SEATTLE - When a whale eats a salmon, where does the salmon come from? Finding out the answer can tell scientists which stocks are the most important for maintaining and even growing the population of local Orcas that have been listed as endangered since 2005.
These so called "killer whales" are members of J, K, and L pods that spend much of their time in the waters of Washington and southern British Columbia. It's not unusual to see them in Puget Sound, but they spend much of the summer in the San Juan Islands.
Unlike transient Orcas, which eat other marine mammals, the Southern Residents dine almost exclusively on fish. And the fish at the top of their menu is the King, or Chinook Salmon...and it turns out most of those, some 90 percent come from the Fraser River in British Columbia.
The whales are showing a bit of a comeback with some recent births, but their numbers are still fewer than 90 animals. Food stocks and pressure on Chinook Salmon stocks because of things like pollution and development among the reasons why, in 2005, the National Marine Fisheries Service pushed for their inclusion on the Endangered Species List.
But Dr. Brad Hanson, of NOAA's National Marine Fisheries Service says 90 percent of the salmon the Southern Residents are eating are coming from the Fraser River and its tributaries, not from rivers south in the U.S.
He reached that conclusion by analyzing the genetic DNA signature from scales taken with nets right after an Orca kill, looking at other salmon remains, and analyzing whale poop.
Using several laboratories, the genetic samples were then checked against a database of fish known to spawn in the Fraser and other Northwest rivers. Scientists can get very specific because after salmon hatch, they head to sea and then return to spawn in the same place where they started and that gives an individual group of fish a distinct genetic signatures.
Hanson says at different times of the year the Orcas will dine on Chum, and more study needs to be done. But so far he says the evidence strongly points to the Fraser. Why the Fraser salmon rather than other? Hanson thinks that may be because there are simply more Fraser River Chinook around, and therefore more likely to become a meal when they're running.
But Hanson thinks it's possible the whales are being selective, picking out the fatter Fraser Chinook because they can contain far more calories than a Sockeye salmon that the whales are also known to eat.
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