Sarasota, Florida - The goliath grouper, a colossus of a fish that can weigh up to nearly 800 pounds, is the delight of divers in Florida, though scientists warn their numbers are down since the state allowed fishing of the giants to resume.

"There's nowhere else you can have an experience with a fish that big while you're diving – and being this close to it," Dr. James Locascio, a marine biologist with the Mote Marine Laboratory, told AFP.

"And so, really, we feel that the fish is worth a lot more alive than it is dead."

During a sea trip early this month off Boynton Beach, on Florida's Atlantic coast north of Miami, divers were amazed by these giants, which can measure up to eight feet long.

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With naturally down-turned mouths, these creatures may appear cranky, but some actually allow themselves to be brushed by a human hand.

"We were totally amazed about the amount of groupers that show up to the Boynton Beach area," diver Ben Galemmo told AFP.

Still, he added, "from talking to the locals, (the population) has actually gone down in numbers" in recent years.

A recent study confirms that trend.

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"The diving industry has reported that they are seeing fewer and fewer of these fish," said Locascio, the marine biologist.

That could devastate the local diving business.

Last year, when researchers with the Mote laboratory repeated a census of spawning sites first conducted in 2013, they observed significantly fewer goliath groupers in five of the six locations studied.

Overfishing had left the species near extinction in the 1980s, but conservation efforts saved it. Goliath grouper fishing was banned for more than 30 years.

But in the past year Florida authorities deemed the population had recovered sufficiently, and allowed 200 of the fish to be caught and killed each year in state waters.

Unfortunately, the goliath grouper lends itself to overfishing partly because it grows slowly – it can live as long as 30 years – and takes a relatively long time to reproduce.

The goliath is now classed as a "vulnerable" species by the International Union for Conservation of Nature, according to Locascio.

"We do not want its population to decline," he added, calling the fish "an essential species for maintaining the balance of the ecosystem."

The huge fish also lives in the waters of the Gulf of Mexico, the Caribbean, and off the coast of Brazil.