time to rest, process food or possibly sleep during the descent phase of these dives where they are probably less susceptible to predation.”

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