Scientists prepare for humpbacks' survival
Every year 2,000-3,000 whales migrate to Hawaii to breed, calve and nurse their young
February 26, 1999
Web posted at: 3:45 PM EST
The mating habits of humpback whales, along with their feeding routines, migration routes and parenting skills, are a matter of deep interest to marine scientists at Hawaii's National Marine Sanctuary.
"Expanding our present understanding of the humpback's vital life rates (age at sexual maturity, age-specific mortality, survivorship rates and longevity), abundance, distribution, movement, behavior, and how these factors relate to its habitat, is absolutely crucial to the whale's survival," says Allen Tom, liaison for the Hawaiian Marine Sanctuary.
At one point in time, humpback whale breeding grounds could be found in all the worlds' oceans. Today there are three distinct and reproductively isolated groups inhabiting the North Pacific, North Atlantic and Southern oceans. They are all endangered.
Most humpbacks live in recognized "communities," wintering and summering in the same places every year. Two-thirds of the North Pacific population returns each year to Hawaii, leaving their feeding grounds in Alaska in October to travel 3,500 miles to breed, calve and nurse their young. They make the return trip to Alaska in May.
Hawaii's humpbacks were relatively safe during the peak whaling years of the late 19th and beginning of the 20th century because they were both fast and had less whale oil than other types of whales. However, once sperm whales, Northern right whales and blue whales had been fished to the brink of extinction, humpbacks were what was left, and between 1905 and 1965, the North Pacific humpback whale population was reduced from approximately 15,000 to about 1,000.
To help the population rebound, the United States established a Humpback Whale Marine Sanctuary off the coasts of Hawaii, and has continuously supported research there. Scientists do know that both males and females reach sexual maturity between the ages of five and nine and that, in the world of humpback whales, females do the choosing. Macho posturing, frequently seen among other species during the mating ritual, is not as much of a factor among humpback males. At their most aggressive, males bump away a rival. More often they blow a thick curtain of bubbles to hide their intended mate.
In addition, the female humpback, if irritated by her mate, shows her displeasure by breeching or swimming away and hiding under a boat. How often mating occurs, what conditions improve reproductive success, pregnancy rates, and calving intervals are all still more or less unknown.
The National Marine Fisheries Service wants the Hawaii population of humpback whales increased to 9,000 animals before its endangered status is reconsidered. Recent studies indicate that while the population may be growing -- albeit ever so slowly -- calf mortality as a result of entanglement in fishing lines and collisions with boats is increasing. With a life expectancy of 30 to 40 years, high calf mortality is a worrying sign.
"We need to know what their songs mean, what brings them back to Hawaii, and what we can do to improve their ability to reproduce. As much as anything, though, the need for increased public awareness and continued support for research is imperative," Tom said, "if we are to preserve these magnificent animals."
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