(CN) – An endangered population of orca whales continued to decline this summer, with three presumed dead while the remaining 73 search the ocean for their main food source: dwindling numbers of Chinook salmon.
The Center for Whale Research, which has catalogued the family tree of Southern Resident killer whales since 1976 for the National Marine Fisheries Service, announced late Tuesday that three are missing and likely dead.
Southern Residents normally spend the summer in the salty inland waters near Seattle. They’re so ubiquitous in the Salish Sea that a whale watching industry was built on their daily appearances in the area. But this year, they’ve barely been seen in the core waters of their designated critical habitat. Instead, the collapse of mainstay populations of Chinook salmon has sent them chasing fish along the Pacific Coast from Canada to California.
Malnourishment and stress are the likely cause of death for the three whales, according to Michael Weiss, biologist with the Center for Whale Research. Their bodies have not been recovered – the norm for animals who sink to the bottom of the ocean when they die.
“They’re all kind of in a constant state of slight starvation,” Weiss said by phone. “When you’re not getting enough food, you’re more susceptible to injuries and infection. What probably happened is they just weren’t getting enough food for a while and caught some kind of bug and that led to them catching even less food and that led to them deteriorating even more than the rest of their family groups.”
Southern Resident killer whales live and travel in three extended families called pods, designated J, K and L. One whale from each pod is missing. Orca have human lifespans and can live to be 100. But these whales died young.
J17 was a matriarch of her pod at the age of 42. Three of her offspring survive: J53, J44 and J35, who carried her dead calf for 17 days last summer. Last seen May 31, aerial drone photos show J17’s physical deterioration.
Mother whales typically share food with their sons. Weiss said that while none of the surviving whales appear to be in bad shape, the center is keeping a close eye on J17’s son J44.
“The last time we saw them, no one looked too skinny,” Weiss said. “But there are a couple we worry about based on their relationship to the deceased, J17, especially because she was the grandmother, the matriarch of J pod. In particular we might worry about her son. We know that in the years following their mother’s death, males have an increased chance of death.”
Another missing whale, 28-year-old K25, should have been “in the prime of his life,” according to the center. Instead, he developed “peanut head” last winter – a syndrome where the normal fat deposits shrivel behind an orca’s head, revealing the base of their skull. Whales with peanut head typically don’t survive long. K25 has two living sisters, K20 and K27, as well as a brother K34.
And L84, a 29-year-old male, has not been seen all summer either in the Salish Sea or in surveys by the Canadian Department of Fisheries and Oceans along the west coast of Vancouver Island. He was the last living member of an 11-whale matriline.
“Three deaths in one year is on the high end, but it’s not completely unusual,” Weiss said. “It’s important to remember that in the 1990s, this population had nearly 100 members. So these deaths are not so much a shocking, unexpected blow as they are a part of a larger pattern of decline.”