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Gruesome video footage reveals ‘freshwater killer whales’

Gruesome video footage reveals what one scientist is calling the discovery of “freshwater killer whales,”  according to Discover Magazine’s “Not Exactly Rocket Science” blog.

Discover’s Ed Young writes that Julien Cucherousset from Paul Sabatier University in Toulouse, the researcher who coined the term “freshwater killer whales,” spotted the European catfish feeding on pigeons after local fisherman alerted him to their unique behavior. Mr. Cucherousset filmed the catfish from a bridge overlooking the island where the pigeons were cleaning themselves.

Not only do these catfish feast on pigeons, they also lunge out of the water to grab their prey, beaching themselves for several seconds before wiggling back into their natural environment.

The catfish are using one of three ways that predators hunt when their prey is located outside of the species’ ecosystem boundaries (land, for example, is outside of the catfish’s ecosystem boundary). According to researchers, predators can lie in ambush until the prey cross into their ecosystem, they can force the prey to enter their ecosystem or they can cross the ecosystem boundary to capture the prey.

“The behavioral strategies developed by predators to capture and kill their prey are fascinating, notably for predators that forage for prey at, or beyond, the boundaries of their ecosystem,” the authors contend in the journal PLOS ONE.

European catfish, the largest freshwater fish in the world, were spotted crossing into another ecosystem on a small gravel island in the River Tarn where pigeons like to bathe and wash themselves.

Researchers believe that their observations are unique to this species of catfish in this area of the world. They theorize, however, that other species may learn to adapt their hunting techniques to capture prey in new environments.

“Since this extreme behavior has not been reported in the native range of the species, our results suggest that some individuals in introduced predator populations may adapt their behavior to forage on novel prey in new environments, leading to behavioral and trophic specialization to actively cross the water-land interface,” they write.

Researchers suspect that the catfish sense the vibrations that the pigeons create with their wings and feet when they clean themselves in the water. The catfish likely use their sensitive whiskers on their upper jaws to feel the vibrations.

“These findings suggest that this new predation behavior might represent an extreme example of the ability of introduced species to adapt to a new environment that could have unexpected implications for consumer-resources dynamics and ecosystem functioning that deserve further investigations,” they add.