National Geographic : 1987 Apr
from the apparently unconcerned female. Four of us crowded around him. With hands shaking, Gerry opened the instrument case. "Look at that!" he croaked, in a voice strained with excitement. There, in a faint trace on the paper strip, was a line represent ing hundreds of dives, many to 300 feet or more. It was hard to grasp the significance of the event. This hundred-pound female fur seal was routinely diving at least ten times deeper than most humans can. But more important, the diving instrument worked. We had a new tool for measuring what seals do at sea. Thanks to Gerry's instrument, and to new ones since, we have learned more about the diving ability of seals in the wild during the past decade than in all the years before. Us ing such instruments, Gerry and I, along with a dozen colleagues, have recently com pared diving in fur seals worldwide. We've found that they are fast divers: Animals weighing 100 pounds can go to 600 feet and back in five minutes or less. Gerry's conclu sion: "Seals are a lot better athletes than most people realize." Further research has taught us a great deal more. Generally, the larger the seal the deeper it can dive. A 240-pound Hooker's sea lion female at Enderby Island dived re peatedly to 1,400 feet. A Weddell seal dived to 1,900 feet, and a northern elephant seal was recorded at an incredible 2,900 feet by Burney Le Boeuf. There are probably spe cies of whales and porpoises that do not dive to such a depth. It appears that seals expend the least pos sible effort when feeding. They can usually find food at less than their maximum depth. Fur seals normally feed on fish or krill at less than 300 feet, Hooker's sea lions feed on squid at about 600 feet, and northern ele phant seals feed, possibly on ratfish, at around 1,500 feet.