Oh Deer! A rare meal for mammal-hunting killer whales?

By The Marine Detective on March 2, 2013

This is not a tall tale. If anything it is a short tail as in – deer tail.

First an orientation on Killer Whale (Orcinus orca) diet and how prey specialization has shaped distinct cultures over great expanses of time.

There are different “ecotypes” of Killer Whales that do not mate with one another because what works, for example, to chase salmon does not work to stalk seals. They have distinct cultures and distinct languages. [Click here for detail on the different ecotypes of Killer Whales off British Columbia, Canada.]

The fish-eating Killer Whale ecotypes in the NE Pacific Ocean (Northern and Southern “Residents” and “Offshores”) can afford to be extremely vocal because fish species often have poor hearing.

However, the mammal-hunting ecotype (“Bigg’s Killer Whales“, previously know as “Transients”) must generally live a life of stealth and unpredictability in order to successfully hunt their prey. To be vocal or be really surface active, when they are hungry, would have a high cost. It would be like ringing a dinner bell announcing “Hello, we’re here to eat you!”

In fact, recent research supports that the NE Pacific mammal-hunters diverged from the other ecotypes of Killer Whales some 700,000 years ago and puts forward that they should be recognized as a distinct species (Morin et al 2010).

Pacific Harbour Seals are predictable in where they haul out and they do not have defences like speed and sharp teeth. Therefore, it is not surprising that off the coast of British Columbia, Pacific Harbour Seals are documented to be the prey item of choice for the mammal-hunting Killer Whales (see graph above).

Far less commonly, these Killer Whales have also been documented to feed on River Otters, Northern Elephant Seals, Sea Otters and – VERY, VERY occasionally – a terrestrial mammal like deer.

Please see below for images of a deer carcass found underwater by fellow divers Gary Marcuse, Rob Roy and Mike Juren in May of 2012. There is no way of  knowing with certainty if that this deer was attacked by Killer Whales but it is plausible. Deer swim from island to island and are even more defenceless than a seal if they have the bad luck that stealthy mammal-eating Killer Whales find them.

Killer Whales are big dolphins – smart and social and even though they tend to be very conservative, doing what has worked for their kind for 100,000s of years, they also play – learning from interacting with their environment. I have reflected on this previously in my blog where I observed them mouthing and hitting diving birds. (Read “Fins vs. Feathers” by clicking here).

Deer could never make up a significant part of the diet of Bigg’s Killer Whales but they would learn from such an attack. If this deer did indeed meet its end in the mouth of a mammal-hunting Killer Whale, I would not be surprised if it was a juvenile mammal-hunting Killer Whale who undertook the “interaction”.

To share the expertise of Killer Whale researchers supreme, Dr. John Ford ad Graeme Ellis, from their 1999 publication “Transients -Mammal-Hunting Killer Whales” (and note that an attack on a moose has only ever been documented ONCE):  

“Although the primary prey of transient [now Bigg’s] killer whales are marine mammals, the whales’ interest extends to other warm-blooded animals, including marine birds .  . . and even terrestrial mammals. Our first record of land mammal predation dates from June 1961, when Canadian fishery officers observed killer whales feeding on a deer carcass in Jackson Pass on the central coast of British Columbia. Deer frequently swim from island to island along the inside passages, and it is probable that this one fell victim to a foraging group of transients. More recently, off the east coast of Vancouver Island, several killer whales were observed circling a small rock on which two deer had taken refuge. On another occasion, a lighthouse keeper assisted an exhausted deer out of the water as it was being pursued by killer whales. In these case, there has been no photographic confirmation that transients were involved, but it seems almost certainly the case.

Other land mammals are also of interest . .  on occasion . . . a killer whale was observed to surge part way onto shore in an apparent attempt to attack a dog that was barking loudly at the passing group.  . . .

One of the most surprising attacks on a terrestrial mammal took place in 1993 in Icy Strait, south-eastern Alaska. Two fishermen observed a group of three or four killer whales attack and kill one of a pair of moose that were swimming across the channel. The other moose managed to escape the attack but later became entangled in a kelp bed and drowned.”

So am I worried, as a very avid and very mammalian scuba diver, that I have the same chances of being attacked as a deer swimming between islands? Absolutely not. There has never been a case of Killer Whales in the wild killing a human.

To again relate John Ford and Graeme Ellis’ expertise:

“Divers in this region typically wear thick suits made of neoprene rubber, which contains acoustically reflective nitrogen bubbles. Thus, if a transient [Bigg’s killer whale] tries to inspect a diver with echolocation, its unlikely to get a typical mammalian echo. Although scuba divers may not appear appetizing to [them], this may not be the case for swimmers, so it is advisable to leave the water should transients [Bigg’s] appear in the vicinity.” 

I also love the perspective of a fellow diver and friend, Peter Mieras, who states that Killer Whales “are too smart to go after junk food in wrappers.”

Oh deer!

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Sources:

• Barrett-Lennad L. 2005. “The Complicated Predator” – presentation
• Ford, J.K.B. et al. 1998. Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in coastal British Columbia and adjacent waters. Canadian Journal of Zoology 76(8): 1456-1471.
• Ford, J.K.B., and Ellis, G.M. 1999. Transients: Mammal-Hunting Killer Whales of British Columbia, Washington, and Southeastern Alaska. UBC Press, Vancouver, and U. of Washington Press, Seattle. 96 pp
• Ford, J.K.B., Ellis, G.M., Matkin, D.R., Balcomb, K.C., Briggs, D., and Morton, A.B. 2005.Killer whale attacks on minke whales: prey capture and antipredator tactics. Marine Mammal Science 21:603-618.
• Kuker, K., and Barrett-Lennard L. 2010. A re-evaluation of the role of killer whales Orcinus orca in a population decline of sea otters Enhydra lutris in the Aleutian Islands and a review of alternative hypotheses. Mammal Rev.
• Morin PA, Archer FI, Foote AD, Vilstrup J, Allen EE, Wade P, Durban J, Parsons K, Pitman R, Li L, Bouffard P, Abel Nielsen SC, Rasmussen M, Willerslev E, Gilbert MTP, Harkins T 2010. Complete mitochondrial genome phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species. Genome Res, doi:10.1101/gr.102954.109
• “Recovery Strategy for the Transient Killer Whale (Orcinus orca) in Canada [Final Version]” (2007-12-13)