New Method To Determine Gray Whale’s Age Is Crucial To Understanding Population’s Health

Source: Hakai Magazine/Larry Pynn

Photo: Merrill Gosho/NOAA/Wikimedia Commons


If you see a gray whale cruising offshore, it’s fairly easy to guess, based on little more than its size, whether it’s an adult or a juvenile. But without digging through a dead whale’s earwax or examining its ovaries, determining age is surprisingly difficult.

A Canadian researcher has now discovered a novel method to eyeball a gray whale’s age that is much less invasive than existing techniques. By analyzing the relationship between whales’ sizes and their ages, Selina Agbayani, a master’s student at the University of British Columbia (UBC) in Vancouver, has plotted growth curves that describe in detail how gray whales change in length and weight as they age.

To develop the growth curves, Agbayani pored over records of whales slaughtered during the commercial whaling era as well as observations from scientific surveys and strandings. She parsed 903 records: 634 provided specifics on age and length and only 15 noted the whale’s weight.

Agbayani’s study reveals that gray whales don’t follow a simple linear pattern as they grow. When a gray whale is born, it’s roughly 4.6 meters long and weighs one tonne—as much as two concert grand pianos. Consuming about 30 liters of its mother’s rich milk a day, the calf rapidly packs on weight. By nine-and-a-half months, the calf has grown to 8.4 meters and 5.7 tonnes. After this initial spurt, the whale weans off milk and its growth slows.

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Photo: Merrill Gosho/NOAA/Wikimedia Commons

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