7 orcas, regular visitors to Sound, likely dead

Seven orcas that regularly visit Puget Sound are feared dead — if so, it would be the biggest die-off in about 10 years — and some experts say dwindling populations of chinook salmon are at least partly to blame.

Among the orcas missing since November are the oldest and youngest members of the group, as well as two females in their peak productive years.

"I was shocked," said David Dicks, executive director of the Puget Sound Partnership, scheduled to issue on Nov. 6 its draft plan for preserving and protecting Puget Sound.

The news of the orcas' decline adds to the urgency of the mission, Dicks said. "Time is not on our side."

The orcas were listed as an endangered species in November 2005 and largely depend on Puget Sound chinook — listed as a threatened species nearly a decade ago — for food.

To some, the plight of the dual icons of Puget Sound indicates not only two species in trouble, but an ecosystem in decline.

"Orcas don't exist in a cafeteria somewhere; they depend on the overall bounty of the natural world," said Howard Garrett of Orca Network, a Whidbey Island-based advocacy group. "Protecting Puget Sound equals saving salmon, which equals saving orcas."

If the seven orcas are indeed dead, the southern resident population that regularly visits the Sound is now at 83 animals, the fewest since 2003, and down from a recent high of 97 in 1996.

"We haven't seen anything like this in about 10 years; it's higher than the normal number of mortalities," said Brad Hanson, a wildlife biologist with the National Marine Fisheries Service in Seattle. "It's a combination of not only young animals but these animals in other age classes dying. It's unclear exactly what's going on."

One contributing factor, he said, is food. Studies have shown a correlation between chinook and orca populations, said Hanson, who with other researchers has studied the orcas' diet for a decade. Orcas have a strong preference for chinook, the largest and most nutritious salmon in Puget Sound.

The chinook population is depressed. Only 22 of at least 37 historic populations of chinook survive, and the remaining chinook are at only 10 percent or less of their historic numbers.

Contaminants in the food chain also affect the quality of what the orca are eating. And vessel noise makes it harder for orcas to find food. Orcas locate their prey by echolocation, a form of sonar. Researchers believe the noise of boats is one of the factors putting orca survival at risk.

One of the orcas last seen this summer was emaciated. Hanson said tissue samples obtained by researchers may determine if it starved.

An inadequate diet also may have contributed to a depressed immune system that made her more vulnerable to disease.

"People say they could eat hake, or they could eat cake," said Ken Balcomb of the Friday Harbor-based Center for Whale Research, which has been tracking orca populations in Puget Sound since 1976. "It's just arrogance, or actually ignorance. If chinook aren't doing well, the whales aren't, either."

Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com