Killer whales heading south

South Sound harbor seals can rest a little easier these days.

A pod of five transient killer whales that spent most of September in South Sound feeding on harbor seals was spotted Monday morning traveling south off the coast of northern California, according to marine mammal research biologists tracking their whereabouts.

The two adult females and three offspring left South Sound on Sept. 28 after first being seen here Aug. 31, based on reports to the nonprofit Orca Network.

In the past week, they traveled through the Strait of Juan de Fuca to the Washington coast, then made a beeline south, showing up near the Oregon-California border Sunday, said Brad Hanson, an ecologist at the Northwest Fisheries Science Center in Seattle.

The science center is a division of the National Oceanic and Atmospheric Administration.

The transient killer whales can typically travel 75 miles per day at an average speed slightly above three miles per hour, Hanson said.

“They didn’t stall out in any one particular place on the way south,” he said.

Hanson has fairly precise data on the five orcas’ location based on a satellite tag he and fellow marine mammal researcher Robin Baird of Cascadia Research Collective in Olympia placed on one of the adult orcas during a Sept. 20 encounter near Ketron Island.

The tag transmits signals 16 hours a day, giving researchers 10 to 16 locations every 24 hours beamed back to earth from orbiting satellites.

Orca researchers have been using the tags for a little more than a year to track several groups of transient killer whales in the marine waters from Alaska to California.

The nine days of data gathered in South Sound showed the five orcas repeatedly cruising most of the South Sound inlets and bays, much to the delight of waterfront residents and boaters.

“It’s hard to say how long the tag will transmit for,” Baird said. “The longest we’ve had one on a killer whale is 94 days.”

The South Sound visit was the longest by a group of transient orcas since 2005 when six orcas stayed in Hood Canal 18 weeks.

Adult orcas can weigh up to six tons and are the relative size of a bus. Sitting at the top of the marine food chain, they have no predators.

The transient orca population is distinct from the three pods of Puget Sound killer whales, which feed on salmon and other fish and are listed as a federally endangered species. The resident population was 85 in April 2009, according to the Center for Whale Research, a Friday Harbor-based whale research group.

Dwindling food supplies, chemical contamination, human disturbances and other factors have led to their decline, scientists have said.