A call for vulnerable sharks to be spared from fishing came from an environmentalist after pictures circulated via social media showed two dead tiger sharks aboard an unidentified boat.

Tiger sharks are not only under threat, but crucial to the health of the sea – and inedible, according to William Welton.

Mr Welton, chief operating officer at the Bermuda Institute of Ocean Sciences, said yesterday that he was speaking in a personal rather than official capacity.

He added there were quiet efforts under way by conservationists to have sharks afforded some protection from fishing, as their population around Bermuda was under threat.

“When the water gets this warm, it’s prime time for seeing tiger sharks,” he said. “This is a time when we should recognise they are very vulnerable and that, pending larger protection, we should just leave them alone.

“If you accidentally hook one, just let it go.”

Mr Welton said there was a dearth of hard science on the extent to which local shark populations were threatened.

“There’s a general feeling that it’s very plausibly from overfishing,” he said, pointing to heavy and “completely unsustainable” fishing of juvenile sharks as recently as the 1990s.

“Sharks are very slow breeders. They can’t take that kind of hammering. The strong suspicion is that we have almost extirpated sharks on the Bermuda platform – I think they have been wiped out near shore.”

Judging from the size of the fish in the pictures online, Mr Welton said one at least might have had shark pups inside.

Sharks have a long established place on the Bermudian menu, with shark hash among Cup Match favourites.

But Mr Welton warned: “With tiger sharks, there are a lot of reason why you would not want to eat them. Tiger sharks taste revolting. It also could be full of mercury.”

He added that the top predators’ meat could also concentrate the toxins that cause ciguatera, a painful illness that has struck residents in recent years after eating large predatory fish.

Tiger sharks, which have been studied along with other top species since 2005 under the Bermuda Shark Project, are usually sighted well offshore in locations such as Argus Banks.

Mr Welton highlighted a reverberation throughout the island’s marine environment from a loss of sharks, in part because the animals feed on sea turtles.

“We’ve had a huge boom in turtle numbers because there are no sharks,” he said.

“As a result, the turtles have almost wiped out seagrass, which is an extremely important habitat. You saw starved thin turtles desperately trying to find seagrass to eat.”

He said seagrass, which can form dense meadows, provided food and sanctuary to a wide range of life.

“It’s a habitat for all the reef fish that Bermudians like to eat, such as hogfish and groupers. Because of the loss of seagrass, the conch numbers are down, and our spiny lobster numbers are down.

“There is a massive knock-on effect because we have removed the apex predators.”