Scientists on the US Pacific coast are increasingly observing emaciated grey whales in what they fear is a sign that global warming is wreaking havoc in the whales’ Bering Sea summer feeding grounds.
The scientists fear that the same phenomenon is cutting back reproduction in the Pacific whale population to the point it could be facing a new crisis, after recovering in the mid-1990s and graduating from the endangered species list.
“The grey whales are migrating later, not going as far north, and are producing fewer calves,” Steven Swartz, head researcher with the National Marine Fisheries Service told AFP.
Swartz, who with his team meticulously photograph and identify the migrating whales, estimates that at least ten percent of the population is seriously skinny.
“Instead of looking plump coming off the summer months, they have noticeable depressions behind the head, with scapulas visible through the skin, and concave sections above the tail,” he added. “This is enough to cause alarm.”
Swartz has studied the pacific whale population since 1977 and last saw a major whale die-off in 1999 when an El Nino warming cycle left traditional northern feeding grounds barren and claimed one third of the population.
He has partnered with scientists at the Autonomous University of Baja Sur, Mexico since 1996, keeping tabs on the whales’ calving and migration, the longest of any mammal.
The most recent grey whale survey in 2001 showed a decrease of thirty percent in five years. Researchers are now holding their breaths while final tabulations are completed on a current survey, and are bracing for another drop, said Swartz.
“We have yet to find any indications of disease in the population,” said Swartz. “When times are tough and there is less food out there, the whales do not reproduce. It’s possible that they are birthing somewhere else, but we have a lot of people looking, and we have not found them.”
The San Ignacio lagoon, one of four grey whale breeding grounds off the Pacific coast of Mexico, can be used as a litmus test for the reproductive rate of the species, said Swartz.
In the early 1980s, 350 calves were born in these waters every February. This past winter the number was closer to 100.
The Chirikov Basin in the Bering Sea 10 000 kilometres to the north has long provided the whales the summer food necessary for the long trip south. They gather in the basin to feed on vast beds of calorie-rich crustaceans called amphipods.
But warming temperatures and retreating ice in the Bering Sea has diminished the growth of algae and plankton necessary for the amphipods to thrive. The annual crop of invertebrates is no longer reliable, and the grey whales are being forced to turn elsewhere for food.
Scientists have yet to determine just how much harder the grey whales are working to subsist, but the signs of emaciation are clear, according to Swartz.
Susan Moore, a colleague of Swartz at a research centre in Seattle, calls grey whales “sentinels of the sea” because the creatures are sampling and responding to the marine environment from Mexico up to Alaska, and like walruses and polar bears, are early indicators of ecological crisis.
But grey whales have patrolled the oceans for 30 million years, and have survived two ice ages. With the seas changing Swartz hopes the mammals can adapt.
He noted that the species was first named “robustus” in the 17th century after the discovery of a massive jawbone fossil.
“These whales are pretty hardy beasts,” said Swartz. “But they are having a tough go right now.”