Tag Archives: Predators

Finding answers to complex orca-salmon connection

The connection seems obvious until you look into the complexities:

  1. Puget Sound chinook salmon are listed as a “threatened” species.
  2. Southern Resident killer whales, which frequent Puget Sound, are listed as “endangered.”
  3. Southern Resident killer whales eat primarily chinook salmon.

Therefore … isn’t it obvious that the shortage of Puget Sound chinook has had a major impact on the whales?

Once you begin to challenge the assumptions — as a seven-member scientific panel has done — a more complex picture emerges. It is not easy to sort out predator-prey interactions, especially considering that the prey may include hundreds of individual salmon stocks, some of which are doing quite well.

The independent panel (PDF 144 kb), made up of U.S. and Canadian scientists, tackled the question of whether cutbacks or elimination of salmon fishing could help rebuild the killer whale population at a faster rate. The panel’s preliminary conclusion is that reducing fisheries could have a slight benefit, but only if certain assumptions hold true.

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Transient orcas may be leaving uneaten food behind

UPDATE, October 27, 2010

In a new development, resident killer whales have been seen toying with harbor porpoises, according to a story by reporter Larry Pynn, who writes about the phenomenon earlier this month in the Vancouver Sun.

He included comments from Joe Gaydos, who was my source on this blog post. He also quoted John Ford, a researcher with the Canadian Department of Fisheries and Oceans, who said females may be treating them like their own offspring:

“It could be a maternal-driven behavior that is misdirected towards another species. These animals (porpoises) are often sort of carried about on their backs or heads, pushed around. It’s almost like a behavior you’d see with a distressed or dead calf of a killer whale. We’ve seen a still-born calf pushed along or carried along by the mother.”

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We normally think of predator-prey relationships as being highly efficient systems with little waste. But Puget Sound researchers are finding that some transient killer whales seem to be killing sea lions for no apparent reason.

I’ve always thought that predators kill and eat what they need for survival, thus holding in check the prey population. Predators would never kill more than they need, I assumed, because they would risk eventually wiping out their food source.

Well, it’s time to rethink how some predators think.

Joe Gaydos of the SeaDoc Society tells me that transient killer whales, which eat marine mammals, have apparently killed three Steller sea lions and one California sea lion within a month’s time in Puget Sound and the San Juan Islands.

Examinations of the animals show that they died from blunt trauma, including broken chest bones and abdominal cavities filled with blood. No gunshot wounds or other complicating factors were seen.

Joe told me that boat strikes can cause similar injuries, but it seems unlikely that this many boat injuries could occur in the same precise way with no other injuries being observed. Instead, it appears likely that transient orcas killed them without even taking a bite.

“Cold-blooded killers,” I suggested. I should have asked him about a recent incident in which a group of transients attacked a much-loved gray whale near Whidbey Island before letting it go.
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Gray whales survive rare encounter with orcas

Three gray whales traveling together south of Camano Island in Puget Sound must have sensed mortal danger when a group of transient killer whales approached them this afternoon.

Transient orcas are the kind that eat marine mammals. Groups of transients are known to kill gray whales in other places, including Alaska’s Aleutian Islands.

But encounters between transients and gray whales in Puget Sound are basically unknown, even though both orcas and grays are frequently spotted in these parts.

Erick Peirson, skipper aboard the 41-foot Olympus out of Port Townsend, was giving a whale-watching tour for about 30 passengers today. He had gone out to see if he could locate two adult gray whales traveling with a younger gray. Instead, the crew spotted the transients — one male, two females and a juvenile. Passengers were watching them when an observer shouted in excitement.

The male orca had completed a long dive underwater, coming up right alongside the grays, Peirson said.

“I saw a lot of splashing and churning of the water,” he said. “The male killer whale’s fin was slicing into a turn. In the middle was a gray whale fluke.”

It was clear, he said, that the two adult gray whales had quickly positioned themselves in a defensive posture, one on each side of the younger gray whale.

“The male killer whale rubbed up alongside the biggest gray whale,” Peirson said. “The gray whales were logging at the surface, just sitting right there. We thought the killer whales would go in for the kill at that point.”

Instead, the orcas broke away. “We next saw the killer whales in the distance heading to the north.”

Perhaps the gray whales heaved a sigh of relief, blowing a huge mist that only gray whales can blow. They stayed another five minutes, logging on the surface in that defense posture, Peirson said.

While he has seen transients attack seals, he has never seen an encounter like this in Puget Sound.

“It was a bit of a rush, not something you see every day,” he said. “Usually with transients, when an attack happens, it is over very quickly. We saw no blood at the surface. Given that it was a single path and circling around, I assume the killer whales were testing the waters, a show of strength.”

For a slideshow put together by Patrick Downs, go to Flickr. I guess the encounter happened so fast that he did not get the killer whale and gray whale in the same frame, but you may notice the defensive posture described by Erick Peirson.

As I mentioned, groups of transient killer whales have been observed attacking and eating gray whales in the Aleutian Islands. (See the research report by Craig Matkin, et al., PDF 1.1 mb) But neither Peirson nor Howard Garrett of Orca Network, who records thousands of observations every year, has ever heard of this kind of encounter in Puget Sound.

As unusual as this is, I would like to hear from anyone who has experienced any encounters, however brief, between killer whales and gray whales.

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