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Scientists Discover Remote Vast Breeding Grounds For Disappearing Bahamian Conchs

Researcher Phil Souza measures conch on Cay Sal Bank, where a team discovered one of the largest populations in the Caribbean.
Researcher Phil Souza measures conch on Cay Sal Bank, where a team discovered one of the largest populations in the Caribbean.

On a vast, wind-battered bank wedged between Florida, Cuba and the Bahamas, scientists studying the troubling decline of queen conchs have discovered some rare happy news: a thriving conch republic.

Among the highest ever documented in the Caribbean, researchers believe the herds grazing on Cay Sal Bank provide a lifeline to overfished Bahamian waters miles away.

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“If you use a cow analogy, it’s a great pasture,” said Andy Kough, a research biologist at Chicago’s Shedd Aquarium and co-author of a June study published in the journal Aquatic Conservation.

"Every single time we got in the water we found animals. Well, that's an exaggeration," he said, laughing. "It's like 80 percent of the time, literally."

Conchs on Cay Sal Bank collected for measuring.
Credit Amanda Weiler / Shedd Aquarium
Conchs on Cay Sal Bank collected for measuring.

Most Bahamian conch populations now fall below the threshold needed to survive. That’s despite increased efforts to save them with size restrictions and no-take zones. In 2017, Kough reported that one of the biggest populations in a protected preserve had dropped 71 percent in just five years. A more recent study found that shrinking numbers may no longer support commerical fishing in just 10 to 15 years.

With few regulations and high demand, Kough worries the Bahamas could follow Florida to a largely conchless future.

“It’s related directly to fishing pressure,” he said. “You have fishing that is greatly depleting this beloved animal.”

Based on the findings, Kough and lead author Phil Souza say conch fishing at Cal Say should be closed until more research is conducted to better understand the population. At the very least, they say, the bank should be used to provide a baseline for Bahamian conchs — which has never been calculated — since the Cay Sal conchs could be one of the last, largely untouched populations in the islands.

“It's very important to protect this bank so [the Bahamas] fully understands what they have," Souza said.

Up until now, just two other locations in the Caribbean have turned up higher numbers: in waters west of Puerto Rico and Cuba’s Desembarco del Granma National Park. But those surveys covered much smaller areas, about a fifth of the size of the Shedd’s 10-day trip. The Cuban survey also included smaller conchs not counted in other surveys.The largest number previously counted in the Bahamas, around the Grassy Cays, averaged 180 for every couple of acres. In Cay Sal, some locations had as many as 300.   “There were conch as far as the eye could see,” said Souza, who grew up diving for conch near his grandmother’s house on Great Exuma. “I had never seen that many conch in my lifetime.”

Diver Lashanti Jupp measures a queen conch.
Credit Amanda Weiler / Shedd Aquarium
Diver Lashanti Jupp measures a queen conch.

At more than 2,000-square miles, Cay Sal had long been rumored to have lots of conch.

Kough said he’d been told by local fishermen, who rarely make the long journey, that the bottom was littered with conchs. He'd started making plans to explore it while researching the decline in preserves, where he found overfishing in unprotected waters was drying up the supply of larvae carried by currents.

If Cay Sal did indeed have a trove of conchs, it could explain how some populations survived despite heavy fishing. With the fast-moving Gulf Stream running along the east side, larva essentially only get carried to the northeast — into Bahamian waters.

It also made sense that Cay Sal would be a conch haven. It's mostly shallow, between 30 and 50 feet deep, fringed by a reef and blanketed by seagrass meadows perfect for grazing. But getting there was not easy: Kough said securing permits and timing research with weather conditions took two years.

"A lot of people don't even know this place exists," he said. 

The bank is one of the largest atolls in the world, rimmed with 96 tiny islands, about 150 miles west of Andros Island.  The U.S. Coast Guard monitors Cay Sal island and the nearby Elbow Cays, which has an abandoned lighthouse, for strandings, especially by refugees fleeing Cuba just 30 miles away. Kough said a group washed up while the Shedd team was anchored nearby. 

Divers Amanda Weiler and Joletta Silver aboard a dinghy at Cay Sal. The Coral Reef II is in the background.
Credit Phil Souza / Shedd Aquarium
Divers Amanda Weiler and Joletta Silver aboard a dinghy at Cay Sal. The Coral Reef II is in the background.

“I've been to a decent number of fishing grounds around the Bahamas and I've never seen anything like Cay Sal," Kough said.Over 10 days, a team of 12 divers, including Souza and Kough, made more than 180 dives, leaving the Coral Reef II in dinghies to explore the vast bank. They dived mostly around rocks and tiny islands where they could escape choppy seas. On two days, conditions were too rough to leave the Coral Reef II. 

“We really only scratched the surface as far as surveying the bottom,” Souza said. “We think that if you were to go back in there and survey some of the less accessible parts of the bank, you would really see huge densities.”

And numbers matter when it comes to conch because they need to congregate in big herds to successfully reproduce. The slow-moving slug literally need to bump into each other.

"They have internal mating, which means a male and a female actually have to knock into each other," Kough said.

They believe the conch that inhabit the interior of the bank keep the local population healthy. Those along the edges likely produce larvae needed to resupply other parts of the Bahamas.

Before publishing the results, Souza said he and Kough considered the risk of drawing attention to the bank, which is better known for lobster and deep sea fishing off the nearby shelf. They suspect the faraway bank also gets a fair amount of undetected poaching drawn by the sizeable lobsters. In their research, poachers from the Dominican Republic accounted for about 1.8 million pounds of lobster in 2009 and 2010, about a third of the Bahamas annual export, they found.

Ultimately, they decided the prospect of getting better protections and monitoring, and drawing attention to the need to better study the conchs, outweighed the risks.

Cay Sal Bank sits between Florida, the Bahamas and Cuba and covers more than 2,000 square miles.
Credit Google Earth
Cay Sal Bank sits between Florida, the Bahamas and Cuba and covers more than 2,000 square miles.

"One of the most important things about protecting any animal is you have to know how many there are, where they are and what that population is like," Kough said. "For science, this is one of those places where you have, not a pristine population because it's been harvested down some, but one of the best case 'natural' populations that exist in the Caribbean today."

The bank was recently included on a list of areas to receive more protections under a national plan to protect 20 percent of Bahamian waters by 2020. But no rules have been finalized.

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