Why are transient orcas attacking humpback calves in northwest waters?

Passengers sat aboard boats on a foggy, rainy evening when two humpback whales breached waters in defense of their young as transient orcas charged against them.

"What we saw was a lot of huffing and puffing from the humpbacks, orcas occasionally surfacing near or next to them, and occasional tail swipes. Much of it was in slow motion so I got the sense that there was a lot of maneuvering going on below, perhaps the adult humpbacks trying to block access to the calf," naturalist Valerie Shore said.

%

%

The transient orcas, or Bigg's killer whales, appeared to be going after the calf in Sunday's rare sighting. Though they usually prefer to gray whale calves, transient orcas do hunt humpback calves -- for their tongues. 

Executive Director of Pacific Whale Watching Association Director Michael Harris explained to KIRO 7 News that in an attack, the transient orcas hold down the calf and drown it. But the most recent case did not turn fatal, as the four adult humpbacks ran off the orcas in their protection the calf.

Though attacks can leave gnarly marks on the humpbacks, the encounters between the whales seldom result in a kill.

%

%

The short answer as to why attacks on humpback whales are happening isn't too grand of an explanation, and it doesn't have too much to do with the food chain. It's simply nature.

"We don't see it often [in the Salish Sea] because it's off the coast, but now that we have the 'humpback comeback' we have whales and calves and a record number of transients, it was just a matter of time," Harris said.

>> PHOTOS: Transient orcas becoming more familiar to PNW waters

>> PHOTOS: Large groups of humpback whales seen in Salish Sea

Sunday's interesting predation, as Harris calls it, wasn't the first of "Clash of the Titans" in local waters. Whale-watching crews captured an epic encounter off Everett between orcas and Saratoga gray whales off Everett in the spring.

The major altercation was another encounter where an orca's attack fell flat. The two gray whales survived the attack had no visible injuries.

%

%

"I've seen a lot of this over the years, but I don't think the killer whales have much success predating on them [other whales]. Perhaps the occasional calf, but even that would be rare," whale-watching captain and researcher Mark Malleson.

A limited necropsy of a young whale that died in shallow water off West Seattle on Sunday revealed that the animal had killer whale bite marks on its jaw. It could be possible the juvenile whale washed up after an attack, but the marks are only one of the contributing factors to the whale's stranding, as it was in poor nutritional health and had internal injuries.

PWWA crews are reporting unprecedented numbers of these massive, acrobatic humpbacks -- not just frequent reports of two or three whales in any one spot but now large groups of extremely active animals, as many as 15 or 20 together.

>> Related: Unprecedented sightings of large humpback whale groups in Salish Sea

>> Related: Transient orcas visiting northwest waters in record number

Whales have impressive memories and can retain knowledge of locations where they have been harassed, but whale researchers do not believe that orca attacks on humpbacks' young will deter them from the Salish Sea. 

"It seems they just like bugging them," Malleson said.

Whale watchers and researchers are still learning why Orca Country has become the so-called American Serengeti and what's been drawing these rare whales and dolphins into the Salish Sea.

Cox Media Group