Ridgeback Sharks: Offshore Giants of the Gulf Coast

Ridgeback sharks, including silky and dusky species, are more commonly found offshore than along Gulf Coast beaches, according to marine experts. The category takes its name from the prominent ridge of skin running along the sharks’ backs between the dorsal fins, a distinguishing feature shared by a handful of large open-ocean species that roam the warm waters of the Gulf of Mexico. While their name surfaces in fishing reports and social media posts every summer, swimmers are unlikely to ever share the water with one — the ridgebacks live their lives far beyond the sandbar, in the deep blue water where the continental shelf drops away.

Dr. Sean Powers, director of the University of South Alabama School of Marine and Environmental Sciences and senior marine scientist at the Dauphin Island Sea Lab, says ridgeback sharks have been overharvested for years because of the desirability of their fins for shark fin soup. The Dauphin Island Sea Lab, located on the eastern tip of Dauphin Island at the mouth of Mobile Bay, serves as Alabama’s marine research and education center, and Powers’ dual role connects the university’s academic programs with the Sea Lab’s decades of Gulf research. His assessment of ridgeback populations reflects both what the science shows and what commercial fishermen have reported for years.

“These are sharks, like silky, dusky. Those sharks are not that common. They’ve been over harvested for years because of their fins,” Powers said. “So they’re going to be offshore. They are really slow to reproduce. They only reproduce every couple of years and they go on large coastal migration.” The reproductive pace he describes is the key to understanding why these animals remain scarce: a female dusky or silky shark may take years to reach maturity, carry a small litter for a long gestation, and then wait a year or more before reproducing again. Populations built that slowly can be stripped down quickly and take decades to rebuild.

The Global Trade That Shaped Their Numbers

The pressure on ridgeback sharks traces largely to the international trade in shark fins, which for decades prized the large, high-quality fins of silky and dusky sharks for shark fin soup, a traditional delicacy in Chinese cuisine. Fishermen targeting the fins have historically had little reason to release the shark itself, and the value of the fin gave the practice an economic engine that outpaced the animals’ ability to reproduce. Large coastal and oceanic sharks in the Atlantic have been subject to stricter management in United States waters since the 1990s, when federal law began restricting shark fishing, banning finning in federal waters and setting quotas and permit requirements.

Those protections have helped, but recovery is measured in decades for species that reproduce every couple of years. Silky sharks, once among the most abundant sharks in the open Gulf, and dusky sharks, the slowest-reproducing of the ridgebacks, remain at fractions of their historic numbers. That scarcity is exactly why experts like Powers point to the open ocean when people ask about them: the remnant populations cluster offshore, where the food is and where fishing pressure, while still a threat, has been curtailed by regulation.

Size and Diet

Ridgeback sharks can grow to about 16 feet and weigh up to 400 to 500 pounds, though most are in the 10-foot range. A shark of that size commands attention in any water, but in the open Gulf it is a mid-level player in a food chain that runs from small schooling fish to tuna, billfish and larger sharks. The animals are built for the open ocean, with streamlined bodies and powerful tails suited to covering vast distances in search of prey.

They primarily eat large fish like tunas and are often seen by fishermen fishing for tuna offshore. That shared taste for tuna puts ridgebacks on the same grounds as the charter fleets and sportfishing boats that run deep out of Alabama ports such as Orange Beach and Dauphin Island, sometimes trailing the boats for hours and drawing a mix of awe and frustration from crews battling a tuna to the boat. “So most of your viewers, the fishermen will see them when they’re fishing for tuna and things like that so far offshore,” Powers said. Anglers who venture beyond the shelf, toward rigs, wrecks and deep-water float lines, are the ones most likely to cross paths with a ten-foot shadow circling beneath the boat.

The Gulf’s offshore ecosystem makes those encounters possible. The deep waters beyond the continental shelf, punctuated by oil and gas platforms and natural features that attract baitfish, concentrate tunas, mackerel, amberjack and the sharks that hunt them. Fishermen working those waters learn to land a tuna quickly, because a lingering fight in shark country often ends with a smaller fish and a hard lesson about who else is hunting down there.

Not a Threat to Swimmers

While ridgeback sharks are not considered a significant threat to swimmers because they prefer deeper waters, they could potentially be encountered by divers. The species profile simply does not match the nearshore environment: silky and dusky sharks hunt in blue water over the shelf and beyond, following tuna and other pelagic fish rather than patrolling beaches for food. The sharks that draw lifeguard flags along Alabama’s beaches — small blacktips and spinners that chase bait schools through the surf — are a different group entirely, smaller, faster and far more visible in shallow water.

“Potentially they may be a little deeper than a normal depth there for a diver. So they’re very, very cold fish, but they’re not much of a threat,” Powers said. His point about depth and cold captures the biology: these are animals of cooler, deeper water, and encounters with divers happen at the edge of their range rather than in the shallow, warm water most Gulf visitors swim in. For divers working wrecks and ledges beyond the shelf, a ridgeback passing in the blue is a spectacle to appreciate rather than a danger to flee.

Reading the Gulf’s Shark Numbers

Understanding where ridgebacks fit in the Gulf’s shark community helps explain the offshore pattern. The Gulf hosts dozens of shark species across distinct habitats: small coastal sharks like Atlantic sharpnose and bonnetheads work the shallows year-round, blacktips and spinners patrol the nearshore surf, and the big pelagic species — silkies, duskies, blue sharks, makos and hammerheads — live over and beyond the continental shelf. Each group fills a different role, and each tells a different story about the health of the Gulf.

The ridgebacks sit near the top of the offshore food web as predators of large fish, which makes them useful indicators of how the open-water ecosystem is doing. A fishery with plenty of large sharks generally has plenty of prey beneath them; a fishery where the big sharks have thinned out is one where something upstream has gone wrong. Researchers at institutions like the Dauphin Island Sea Lab track those signals through longline surveys, fishery observer programs and tagging studies that follow sharks across their large coastal migrations.

Those migrations are part of what makes the species hard to study and protect. A dusky shark tagged off Alabama may travel down the Florida coast, into the Caribbean or around the Gulf in the course of a year, crossing state lines, federal boundaries and international waters along the way. Conservation measures that work in one jurisdiction can be undone in another, which is why scientists argue that highly migratory species demand management across their entire range rather than in one jurisdiction at a time.

What It Means for Gulf Coast Anglers and Beachgoers

For the fishing community, the experts’ message carries practical weight. Anglers who target tuna and other offshore species are the most likely people on the Gulf to encounter ridgebacks, and knowing that the animals are slow to reproduce — and that federal rules protect dusky sharks in particular — matters when a shark takes a hooked tuna. Handling gear carefully, keeping fights short and releasing sharks promptly when required gives depleted populations their best chance to recover while keeping anglers on the right side of the regulations.

For beachgoers, the takeaway is simpler. The sharks making headlines offshore are not the ones cruising past the sandbars at Gulf Shores or Dauphin Island. Ridgebacks keep to deep water, their populations remain reduced by decades of overharvesting, and their reproductive biology means they will stay uncommon near shore for the foreseeable future. Swimmers worried about sharks are far more likely to see the small coastal species that follow bait schools through the surf than any of the big offshore predators. The presence of a ten-foot shark offshore is, in its own way, a good sign — evidence that a recovering population is still out there, hunting tuna in the blue water where it belongs, a long way from anyone’s beach towel.