Sightings of killer whales have become less common in Antarctica's Ross Sea over the last decade.
Now, researchers are blaming a fishery that is catching the whales' main source of food.
While studying penguins in Antarctica, the scientists kept track of killer whales swimming by. They noted fewer each year - sightings fell from 120 to 26.
In an upcoming issue of Aquatic Mammals scheduled to be published online next week, the researchers will report that the decline is statistically significant.
The reason, they speculate, is that fishing boats are targeting the same large Antarctic toothfish that the whales eat, forcing the animals to hunt across wider areas.
The extra energy required could possibly result in fewer offspring.
What will be the main motivation for humanity's future space endeavours?Related story: (See story)
The cost of losing nature