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Gray Whales and Changing Sea Ice
What Scientists Think

Since 1978, scientists have used satellites to track sea ice and other factors in the Arctic. This long-term data has let them observe dramatic changes they could not have seen in a short time period. Here are some of their findings and theories.


Yearly Sea Ice Animation
Click for large map.
Photo: Ron Morris
Arctic Sea Ice is Melting!
  • In the past few years, Arctic sea ice has melted unusually early in the spring. In fact, in the 2004-2005 winter season, it began to melt earlier than in any other winter on record. In the gray whale's feeding and breeding grounds in the Bering sea, it's melting about three weeks earlier than in 1997.
  • Arctic ice coverage and thickness has dropped steadily during the last few decades. Now the minimum cover is the lowest ever measured since sea ice cover records were kept.
  • During the past few decades, annual average temperatures in the Arctic have increased at almost twice the rate as in the rest of the world.

Why It's Melting
  • Sea ice is light-colored, so it reflects most of the sun's energy (heat) back into space. But as the sea ice melts, the darker water absorbs much of this energy. This warming water melts the ice even faster!
  • Scientists say that global climate change is the main cause of the warming of the Bering Sea. (Another is weaker cold north winds that blow across the sea.)
  • Human activity, such as burning fossil fuels, is a key cause of global warming. It releases tons of carbon dioxide and other "greenhouse gases" into the air. These cause the Earth to trap more of the sun's warmth than it otherwise would.

How Could it Affect Gray Whales?
The north Bering Sea is one of the world's richest feeding grounds for whales, walruses, and sea birds. Scientists only know some of the ways in which climate change affects marine life. After all, it's a complex system. Everything is linked to everything else! Here are some of their observations. What other ideas did you come up with?
    Click each photo to enlarge.

    A microscopic phytoplankton.

    An adult gray whale will swallow about 77 tons of food in the Arctic. That's a LOT of amphipods, which are only a few centimeters long!
  • Less food available — Microscopic sea plants called phytoplankton are the starting link in the Arctic sea food chain. Each spring as sunlight hours increase, they start to make food and grow under the ice. They grow so fast that they crowd each other out by June. As they suffocate and die, they fall to the muddy bottom. This creates a nutrient-rich food layer. Bottom-dwelling animals such as amphipods — the main food for gray whales — feed on that layer. But as ice melts earlier and water warms, the phytoplankton's life cycle is disrupted. The result? Less food for every animal in the food chain!

  • Food competition Near-freezing water in the northern Bering Sea once kept bottom-feeding fish like halibut and flounder farther south in warmer waters. But as sea floor temperatures have risen, the fish have moved farther north. There they compete for food with larger animals, such as walrus, sea ducks, and whales.
  • Whales moving north Researchers say that gray whales are adjusting to the changes by heading further north. There they feed in colder waters of the Chukchi Sea. But those shallow waters only go so far! Once whales get to the deep waters off the continental shelf, they won't be able to find food. (Other animals, such as bearded seals, may not be able to adjust enough to survive.)

    As the gray whales shift northward, they move near the territory of the bowhead whale, which feeds offshore. Alaskan natives hunt and eat the bowhead. They are concerned that the more aggressive gray whale may interfere with the quieter bowhead. Hunters are noticing that many gray whales are sticking around all winter rather than making the journey south!

Digging Deeper: You Be the Judge!
Read these articles. As you do, highlight, underline, or keep lists of the following:
  1. evidence of changes in sea ice and climate
  2. ideas about why these changes are happening (use one color for facts and another for theories/opinions)
  3. ideas about how these changes affect gray whales (use one color for facts and another for theories/opinions)
  4. Your opinion on what you think we could do to slow down these changes.

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