Tuesday, 3 September 2013

Migrating whales provide entertainment for dolphins - Photo

September 2013. In the photo, a group of long-beaked common dolphins are hitching a free ride on the bow wave of a migrating gray whale. Taken near Catalina Island off the coast of Southern California, the photo was shot from about 600 feet by scientists with the Cetacean Health and Life History Program at the US National Oceanic and Atmospheric Administration's (NOAA) Southwest Fisheries Science Center.

Every year, almost the entire population of eastern North Pacific gray whales migrates from their feeding grounds in the Arctic down to their breeding and calving grounds off the coast of Baja California, Mexico. And most years, NOAA scientists survey and photograph the whales from the air. By analysing the high-resolution photos, scientists can tell how well-nourished the animals are, how many females are pregnant, and how many new calves are born.

Health check
One reason for doing this is to keep an eye on the health of the gray whale population. But in addition to that, the photographic study is an indirect way of monitoring the Arctic ecosystem. The primary feeding grounds for the eastern north Pacific population of gray whales are in the Arctic. The rest of the year they fast or eat very little. So their physical condition during migration reflects conditions in their feeding grounds in the Arctic.

Climate change
"We know the Arctic is changing, and changing pretty rapidly," said Wayne Perryman, a biologist with NOAA's Cetacean Health and Life History Program. "We want to know how this is impacting the gray whale population."

For example, many of the species that gray whales feed on are shifting northward as the Arctic warms. This means that gray whales have to migrate further north to feed. For pregnant females, who by the time they arrive in the Arctic have been fasting for many months, this extra travel may be energetically taxing. One of the things that Perryman and his colleagues are studying is the relationship between the length of the migration and the rate of successful pregnancies.

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