FINAL Gray Whale Migration Update: May 17, 2000
Latest Highlights from the Gray Whale Observation Posts
Gray whales are still plowing north, but in smaller numbers, reaching as far Kuskokwim Bay (59.67N, 162.33W). The American Cetacean Society census taken at Long Point (33.74.N, -118.39W) ended on May 15 with lower numbers than in 1999. The northbound total as of May 14 was 1039 gray whales, including 19 cow/calf pairs. Unless lots of cow/calf pairs swam past the census point on May 15, this count is down from the 34 cow/calf pairs in 1998/99 and the 174 cow/calves in 1997/98. Total northbound numbers will be lower than last year, when 1383 northbound grays were counted. Why are whale numbers down? Susan Payne offers some ideas later in this Update.
For more sighting stories from the migration trail, including orca sightings, where to see data from the spring migration on the Oregon Coast, and details about the autopsy of a stranded gray whale, see Susan's full report:
Why So Many Strandings?
"I do not yet have the official numbers from the 1999 stranding report being compiled by the National Marine Mammal Laboratory, but from the news it appears that unusually high numbers of strandings happened in both years, and that some of these animals have been emaciated. This report from the Oregonian, and other reports point to food limitations in the Bering Sea. Environmental changes could be the cause. Another possibility is depletion of prey items by a large gray whale population.
Dr. Donald Schell is Director of the Institute of Marine Science at the University of Alaska, Fairbanks. Dr. Schell did a recent study that indicates environmental changes in the Bering Sea ecosystem have taken place. Dr. Schell spoke at Whale Fest Kodiak about his work. His topic was "Using Bowhead whales as indicators of environmental change in the Bering Sea" .
Dr. Schell looks at the atomic composition along the length of the bowhead whale's baleen. He compares the ratio of Carbon 13 to the more abundant Carbon 12 isotope. The isotope ratios measure what's accumulated in the keratin being deposited on the baleen, assimilated in the bowhead's food--primarily euphausiids and large calanoid copepods. Not only can Dr. Schell tell the whale's age with this technique, but also how productive the ocean has been over the whale's lifetime. From 1947 to 1997, Dr. Schell sees in these baleen readings that ocean productivity in the Bering Sea (the bowheads' winter feeding grounds) has fallen to its lowest point in 50 years. The latest samples, from 1994 through 1997, suggest that ocean productivity has decreased 35 to 40 percent since its peak around 1965. Dr Schell explained that "a 40 percent decline in the primary production of the ecosystem is going to have profound effects on the top consumers."
An adequate food supply in the Bering and Chukchi Seas is important to the gray whale because it is widely believed that most whales do not appear to eat significant amounts of food during either their southbound or northbound migrations. It has been estimated that the whales gain 16-30% of their body weight while on their northern feeding grounds, and this reserve must sustain them during both legs of their migration. In the three years that I have contributed to Journey North reports, we have consistently had reports of feeding whales along the migration route. These feeding whales included both migrating whales and seasonal residents. For the first time in peoples' memories here in Kodiak, more gray whales are staying year round in the Narrow Cape area. We will have to see if this use continues in the future, but it may be another sign that the Bering Sea is no longer an optimum feeding area, and the gray whale must find food resources in other places.
What do you think this would mean for the migration? For the whale population? Time will tell.
Orcas in the Arctic
Journey North received a letter this week from Larry Dickerson in the Arctic. Pull out a map and see if you can locate Larry's site from the description he wrote. Here's what Larry told us about his work and gray whale sightings in the far north:
Where's the Ice?
Even if some of the news seems grim, we can still celebrate the numbers of whales that are still plowing north, or happily feeding in the icy seas. You might want to see for yourself how far the whales can go this week in their Arctic feeding grounds. See:
Fill in the Blanks!
Answer for Challenge Question #19
"It is uncommon to see such a large group of transient orcas unless they have been feeding on a gray whale."
Answer for Challenge Question #20
"Of the 1011 Northbound gray whales counted by the ACS Census, the percentage of cow/calf pairs is 1.58%."
Answer for Challenge Question #21
"More than 500 northbound whales were sighted on these two April dates: 18 and 26."
Have a Whale of a Summer!
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