Researchers in Russia have investigated the strange case of a female orca (Orcinus orca) whose body was found on a beach and contained seven otters that had been swallowed whole. Not only is this an unusual meal for this type of marine mammal, but the orca was washed up far away from its normal territory.
The orca’s body was found on the coastline of the Commander Islands (Komandorski Islands), in the Russian Far East in the Bering Sea, in 2020. During their investigation, the scientists discovered six of the sea otters (Enhydra lutris) inside the animal’s stomach, as well as one (described as a young male) that was stuck in the orca’s throat, at the junction between the oral cavity and the esophagus. It is possible this otter may have led to the orca’s death.
Together, the otter’s bodies weighed 117 kilograms (258 pounds). In addition, the orca had also eaten a large number of cephalopods (probably octopus or squid), as they found 256 beak parts in its gut.
Generally speaking, orca do not tend to eat sea otters. Instead, they prefer to hunt for seals, sea lions, dolphins, and whales (the orca's other name, “killer whale”, is actually an inversion of its original name, “whale killer”). This makes the otter-eating orca extremely unusual.
“The finding is very unusual,” Dr Olga Filatova, a cetacean researcher at Moscow State University, explained to IFLScience. This is because “killer whales normally do not eat sea otters - there were some observations of them harassing and killing sea otters, but very few proofs of actual consumption.”
In addition, orca tend to tear their food up and consume the best parts, so the fact that this specimen devoured multiple sea otters whole is even more strange.
“I am not sure why this particular whale tried to swallow seven sea otters in a row - maybe it was very hungry, or sick, or crazy,” Dr Filatova added.
The plot thickens
Another aspect of this orca mystery relates to where it was found. According to DNA analysis, the orca is part of a population known as “Bigg’s killer whales”, which have a home range that extends from the Aleutian Islands and the Gulf of Alaska to the coastline of California.
How the marine mammal came to be in the Commander Islands of the western North Pacific is completely unknown, but it is possible that it learnt its eating behavior – swallowing otters whole – from where it originally came from.
Another mystery solved
But while there is much we do not know about the circumstances that brought the animal to its final resting place, the orca’s remains may help answer other questions.
Since 2008, scientists have been noticing a decline in sea otter numbers in waters off Alaska and the Aleutians. The body washed up on the Commander Islands may indicate that orcas have been responsible for hunting otters in this region, as it is the first direct evidence of an animal originally from that population taking part in such predation. Ultimately, the analysis of the orca reveals valuable information for marine scientists.
“Investigating the stomachs of stranded killer whales is crucial to directly confirm feeding on particular species”, Filatova and colleagues wrote in their paper, “because visual observations often leave uncertainty as to whether an attack was a predation or just harassment, and feeding on species like squid is impossible to observe.”
The study is published in Aquatic Mammals.