Around 150 dusky and sandbar sharks have gathered near Israel's Hadera Estuary. The predator meet-and-greet has been observed in years past, but it seems more individuals are joining in as time goes on.

The Hadera Estuary sits several miles from a near-shore power plant, and news of the sharks' arrival has sparked some concern online about their safety in these waters. The power station is run on coal, and while its emissions have been linked to spikes in air pollution (and there's no denying the health and environmental impacts of coal power worldwide), radioactive water is not high on the danger list. Like all rocks, coal does contain trace amounts of radioactive elements, but it does not follow that swimming near an energy station is inherently dangerous (more on that here). The same applies to nuclear power stations.

In other words, these animals won't be growing "Blinky"-style third eyes any time soon. But why are so many of them congregating here?

It is actually possible that the station's proximity to the sea has something to do with it. The Hadera plant uses ocean water to cool its turbines, and that water eventually makes its way back out. This means the estuary maintains a slightly higher temperature than the surrounding open ocean. 

"You can see [the sharks] are drawn to the warm water," Israel Nature and Parks Authority marine ecologist Ruth Yahel told AFP. "They enter its stream and perform a Rondo-like dance, fly out with the stream, circle around and do it again."

Some have speculated that the animals are moving inland to give birth, using the estuary like a nursery. We've seen this behavior with other sharks and rays, but not all species are equipped for it. Bull sharks in particular are well suited to mating in estuary mouths because they can adjust their biological processes to increase salt retention in brackish waters. This is also true of sandbar sharks, who, along with duskies, are part of the same genus (Carcharhinus) as their better-known kin.

Sandbar sharks are known to pop up in sweet-water hangouts worldwide, like Virginia's Chesapeake Bay. Duskies, on the other hand, tend to avoid low-salinity locations. This could explain why some of the Hadera sharks are moving in and out of the stream, rather than staying put.

It's also possible that the gathering is less about mating and more to do with an increase in available prey. Others have suggested the animals could be using the warm water to kill pesky parasites. "But these are all theories," says Yahel. "We don't know for sure."

Scientists will continue to watch the sharks' movements over the coming weeks, but in the meantime, officials have warned divers and tourists to maintain a safe distance. Sharks certainly aren't the killing machines they've been made out to be, but we all know what happens when animal selfies go awry. Feeding and harassing the sharks is strictly prohibited.


Top header image: Ken Tam/Flickr