Give an orca some fish, and he’ll eat for a day. Try to keep your fish from an orca, and he’ll figure out how to eat them — and teach all his friends to do the same.
Orcas, also known as killer whales, have long been known to dine on fish that people have caught in lines or nets. And a new paper examining the phenomenon paints a picture of how the socially complex animals respond to their environment being altered by human activity.
The paper, published in the journal Biology Letters, analyzed years of data involving two different killer whale populations near the Crozet Islands in the Indian Ocean.
Since the 1990s, the region has been a hotspot for commercial fishing of the Patagonian toothfish — a fish often marketed under the name “Chilean sea bass.” The toothfish are caught on longlines along the bottom of the ocean floor, meaning that one big fishing line is baited with many hooks and each hook nabs an individual fish.
As the lines get drawn up from the deep water, they essentially become “the open ocean equivalent of the conveyor belt in a sushi bar,” as Luke Rendell, a Scottish biology lecturer uninvolved with the study, put it in a piece for The Conversation.
The researchers looked at data from 2003 to 2018 and noted that incidents of orcas eating the fish off the hooks, referred to as “depredation,” gradually increased over time. This seemed to be due to individual orcas picking up the behavior from one another. One of the orca populations the scientists studied was first reported feeding off of fishery catches in 1996. By 2014, all 80 to 100 orcas in the group had started doing it.
In addition to the ease of snatching fish off of a fishing line, another reason contributing to the behavior catching on could be overfishing. In the 2000s, as the population declined, it became more difficult for orcas to catch toothfish themselves, but they then encountered “increased and predictable” opportunities to pluck their prey off of fishing lines.
Overall, the researchers were struck by how thoroughly commercial fishing had changed the orcas’ behavior over time.
“This study is illustrative of how human activities, by altering the availability of resources in ecosystems, may lead to new behaviours (sic) spreading across individuals of species capable of innovating in response to changes in their environment,” they wrote.