We've seen the lengths false killer whales will go to for a mahi-mahi meal – but that taste for game fish has put them in competition with another group of predatory mammals in recent years: humans. The whales' open-ocean foraging grounds overlap with many commercial fisheries, and for the first time, scientists in Hawaii have recorded the cetaceans in the act of snagging the boats' bounty.

It might not look like much, but by the time this animal came into focus, it had already removed three baitfish from their hooks. Commercial longlines drape a whopping 30-60 kilometres (19-37 miles) in the water column, and false killer whales (Pseudorca crassidens)* are frequently caught as bycatch. It's likely that the behaviour in the video – known as depredation – has something to do with that.

To find out more, a team coordinated by marine biologist Aaron Thode modified surveillance techniques first used to study depredation in Alaska in order to put them to work in Hawaii. Analysing how false killer whales go about their fishy plunder, the team reasoned, might help them develop countermeasures.

"This was a true collaborative effort with fishermen," says team member Janice Straley, a professor of biology at the University of Alaska Southeast.  

Along with a GoPro camera, the team dropped sound-recording tech and a vibration detector with a longline off Hawaii's coast. They found that the whales made specific clicks and whistles while approaching longline baitfish.

"This study addresses some important questions about the nature of this depredation, and whether underwater sound can be used to study or possibly alleviate the issue," says Thode. Vibrations created by the clicks helped the team zero in on how loud the whales' echolocation can be. This could, in turn, allow fishermen to calculate how many whales are in their bait zones – and how far away they are.

"Fishermen [would] hear the animals make these whistles or echolocation noises before they deploy their gear," said Thode. That's helpful intel for preventing bycatch, but the team suspects that with a bit more analysis, we can also learn to differentiate the tugs and jerks made by different species. 

"This might lead to new ways to recognise and reduce bycatch, protecting both animals and fishermen from unintentional encounters," the team adds. 

For an up-close look at these orca doppelgängers, check out this rare footage!

Like orcas, false killer whales belong to the family Delphinidae. They are the fourth-largest of the oceanic dolphins, but it’s also acceptable to call them whales. That’s because the entire group is nestled under the sub-order Odontociti, or the toothed whales.


Top header image: Jim McLean/Flickr