When you go after the same fish as a goliath grouper, you may be in for a tug of war—as a fisherman recently learned on a dive off Apalachicola, Florida.

Grayson Shepard was spearfishing for snapper at a shipwreck site in June when he captured a startling video of several goliath groupers trying to take his catch.

After a series of tussles, one of the groupers bends Shepard's spear “so badly it will no longer load into my speargun,” Shepard told National Geographic by email. At one point, several goliaths went after Shepard’s catch at once—and he was briefly pulled along for a wild ride. ("Watch: Grouper Slurps Down A Shark, Not A Typical Meal.")

“I weigh 220 lbs. [100 kilograms], and it dragged me easily 20 feet [6 meters] or so before letting go,” Shepard says.

As their name suggests, goliath groupers are true underwater giants, reaching 8 feet (2.4 meters) long and weighing up to 800 pounds (360 kilograms). (See National Geographic magazine's stunning pictures of goliath groupers in the wild.)

Native to shallow reefs and coastal waters in the western Atlantic and Gulf of Mexico (see range map), the fish were once aggressively hunted, and have been protected from hunting in the U.S since 1990.

Ambush Hunters

In the new video, the goliaths appear to become the hunters themselves, stalking Shepard and waiting for just the right moment to grab the fish.

“[Were they] following the diver around? No question about it. They probably know his boat by the sound of it,” says R. Grant Gilmore, a fish ecologist at the Florida-based company Estuarine, Coastal and Ocean Science, Inc.

Gilmore, who has studied the fish for decades, says goliath groupers are ambush predators that "prey predominantly on slow-moving animals. A speared snapper on the end of a spear-gun is a slow-moving animal,” says Gilmore.

He adds that goliaths, which can live up to 50 years, are smart enough to learn and remember human behavior. (Watch a video of goliath groupers spawning.)

“If a diver tries to shoot him, that’s it—he knows that. They’re very intelligent.”

Sylvia Earle, National Geographic Explorer-in-Residence, also suggested looking at the incident from the fish's perspective.

"Thinking like an ocean, it is clear that the diver, not the grouper, is doing the stealing," she says by email.

Photographer Swims With Huge Goliath Groupers

"What is a grouper supposed to do, anyway, when a fish is injured in the neighborhood?

Dinnertime!"

Protected… For Now

Goliath groupers have slowly rebounded in Florida, and despite being protected, Gilmore says goliath poaching is common, and he fears fishing the behemoths could become legal again.

“The goliath grouper has an ecological role in that it is the top predator" of the reefs, says Gilmore. “If you take the top predators out, you have an imbalance.”

What's more, Gilmore says the goliath grouper may be our best hope for controlling invasive lionfish, which are wreaking havoc on native fish species in the Atlantic. It just so happens that they're a favorite snack for goliath groupers. (Also see "Pictures: Sharks Taught to Hunt Alien Lionfish.")

As for Shepard, the spear fisherman, he says he has a lot of respect for the mighty fish.

“As frustrating as it is to lose my catch to them, I respect the laws protecting goliaths and will never physically harm or kill them,” he says.

“As apex predators, goliaths fill a niche in that ecosystem in which I am just a temporary visitor. We are targeting the same prey and it is well within their right to fight me for what is already theirs.”