Crew aboard an Irish government research vessel caught sight of a dorsal fin belonging to a smooth hammerhead shark (Sphyrna zygaena) last week – making it the first sighting of smooth hammerhead shark in Irish waters, The Times reports.

Smooth hammerheads are apex predators and can reach lengths of up to 5 meters (16 feet), which is roughly equivalent to 1.5 Volkswagon Beetles. The shark's distinctive "hammer" bestows the creature with an improved binocular vision that makes it all the better for tracking down fast-moving prey and can also be used to trap said prey against the floor.

Smooth hammerhead sharks prefer the warmer waters of the tropics but have been known to venture north as far as Britain, with the most recently confirmed record being a head of one that washed ashore at Portreath, Cornwall, in 2004.

Experts suspect the latest sighting in the Celtic Sea, southwest Ireland, is a sign of rising ocean temperatures – and say we can expect more shark sightings of a similar ilk in the future. 

"It could be a very lost hammerhead shark, but more likely it is because our oceans are getting warmer," Simon Boxall from the National Oceanography Center, UK, told The Times. He pointed out that temperatures in the area have risen substantially over the past few decades, encouraging species typically considered "more exotic" to swim further north in search for food.

"There is no reason why more shark species like hammerheads and great whites can’t exist in our waters," Boxall added.

It is hard to refute the fact that oceans are getting warmer: data published by the Environmental Protection Agency (EPA) in 2016 shows global sea temperatures have risen, on average, 0.07°C (0.13°F) every decade, while a report published by the UK Government Office for Science predicts temperatures will rise 1.2 to 3.2°C (2.2 to 5.8°F) by 2100. 

All this is having an effect on marine life. We are seeing the number of sharks in and around the Great Barrier Reef drop, with large apex sharks (hammerhead, tiger, and white sharks included) seeing some of the most dramatic declines – 74 to 92 percent along Queensland’s coast since the 1950s, according to a study published last year.

Meanwhile, traditionally cooler regions – like Ireland and the UK – are attracting new visitors. There are currently 40 or so species spotted close to the UK coast but a 2018 study predicts 10 species of shark will migrate to the area by 2050 as ocean waters rise. This includes the blacktip shark, the goblin shark, and, of course, the hammerhead shark – which is frequently seen around the Spanish and Portuguese coasts but less so around the British and Irish coasts.

"I am sure these species [hammerheads and great whites] are more common than people realize, it’s just that they haven’t been seen," Boxall said.

"But it doesn’t mean we are going to get a mass invasion of hammerhead sharks."

[H/T: The Times]