Wednesday April 19 5:35 PM ET
By Allan Dowd
VANCOUVER (Reuters) - Gray whales are again washing up dead on North America's Pacific coast, but experts said Wednesday they do not know if it is evidence of a problem or if the whale population has returned to a healthy balance.
Nearly 30 gray whales have been found dead from California to British Columbia in recent weeks as the mammals make their annual migration from their breeding grounds off Mexico to summer feeding grounds in the Bering Sea off Alaska.
At one time, gray whales had been hunted nearly to extinction, but researchers estimate there are now about 26,000, close to the same number believed to have existed before large-scale commercial whaling began in the 1800s.
Trade in the gray whale has been outlawed since 1949, allowing the population to recover.
The 273 gray whales found dead last year along their migration route was five times the number normally found, so researchers are not surprised to hear of deaths again this year, said Peter Ross of the Institute of Ocean Sciences in Victoria, British Columbia.
``We could be seeing in these strandings that they've reached equilibrium in their population,'' Ross said.
But researchers are also concerned the deaths could be the result of environmental changes in the Bering Sea that have caused a drop in the whale's primary food supply -- tiny amphipod crustaceans.
The whales, which can weigh up to 36 tons and live as long 60 years, spend the summer in the Bering's cold waters eating and building up a reserve of fat they live on for the rest of the year.
The Bering food supply, used by whales and other animals such as sea lions, has been dropping for two decades but researchers do not know why, said Donald Schell of the University of Alaska in Fairbanks.
``It may be because the whales are beating it down...It may be because of environmental reasons,'' Schell said.
Many of the adult whales found dead last year were emaciated, indicating they had not been able to eat enough to make the journey. Tissue samples have been taken from the animals discovered this year.
Scientists are also sampling dead whales' fat for toxins. But Ross, a toxicologist, said he does not believe that pollution is the direct cause of death of the animals discovered so far.
Researchers acknowledge that since the deaths occur at sea, the carcasses discovered washed ashore represent only a small portion of the actual death toll.
``I'm not too concerned about the state of the gray whale population at the moment. On the other hand, I would be concerned if these sentinels are telling us about the state of the oceans,'' Ross said.