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Why Gray Whales Died In Record Numbers

Between 1999 - 2001 Gray Whales died in unprecedented numbers along the western coast of North America from Baja California to Alaska. The reason for this remains a mystery but there are indicators which hold alarming implications for human beings as well as marine mammals.

Background - Gray whale populations enjoyed a substantial growth after a ban was imposed on commercial whaling in 1947, with numbers eventually surpassing 28,000 in the eastern Pacific. But while these numbers were attained in the mid 1990's they began dropping again in 1998 due to a sharp increase in strandings which continued into 1999, when there was a total 274 deaths, twice the number in any previous year dating back to 1985! This is a tragic turn of events for such a magnificent animal that is prominent in the minds of Californians as a rightful dweller and spectacular legend in these waters.

The Theory - Scientists have officially designated the whale strandings an "unusual mortality event", and suggest they are the result of starvation. The causal relationship may be that the most recent El Nino in 1997 caused sea temperatures to rise, producing a negative impact on food supplies for many marine mammals. partially as a result of that, studies have shown that the benthic amphipods that gray's feed on in the Bering and Chukchi seas off Alaska have been declining significantly since the mid-1980's.

The equation appears simple; less food available and more mouths to feed means that some individual Gray whales simply cannot get the nutritional sustenance they need to survive. This is especially true if you consider that the summer feeding in the Arctic must sustain an 80,000 pound animal on a 7,000km journey, (the distance it migrates to the southern breeding lagoons). Initially the stranded bodies were mostly young individuals in an emaciated condition, indicating the predicted lack of stored energy.

This theory, however, came into question in 2000 when more deaths occurred, but this time the bodies were mostly healthy looking adults with a substantial looking layer of blubber.

Gray whales feed by scooping up large mouthfuls of substrate including water, mud and the amphipods, which they filter through their massive baleen scales to leave behind the edible material. The tiny amphipods are also filter feeders, siphoning plankton out of the water. Many of the gray whales feed in Alaska but portions of the population summer off British Columbia, others off the coast of Washington State and will others off California.

Bottom feeders are especially susceptible to ingesting the toxic substances which fall to the bottom of the sea, especially in areas where there is intensive industry and agriculture. It may be significant that gray whale deaths have occurred in especially large numbers in Puget Sound and San Francisco Bay.

According to Dr. Frances Gulland, Director of Veterinary Science at the California Marine Mammal Center near Sausalito, there "was a huge clustering in the Bay Area" of dead gray whales - about 30 animals between April 1 and May 31 - despite an otherwise uniform distribution along the rest of the coast. Again, they were not thin, but in good condition, so it appears there may be something other than a lack of food that is affecting them.

Alternative explanations include parasitic infections, biotoxins, contaminants, viruses, bacterial infections or fisheries and boat interactions. But finding out exactly what is causing these high levels of mortalities is proving to be very difficult. Their bodies aren't all washing up to shore, which means that Gulland and her colleagues often have to don wet suits and climb on top of floating carcasses to obtain samples. Aside from dealing with delays in notification and a lack of sites upon which to conduct necropsies, the bodies may also be decomposed making reliable analysis extremely difficult.

Are Gray Whales foraging more widely and utilizing additional feeding strategies? In response to lack of food in their traditional feeding areas gray whales have been seen filter feeding, sometimes in the presence of blue whales and humpbacks. They are also being seen in areas heretofore unreported - the northern Sea of Cortez for example.

These forced changes of habit may also be the result of overpopulation, but the fact remains that gray whales are probably eating different foods to their normal diet in places they don't normally go. This may put the whales in harm's way. Some grays have been seen under the Golden Gate bridge which means that they are having to deal with boat traffic (one body was found with propeller marks all along it's back, and another was hit by a tug).

The starvation theory may only be part of the puzzle. While the current bodies appear to have a healthy layer of fat on them, their looks may be deceiving. According to Bruce Mate, Professor of Fisheries and Wildlife at Oregon State University, a thick layer of blubber does not always contain that crucial fat content. He has analyzed a number of still-born gray whale calves and found their normal looking layer of blubber does "not have enough fat in it to fry an egg," but consists of mainly collagen and water.

A special study group of marine mammal experts has convened to exchange information in an effort to determine the causes of the extraordinarily high levels of gray whale deaths. Their results are eagerly awaited as the gray whales migrate along the west coast.

Helpful actions - - If you live in the area and you see any stranded whales or other marine mammals, please call the Marine Mammal Center as soon as possible. (phone: 415 289 SEAL)

 

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