Who, What, Why: Why did giant fish hurl themselves at rowers?

Asian carp Image copyright AP

Giant Asian carp were filmed propelling themselves through the air at a college rowing team in Missouri, US. Why were they doing it, asks Tom Heyden.

They've been called the "Terminators of the fish world". They've been accused of "bludgeoning boaters". It's fair to say Asian carp have attracted a pretty bad reputation. And when an innocent team of young rowers are apparently ambushed by them, perhaps that's understandable. The scenes look like a sequel to Alfred Hitchcock's The Birds, resembling some sort of aquatic apocalypse.

The biggest Asian carp can weigh more than 100lbs (45kg) and stretch 4ft long, explains Viv Shears, the director of VS Fisheries. "Imagine if one of those hits you," he says. "There's certainly been cases of people being knocked out of boats [or] knocked unconsciousness." Incidents like these have not helped the Asian carp's public image. "Gang of Flying Asian Carp Mount Aerial Attack," was how one article reported the video.

But the ferocious terminology can be somewhat misleading. "It's not an aggressive attack, it's an escape mechanism," explains Shears. The carp get spooked by a boat's movement, triggering a fight or flight reaction, he says. And given their lack of any killer instinct, adds Shears, they opt for the latter. "Often the quickest way out of that situation is to go airborne." The first carp to jump at the perceived predator then sparks the sort of mass anxiety attack reminiscent of a Tom and Jerry scene involving a room full of mousetraps.

The carp are powerful enough to propel themselves out of the water, says Shears, but mainly it's because the key culprits - Silver carp and Bighead carp - often feed near the water surface. "[Many] other species would be on the bottom and shoot off [from there]."

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Media captionPallob Ghosh on the Asian carp's threat to the US Great Lakes

But while "carp attacks" are more panic than predation, don't expect any improvement to their PR. Although non-predatory - feeding on plankton and algae - Asian carp are voracious eaters and rapid breeders, meaning they can destroy ecological systems. "They don't directly impact upon other fish species but because of their numbers they take out the bottom of the food chain," explains Shears. Since their introduction into southern US states in the 1970s, Asian carp have sparked their own mass panic attack. After escaping into the Mississippi River, this "invasive species" has reached Chicago's canal system, prompting $18bn (£11bn) plans to "go to war with Asian carp" and protect the ecology of the Great Lakes, as shown in the 2014 video above.

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