Migrating Gray Whales Thin in 2007
Are Climate Change, El Nino or Ecosystem Overuse Responsible?
Jul 17, 2007
Large numbers of very underweight gray whales (Eschrichtius robustus), were seen this year during their migration north, less than 10 years after losing nearly a third of their population to starvation. Changes in their feeding grounds in the Bering Sea are likely the main culprit. Warmer sea temperatures have changed the ocean environment enough to alter some aspects of the ecosystem. This may be a natural result of an El Nino event or part of the predicted long term global warming. Overfishing appears to have contributed to the problem as well.
Grey Whale Migration and Starvation
Each spring gray whales migrate from their winter calving grounds in Baja California to their summer feeding grounds in the Bering Sea. During migration and calving the animals do not feed regularly, depending on a summer of heavy foraging to maintain their weight. Lack of food on the primary feeding grounds is clearly a problem. In 1999-2000 a loss of 33% of the population of gray whales occurred as a result of starvation. This year only 10% appear to be underweight and the death rate is not yet as high.
El Nino and Climate Change as Factors
The reasons for the decrease in prey in the Arctic are not completely understood but there has been a series of El Nino Southern Oscillation (ENSO) events in the last few decades. Food sources for all of the eastern and central Pacific Ocean are affected by these events, shifting fish further north. In the 1980s the Chirikov Basin was a primary gray whale feeding area with plenty of the amphipods that form the cetaceans’ major food source. The amphipods feed on algae dropping from the sea ice or carried by ocean currents. Since the late 1970s the Bering Sea has become warmer with less ice cover. Decline in sea ice and changing currents may be reducing algae levels and temperate fish migrating north on the warm El Nino waters may be impacting the amphipods directly. If a predicted change to a series of La Nina events occurs over the next few years, this one piece of the puzzle may be made clearer.
Overfishing
Overfishing has been implicated in the decline of other Bering Sea marine mammals. The area was heavily exploited from the 40s to the 70s, changing the ecology of the area and greatly decreasing biodiversity. How those changes have affected the amphipod and algae of the area is not well studied but changes to fish populations often result in changes to invertebrate and plant species.
Climate change has become the scapegoat whenever there are environmental problems in the world today. But there is a risk of ignoring other important issues by focusing solely on global warming as the source of all ecological troubles. Preventing any more ecosystems from being altered dramatically by exploitation remains an equally important task.
