Richard Collins: Why would whales kill porpoises they don't eat?
A harbor porpoise calf being balanced out of the water. The porpoise eventually swam away, and its survival outcome was unknown. Picture: Candice Emmons, taken under NOAA permit #21348
Killer whales, despite their name, are relatively benign creatures, which only target their victims for food. Recently, however, the gentle giants were ‘outed’ — they have been blotting their copy-books.
In 1991, at a marine park near Victoria in Canada, trainer Keltie Byrne entered a pool which had two female killer whales and a male. It was the first time she had been in the water with them. The females seized Keltie, tossing her back and forth between them. The male, named Tilikum, joined in. The unfortunate trainer drowned.
Tilikum was moved to Seaworld Orlando. One morning in July 1999, the body of 27-year-old Daniel Dukes was found draped over the whale’s back. Dukes had hidden in the park at closing time and entered the whale pool during the night. Then, in 2010, Tilikum seized trainer Dawn Brancheau in front of terrified spectators and dragged her under the water where she drowned. Her long hair may have become lodged in his teeth, but witnesses claimed that the whale had grabbed her by the arm.
That a free-spirited wild creature, imprisoned within the narrow confines of an aquarium, turned ‘bolshie’ was hardly surprising; Tilikum had probably gone mad. However, in 2020, reports surfaced of killer whales attacking sailing yachts off the Spanish-Portuguese coast in apparently mindless acts of vandalism. By 2023, more than 500 such incidents had been reported. Three boats had been sunk. Unlike Tilikum, these whales were free-living.
For decades, orcas have been observed harassing and even killing porpoises without consuming them—a behavior that has long intrigued scientists. A study from @WildOrcaOrg and #UCDavisVetMed’s @SeaDocSociety investigates what may be behind it.https://t.co/OroczEawmH
— UC Davis Veterinary Medicine (@ucdavisvetmed) October 3, 2023
Now another complaint has been investigated by scientists. The Southern Resident Group of killer whales in the Pacific has only 78 members. They live almost exclusively on fish, mainly endangered Chinook salmon. Attacks on porpoises by these whales were reported as far back as 1962, but were dismissed as one-off freak occurrences. Since then, however, 78 such incidents have been documented. Most oddly, the whales don’t eat the carcasses of their victims.
That a predator, capable of killing seals and sea lions, should attack porpoises is not surprising, but why are these whales killing porpoises which they don’t eat? In a paper just published, 20 experts try to answer this question.
The simplest explanation they offer is that the whales are engaged in ‘social play’. Many creatures play just for the fun. Dolphins surf the bow-waves of ships for example.
Or, perhaps, the whales are honing their hunting skills. Domestic cats don’t always kill their victims immediately. They will release and recapture an unfortunate mouse repeatedly. Chinook salmon are agile fast-moving creatures, difficult to catch. Young porpoises need hunting practice. Similar in size and behaviour to adult salmon, dolphins might serve as proxies.
But the scientists suggest another, more humane, possibility: ‘mis-mothering’. Southern Resident whales have few young and 70% of pregnancies end in miscarriage or infant death. Are porpoises an emotional substitute for absent whale babies? Adoption of orphan calves has been recorded among killer whales elsewhere. They sometimes carry the bodies of their dead calves around with them. One did so for up to 17 days. Do adopted porpoises drown trying to emulate the behaviour of baby whales?
Killer-whales have a dark side. Have they also a soft side?
Nobody’s perfect!
