Great White Sharks Hunt With Help From the Sun
Great white sharks, while not the monstrous man-eaters that pop culture makes them out to be, are peerless when it comes to hunting in the open ocean. Their place at the top of the oceans’ food chain is due in part to their speed, size, and highly developed senses, but there’s also some strategy involved—including one aspect that scientists have never seen before in any animal besides humans.
Sharks hunt primarily at dawn and dusk, and there’s a good reason for that. Earlier this year, researchers in Australia showed that great whites exploit the Sun’s low position during these times to help them stalk and attack their prey.
The researchers, led by biologist Charlie Huveneers, went out to sea in a boat off the coast of South Australia and enticed sharks to attack a chunk of tuna that they moved around on a fishing line to mimic live prey. They did this both in the morning and afternoon, on both sunny and overcast days. Whenever a shark went for the bait, they noted the fish’s sex, size, and any identifying marks, as well as the direction it approached from and the position of the Sun. During 30 of these trips over the course of a few months, they recorded 579 “predatory approaches” on their tuna by 37 different sharks.
On cloudy days, the researchers found that the sharks approached the tuna from all different directions, but on sunny days, a pattern emerged. On sunny mornings, the sharks mostly approached from the east, and primarily came at the tuna with the Sun directly behind them. In the afternoon, the sharks changed things up and mostly approached from the west—again, mainly with the Sun behind them.
The pattern didn’t correlate with factors like the position of the boat or wind direction, which would affect the dispersal of the tuna’s odor, leading the researchers to think that the sharks track the position of the Sun and exploit it while hunting.
This is the first evidence of any nonhuman animal using the Sun as part of their predation strategy, and there are several benefits for sharks approaching prey with the Sun behind them. First, Huveneers and his team say, it makes it easier for a shark to detect and identify potential meals because the Sun isn’t in the shark’s eyes. It also directly illuminates the side of the prey facing the shark and makes it stand out against the background.
Approaching from the same direction as the Sun can also help keep a shark hidden from its target. Prey whose heads are above the water, like seals or seabirds, would see glare on the water’s surface in the direction of the Sun, which would conceal an oncoming shark below the surface.
If this is in fact what the sharks are doing, it’s a pretty impressive skill. Sharks would need to keep track of the Sun’s shifting position over the course of the day, and its position relative to a moving prey target and during each approach. Adjusting their approach in response to two different changing cues isn’t a trivial cognitive task, the researchers say, and suggests we should be giving sharks more credit for having brains as well as brawn. In future studies, the team wants to explore the cognitive abilities that let them use this unique tactic.