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.”
—–
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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