It appears even killer whales don’t always feel like putting in the effort to hunt for their own food.
According to a new study, a group of orcas have been teaching each other to steal fish from human fishing nets.
In a study, published earlier this month in the journal Biology Letters, researchers looked at data from the Crozet Islands, an archipelago in the southern Indian Ocean, where killer whales currently take approximately 180 tonnes of toothfish a year from longlines belonging to a specific fishery.
Researchers tracked two subantarctic killer whale populations for 16 years, from 2003 to 2018, to investigate changes in how often they were feeding on fish that had already been caught by the fishery.
When a wild animal species adjusts their feeding patterns to take advantage of the presence of humans, such as stealing food out of nets or traps, it’s called “depredation behaviour.”
Sometimes, this occurs because human behaviour in a region disrupts the existing ecosystem, according to the study, depriving animals of food that used to be abundant. But this new study suggests that it’s a tactic that animals can pass on to each other.
According to the study, orcas are the most frequently reported mammal to engage in this behaviour,
Although it’s known that seabirds often feed from human fish catches, not many studies have focused on larger marine predators.
Researchers tracked two different types of orcas found to engage in depredation behaviour around the Crozet Islands: “regular” killer whales found in both shallower and deeper water that normally hunt seals, whales, penguins and fish as their natural prey, and “Type-D” killer whales, which are only observed in deeper waters and whose natural feeding habits are unknown.
Both types of orcas have been “monitored extensively” since the 1960s using a photo identification program operated both from the coast and from fishing vessels.
Researchers looked at data on orca depredation gathered with this program over the 16 year study period, and then applied the data to probability models.
They found that the number of orcas participating in depredation increased over the years, as well as the proportion of depredating killer whales in the “regular” group.
However, this doesn’t reflect population growth, as the population of the groups did not increase significantly over those years, with population growth of the “regular” killer whales actually on a negative trend.
“Therefore, increases in the number of depredating [killer whales] at Crozet are likely the result of existing individuals in populations developing depredation as a new behaviour during the study period,” researchers said.
In addition, the study reported adult killer whales that had previously only been observed eating seals and penguins, adjusted their behaviour late to add depredation over time.
Due to the social segregation between the two groups, researchers believe “regular” and Type-D orcas got the idea for stealing from humans independently.
However, the acceleration of more orcas within each type participating in depredation, particularly in the “regular” group, supports that individual orcas in each group spread the idea to one another.
“For regular [killer whales], individuals of which form a single social network whether depredating or not, this transmission may have been further promoted by groups associating more frequently with each other following the 1990s additive mortality event,” the study stated, referring to a sharp decline in population for this group, which occurred in the 1990s after illegal fisheries began shooting orcas for stealing their catch.
It’s not just a cool fact to confirm that killer whales can plot to steal from humans and then teach each other to do the same. Researchers explained that as humans and predators continue to share the same waters, these shifts in behaviour could have ripple effects across different species.
“Increasing numbers of individuals using fisheries as feeding opportunities, reaching a total of greater than 120 (regular and Type-D combined) at Crozet in recent years, may lead to changes in the role of [killer whales] as predators in local ecosystems,” the study stated.
