NOAA finds orcas eat specific salmon

Published on Thu, Jun 10, 2010
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New advances in genetic testing have allowed scientists to determine the specific origin of Chinook salmon that were consumed by  killer whales in the inland waters of Washington and British Columbia, according to new research by NOAA scientists and others. These findings will play a significant role in assisting the recovery of this group of endangered whales.

“Our findings identified specific Chinook stocks from Canada’s Fraser River that fish managers need to pay particular attention to because these killer whales are so dependent on them,” said Dr. Brad Hanson, lead author of the study and a marine mammal scientist with NOAA’s Northwest Fisheries Science Center in Seattle. This group of killer whales, known to scientists as the Southern Resident population, is protected under the U.S. Endangered Species Act and Canada’s Species at Risk Act.

Both governments identified lack of food as a risk factor that could interfere with the recovery of these killer whales.

Southern resident killer whales spend their time in the inland waters of Washington and British Columbia from late spring to early fall before swimming to the Pacific Ocean for the winter months.

Scientists estimated that the vast majority of the Chinook the whales ate – as much as 90 percent — was from the Fraser River. The whales ate mostly salmon from the Upper Fraser in June, the Middle Fraser in July, and from the South Thompson and Lower Fraser in August and September. In general, only a small fraction of the Chinook salmon samples came from Puget Sound rivers. 

Salmon return to the same stream or branch of a river where they had hatched to spawn. Therefore, salmon from a particular stream become a genetically distinct population from those that spawn in other streams or river systems. Each population returns at a slightly different time of year.

The whales ate the salmon as the fish returned to the Fraser River to spawn.

The four-year study involved collecting fish tissue and scales, as well as whale feces, while the killer whales fed during the summer months. In the laboratory, scientists used a relatively new molecular genetic tool to identify which fish species were eaten and, more specifically, where they came from.

 “This study not only confirmed previous research that suggested these whales eat mostly Chinook salmon, it also allowed us to identify the specific genetic groups, and therefore the specific areas from within the river system, from which these salmon came,” said Hanson. This gives managers more information with which to make decisions about conservation measures to ensure survival of these salmon stocks, which in turn are vital to the survival of the killer whales.

For more information on southern resident killer whale recovery, visit:  www.nwr.noaa.gov.