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Photo by Alan Corbett
A transient orca pursues a harbor porpoise Sunday in Fritz Cove. This whale is one of a pod of transient orcas which has been spotted hunting prey north of Juneau this week. Scientists say they may not be in the area for long.

Attack of the passing predator

Feeding habits of transient orca pod observed in Juneau waters this week

Posted: August 9, 2012 - 11:00pm
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A pair of transient orcas pursue a harbor porpoise Sunday in Fritz Cove. This pod of transient orcas has been spotted hunting prey north of Juneau this week. Scientists say they may not be in the area for long.  Photo by Alan Corbett
Photo by Alan Corbett
A pair of transient orcas pursue a harbor porpoise Sunday in Fritz Cove. This pod of transient orcas has been spotted hunting prey north of Juneau this week. Scientists say they may not be in the area for long.

Residents of Fritz Cove got quite the show Sunday as a pod of transient killer whales pursued and killed a harbor porpoise.

Then, yesterday, near the Shrine of Saint Therese, tourists and locals in the area witnessed what may have been the same pod chasing a bull sea lion.

Alan Corbett, a local Juneau resident, photographed the action in Fritz Cove. He also witnessed, but did not photograph, the action near the Shrine.

His pictures show the hulking black body of an orca leaping skyward in pursuit of the smaller harbor porpoise.

The scene, he said, was a bit grim, as the harsh reality of transient killer whale life unfolded before him; they were, after all, living up to their common moniker.

“I was shocked,” he said. “I’ve lived in Juneau for about eight years ... and have done a lot of wildlife photography, but I’ve never seen this.”

It’s fair to say few have. But his photography skills kicked in and the shutter began to snap.

The images are captivating, even for people like Marilyn Dahlheim, a biologist with the National Marine Mammal Laboratory, a subsidiary of the National Oceanic and Atmospheric Administration, who has spent more than a decade studying orcas. She said photographs like the ones Corbett made are rare, but the behavior of the whales is absolutely not.

“These are expert hunters,” she said. “It’s not unusual for them to take a porpoise. (In fact,) we see it quite a bit.”

The diet of the transient orca varies, she said. These whales have been observed preying on Dall’s porpoises, Pacific white-sided dolphins, minke whales, Steller sea lions, harbor seals, seabirds, moose, deer and, of course, harbor porpoises.

“A couple years ago, (a transient orca pod) took a cow moose and her calf near Gustavus,” Dahlheim said. “They also took a bunch of Pacific white-sided dolphins just off the pier in Petersburg.”

Other potential prey species include humpback whales, elephant seals and sea otters, according to a paper Dahlheim published recently with fellow researcher Paula A. White titled “Ecological aspects of transient killer whales Orcinus orca as predators in southeastern Alaska.”

John Moran, a research fisheries biologist for the National Marine Fisheries Service at the NOAA Auke Bay Laboratories, said the Auke Bay and Fritz Cove areas are popular feeding places for the transients.

“Harbor seals, harbor porpoise, sea lions and even a minke whale have been taken there,” he said in an email Thursday. “Dall’s porpoise are also on the menu, but they seem to stay in more open water where they can use their speed to escape.”

It’s unlikely the transient whales will hang around long, however.

These animals, known as the West Coast Transient Pod by scientists, range from British Columbia and Washington, up the coast to Southeast. It’s fair to say their home range is extensive, Dahlheim said; 90 percent of the animals seen in Southeast are also seen in Washington and British Columbia.

The reason for this large range is necessary.

“They hang out, but not for long because their prey gets leery,” Dahlheim said. “They move through an area rapidly, travelling between 4-6 knots per day.”

Sometimes, she said, they will hang around, if there’s food. There was one time, for instance, she remembers them hanging around the backside of Douglas Island, eating sea lions.

“Mostly, it’s the females that lead the attack, with the juveniles right in there, as well. The males, like big ol’ male lions, often hang back,” she said. “However, they do share food.”

When Dahlheim first began studying these whales, she said they thought each pod was specialized at killing a specific type of prey. This, they have found, is not true. Instead, transient orcas have a specific way to kill each of their favorite types of prey.

“A sea lion, (for instance,) could do a lot of damage to an orca,” Dahlheim said. “Instead of hitting it with their nose, they hit the sea lions with their tail in an effort to injure it. With the porpoises, they just kind of get behind it and slurp it up ... Any top predator has the ability to learn pretty quick.”

Resident orcas can also be found in Juneau waters, but those pods only eat fish and can co-exist with transients, scientists believe, without conflict.

Dahlheim is currently working on cataloging transient orcas in the region through identification of individuals.

“What we do is take a picture of the left side of the animal. We try to get a good image of the saddle (the identifying patch behind the dorsal fin),” she said. “Then we look at whether or not there’s scratches on it and we look at the shape (and condition) of the dorsal fin.”

These markings, along with satellite tags, help them track individuals and pods as they migrate within their home ranges and can offer insight on how long an animal stays in an area.

What they have found, she said, is that the West Coast Transients have restricted movements.

“They don’t go too far north, or west,” Dahlheim said. “Once you get into Prince William Sound, you’ll find an entirely different group of transient orcas. Those are called the Gulf of Alaska Transients.”

North of Juneau this week, gasps of awe were punctuated by the splashing of large mammals. Cameras clicked. Jaws likely dropped.

The whales, Corbett said, echoed Dahlheim’s findings in real time.

“The pods seemed to break into three groups,” Corbett said. “A male and female worked further out from shore. One female had a juvenile with her.”

He said it was clear they knew what they were doing and knew exactly how to attack the porpoise. When it came to the sea lion, he said their approach was totally different.

“That seem to be a training kill,” he said. “They obviously changed tactics; they were doing low breaches and hitting the sea lion.”

At the time Corbett was leading a whale watching tour.

“To witness the ferocity and speed of the orca ... and to see them doing what they do ... It was just amazing,” he said.

 

• Contact Outdoors editor Abby Lowell at abby.lowell@juneauempire.com.

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