In 2011, North Carolina scuttled the 180-foot Coast Guard buoy tender USCGC Spar off Morehead City; divers later documented sand tiger sharks using the wreck

The USCGC Spar was an 180-foot Coast Guard buoy tender, a relic of the past, just 30 miles offshore Morehead City, North Carolina, in approximately 100 feet of Atlantic Ocean. During the 53 years of her life, she hunted submarines, chased ice floes, and even made a tour of the entire North American continent in one go. She was decommissioned on February 28, 1997, and seven years later, in June 2004, North Carolina's artificial reef program placed her on the bottom of the ocean on purpose.

But what happened next was a surprise: the Spar didn't just turn into scenery. She was an easy target for one of the ocean's most misunderstood predators: the sand tiger shark, and a real-life example for marine biologists. A 2019 peer-reviewed study titled “Citizen science reveals female sand tiger sharks (Carcharias taurus) exhibit signs of site fidelity on shipwrecks,” published in the journal Ecology, reveals that sand tiger sharks off the North Carolina coast don't just pass by wrecks, such as the Spar. Female sharks often return to the same wreck, or to those nearby, years later, treating it more as a "home base" than a "pit stop".

The afterlife of a warship, and why it's more important than you think


The sand tiger is described by divers who often visit the Spar as a species that is slow, curious, and generally docile, more interested in gulping air to maintain buoyancy than in bothering someone with a camera. That gap between the shark's public reputation and its actual behavior points to something worth noting about American shark policy: for decades, conservation funding and public attention have leaned heavily toward sharks as threats rather than as animals in need of protection, though that's an interpretation, not a settled finding from any single source.

That's a differential that has implications. Sand tigers have painfully low reproduction rates, and overfishing has hammered their numbers, so much so that NOAA listed the species as one of concern in 1997, the same year the Spar was mothballed. Since then, the global population has been assessed as Critically Endangered on the IUCN Red List (Rigby et al., 2021), a worldwide rating that reflects an estimated population decline of more than 80% over three generations, though the Northwest Atlantic population that uses wrecks like the Spar is considered comparatively less threatened thanks to U.S. fisheries protections in place since 2000. That makes a random Coast Guard hull off Morehead City seem more like a plank of conservation infrastructure than a novelty dive site.

Citizen scuba divers, not the government, solved the mystery

The surprising part of the story is that a lot of what scientists know about how wrecks such as the Spar are used by sand tigers came from recreational divers, not government researchers. This information was collected from recreational divers who upload their own pictures. You can tell each sand tiger apart by its unique pattern of brown spots along its sides, much like a fingerprint, and by a citizen-science program called Spot A Shark USA, which tracks individual sharks through over a thousand identifications using software. It was how the Ecology study confirmed the presence of specific female sharks at the same wreck, even after 72 months.

The ecological function of shipwrecks is no accident

Zoom out and the Spar is just one piece in a much larger, stranger story. According to a 2024 review article titled "Shipwreck ecology: Understanding the function and processes from microbes to megafauna," published in the journal BioScience, most of the world's estimated three million shipwrecks were lost by accident or by war, and many now provide habitat for microbes, sharks, sea turtles, and other marine life. In North Carolina alone, dozens of old ships have been intentionally sunk as artificial reefs, and the practice is a happy accident of naval history becoming a marine biology treasure.

The more useful takeaway is that a piece of Cold War-era hardware, sunk for reasons unrelated to conservation, has likely provided meaningful habitat for an endangered species; not by design, but because a docile, site-loyal shark found a use for it. It's a small, accidental win, not a substitute for the kind of deliberate shark protection policy that's still largely missing in American waters.