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       A statement from the Center for Whale Research in Washington state says a 47-year-old female killer whale identified as L47, seen in 2015 with her son L115, has not been seen for nearly seven months and is likely dead.

       HO/The Canadian Press

       Scientists are reporting another challenge to the population of critically endangered southern resident killer whales in the waters off British Columbia, Washington State and Oregon.

       A statement from the Center for Whale Research in Friday Harbor, Wash., says a 47-year-old female identified as L47 has not been seen for nearly seven months and is likely dead.

       The centre says its teams have spotted the female’s three surviving offspring and their two calves several times since she was last seen off B.C.’s Salt Spring Island in February, but she was not with them.

       Her likely death and the confirmed death in July of a 35-year-old male orca from a different pod drop the total number of exclusively salmon-eating, southern resident orcas to 73.

       Older, post-reproductive females hold a key, matriarch-like role in southern resident pods, especially when food is scarce, and the centre says the loss of this female’s leadership could have severe consequences.

       It says the risk of death for her children and their offspring over the next two years is three to six times higher, and it could increase if salmon populations continue to dwindle.

       Endangered southern residents travel in three separate pods: K, J and L.

       L47, who was also known to researchers as Marina, was a matriarch of L pod, which now has about 32 members.

       She has had seven calves and they survived long enough to be given alphanumeric designations, the most of any southern resident.

       The centre says its studies show matriarchs support the survival of the pod by acting as “repositories for ecological knowledge,” guiding their groups to salmon foraging grounds, and that their knowledge is especially important during years when salmon returns are low.

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       It says older reproductive females can also fill this role, raising the potential that L47’s leadership could pass to either of her daughters or any other older female within the pod.

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