Six orcas have apparently disappeared from the Southern Resident orca pods this year, dropping the population to 83, the lowest since 2003.

The Center for Whale Research and others are blaming marine pollution, depleted salmon runs, and acoustic impacts from dredging, seismic testing and military sonar for the decline in the population. The Southern Resident orcas are listed as endangered in Canada and the U.S.

“It’s a hard hit,” said Dave Ellifrit, senior staff assistant at the center.

The news comes amid dire reports in Canada and Washington state that depleted salmon runs are leading to the orcas’ starvation. And in Vancouver, B.C., the environmental advocacy group Ecojustice today sued Canada’s Department of Fisheries and Oceans, alleging the agency has failed to legally protect critical habitat of the endangered Southern Resident and threatened Northern Resident orcas.

The orca pods are called “residents” because they spend a majority of the year here, chasing the salmon runs.

Three Southern Resident orcas didn’t show up with their pods at the beginning of the season — K7, believed to be 98 years old and the oldest of all the orcas; J43, a calf born late last fall; and L101, a juvenile male that had been photographed in Monterey, Calif. Jan. 27.

By Sept. 30, when the Center for Whale Research concluded its annual survey of the Southern Resident population, three more were missing: L67, the 30-something mother of L101; J11, a female born in the early 1970s; and L21, a female born in 1950.

J11 has three healthy offspring, according to Ellifrit. But L67’s offspring haven’t fared as well. In addition to L101, L67 was the mother of Luna, the male orca that separated from the pod in Nootka Sound in 2002. Luna was killed by a boat propeller in 2006.

L67 appeared to be malnourished the last time center staff members saw her; she had “peanut head,” a term for a depressed area behind the blowhole that normally stores fat.

In addition, L111, a calf born in August to L47, is believed to have died. (Calves are not included in the population count until they survive a year). All told, L47’s last four calves have died, according to Ken Balcomb, executive director of the center.

The resident orcas have long been beleaguered. In the late 1800s and early 1900s, fishermen saw them as competition and shot them. Later, orcas were captured for marine parks.

Their population, believed to have once been in the 120s, plummeted to 71 by 1973. It rebounded to 99 in 1995, then plummeted to 79 six years later.

The population rebounded to 80 in 2002, 83 in 2003, 85 in 2004 and 89 in 2005, then seesawed around 88 since then. The local pods were declared endangered by the U.S. and Canada by 2005 and the National Oceanographic and Atmospheric Administration has been patrolling the area to enforce rules requiring boats to maintain a distance of 100 yards from the whales.

Howard Garrett, director of Orca Network, told the Victoria Times-Colonist in a story published earlier this week that Southern Resident orcas he’s observed are “looking sick.”

“There is usually a thick layer of blubber just behind the skull, and that seems to be the first place to be drawn from when they need to draw down blubber,” he told the Times-Colonist. “In some of them, there’s a dip right behind the blowhole and, when you see that, you know the whale has been hungry.”

An adult orca can eat four chinook salmon a day, Balcomb said. But the Puget Sound chinook salmon run is expected to be about 22,000 this year; that’s slim pickings when shared with commercial and recreational fishers. It’s also a far cry from the standard stock of 1 million salmon that Balcomb remembers in the 1970s.

Balcomb said the ups and downs of the orca population over the last 30 years parallels the ups and downs of the chinook salmon population. “If the chinook population doesn’t do well, the whale population doesn’t do well,” he said.

Balcomb suggested that a 10-year moratorium on salmon fishing would enable salmon populations to rebound. But even a suggestion of a moratorium by fisheries managers would be politically difficult, he said.

Regarding that Ecojustice lawsuit: Representatives of the organization said they and other plaintiffs are frustrated by the Canadian government’s failure to take steps under its Species at Risk Act to protect the orcas. The lawsuit claims that on Sept. 10, DFO declined to issue an order to “protect the orcas’ critical habitat from destruction.”

Ecojustice is joined in the lawsuit by the David Suzuki Foundation, Environmental Defence, Greenpeace Canada, the International Fund for Animal Welfare, the Raincoast Conservation Society and the Wilderness Committee.

“This is the first lawsuit ever of its kind in Canada,” Ecojustice staff lawyer Lara Tessaro said in a press release. “We hope to force the federal government to legally protect the critical habitat of endangered species, like the Southern Resident killer whales.”

Bill Wareham, senior marine conservation specialist at the David Suzuki Foundation, said Canada needs to legally protect areas that serve the orcas’ basic needs for food and rest.