National Geographic : 1984 Aug
Playground for whales, a stretch of water inJohnstone Strait serves as a "rubbingbeach"for a killer that scratches itself on the smooth stones (below). On anotherpart of the same beach two young whales circle each other (right) in a bit of underwater horseplay.Killers gather in "core areas" like this to romp and relax together. Researchersdon't know why the whales like to rub their sensitive skins on the bottom, but it may be a form of grooming. Maturingat about ten years of age, females average one birth per decade, though some calve as often as every three years. Gestationaverages 16 months. Measuringabout eightfeet at birth, bulls can grow to 25 feet and 228 weigh as much as six tons. Cows may reach 21 feet and four tons. Orcas rest togetherfor periods lastingfrom a few minutes to four hours. Staying in tight groups near the surface, they seem to synchronize their movements, often coming up for air at the same time. They may not use their sonarduring such periods of rest, but insteadkeep track of one another through sight and touch. Researchers speculate that this subdued activity probably substitutesfor sleep. Pods tend to keep to themselves during the winter and spring months. But in the summer and fall they sometimes join together for hours at a time to socialize in large "superpods."