Off the east coast of Australia, fish are doing something funny. On two separate occasions, biologist Ryan Day has seen needlefish employ a novel hunting tactic, launching themselves out of the water and attacking their prey from the air.
As far as he knows, Day says, “this is the first report of a fish leaping from the water to facilitate predation on other fishes.”
Needlefish, also known as Long Toms, live up to their name. They’re long and slender, and have long jaws lined with plenty of sharp teeth. They live and feed close to the water’s surface and are known for leaping out of the water to make quick escapes from their predators. They can launch out of the water at around 40 miles per hour and even skitter across the surface on their tails. Day says the fishes’ “proclivity for going airborne has resulted in severe injury and even death to people struck by needlefishes” while boating or swimming.
While watching needlefish hunt small baitfish around Australia’s Heron Island, Day saw the fish put these leaps to another use. After stalking their prey and moving in on them slowly, some of the needlefish proceeded with what’s considered their typical approach, swimming through the school of baitfish and then lunging through the water at a targeted fish.
Other needlefish, though, took a different tack. As Day and his colleagues report in the Journal of Fish Biology, as the needlefish neared their prey, they made a “leaping attack,” jumping out of the water and plunging back in right in the middle of the baitfish school, where they nabbed a fish in their jaws. These leaping attacks weren’t flukes: They accounted for half of the attacks the researchers observed.
The researchers saw the same thing while doing field work in another spot near North Stradbroke Island. Here, the needlefish made their leaps from the breaking fronts of waves, the team writes, “appearing to use the energy of the waves to propel them forward.”
The biologists think there are a few reasons needlefish might take to the air to make their attacks. First, the method extends the range they’re able to strike from. Needlefish typically lunge at their targets from around 1.5 feet away. At Heron Island, the fish started their leaping attacks when they were six feet away from the targets, increasing their attack range fourfold. This lets them strike sooner and from farther away, giving their prey less time to see them and escape.
Aerial attacks also rob the prey of an escape path. When needlefish attack while in the water, the scientists saw, their prey often flee like the needlefish themselves do, leaping out of the water and skittering across the surface. Attacks from above cut the baitfish off from this route, though, and force them to scatter and swim deeper.
It’s also possible that the needlefish are jumping out of the water to hide from their targets. Because of the way light bends as it moves from air to water, a fish’s view of the sky when it looks up at the surface is condensed into a tight circle, creating an "optical manhole" effect known as Snell’s Window. Outside the window, things appear dark or mirror the ocean’s depths or floor. An object in the sky directly above the fish would be pretty clearly visible and appear at full size, the researchers explain, but an object at the boundary of Snell’s Window would appear smaller, dimmer and even blurry or broken up. To a fish, these objects would look farther away than they really are, or might be hard to see at all. The researchers think that the needlefish may be taking advantage of this effect, and jumping into the air to disappear from their prey’s sight right before an attack.
Needlefish aren’t the only fish to use Snell’s Window—or the open sky—to their advantage. Their cousins the flying fish are well known for leaping out of the water and launching themselves at shallow angles to hide from predators on the edges of the optical manhole. And while needlefish are the first to use aerial attacks on prey in the water, other fish sometimes leap out of the water to grab prey in the air. Just last year, scientists in South Africa documented tigerfish leaving the water to attack birds mid-flight.