Queen conch dying out in the Bahamas despite marine parks

It’s hard to adequately describe the importance of conch to the Bahamas. Conchs are ingrained in the culture; there are conch festivals, conch homecomings and conch-cracking competitions. On the Bahamian coat of arms, a queen conch takes pride of place, sitting right at the top.

But new research finds that the queen conch (Strombus gigas), economically important as food and for its decorative shell, is facing unprecedented fishing pressure throughout its Caribbean range.

The study in the Marine Ecology Progress Series journal found widespread decline and an aging population among the conchs of the Exuma Cays Land and Sea Park (ECLSP), a marine protected area (MPA) in the Bahamas. The plight of this previously abundant and well-protected conch population is a troubling blow for this iconic marine mollusc.

“Besides being a staple to the local diet, harvesting and sale of conch supports entire island economies,” the Bahamas National Trust (BNT), a non-profit organization that manages the country’s national parks, said in a statement. Conch meat is an important part of the Bahamian economy; domestic consumption is difficult to quantify but exports alone bring in an estimated $3.3 million a year.

Not only are conchs economically and culturally important, but they also play a vital role in the marine ecosystem. Conch eggs and larvae, produced in the hundreds of thousands, are an important food source for a number of vulnerable and endangered marine creatures. Conchs also feed on the algae found on sea grass, preventing the sea grass from being smothered.

Fueled by a growing tourism industry and an expanding export market, demand for conchs skyrocketed in the 1970s. Bahamian fishermen were quick to capitalize: conch landings in the country rose from an estimated 750 tonnes per year in 1970 to a peak of 6,368 tonnes in 2006. Despite CITES listing conch as an Appendix II species in 1992, thus subjecting its trade to rigorous restrictions, fishing pressure continued to grow, and conservationists fear this large take of conchs is leading to population declines.

Conchs, which can live up to 30 years, do not reach sexual maturity till 3 to 5 years of age, meaning that declining populations can take a long time to recover. To add to their woes, conch breeding behavior relies on large spawning groups known as “aggregations.” If their densities fall below 47 adults per hectare (about 19 per acre), then they do not reproduce, further hampering their ability to recover from overexploitation.

The Bahamas’ extensive network of MPAs was previously a beacon of hope for the beleaguered conch population. The BNT banned fishing in the ECLSP in 1986, and an initial survey conducted in the early 1990s found conch densities as much as 31 times higher than surrounding fished areas. These early results were so positive that conservationists hoped the successful ECLSP population could help repopulate downstream fisheries.

However, repeat surveys in 2011 and 2016 highlighted an alarming downward trend.

“Despite the fact that the park has been generally well protected from fishing during the last 20 years, queen conch stocks have diminished substantially,” says Allan Stoner, a leading expert on the queen conch and chief scientist for the Community Conch conservation organization and co-author of the survey paper.

The team found a clue to the underlying cause of the declines in the increasing ages of conchs in the ECLSP. Once a conch shell has reached its full length, it starts to thicken, and scientists use this thickness of the shell to estimate age. The survey found predominantly old and large adults in the park, with a shortage of juveniles to replace them.

The team has two main theories for the lack of juveniles in the park. The first is that the ECLSP’s success may in fact be part of the problem.

“We think there may be a counterintuitive influence of protection on conch in the park caused by higher populations of predators,” says Andy Kough, research biologist with the Shedd Aquarium in Chicago and lead author of the survey study.

While very few predators besides humans are capable of breaching an adult conch shell, the developing shells of juveniles place them firmly on the underwater menu.

“It may very well be that higher populations of protected predators inside the park are devouring young conch before they are able to grow a big and thick enough shell to protect them,” Kough says.

The second theory is more worrying.

“Juvenile conch are not recruiting to the park from outside, and the park population is slowly dying of old age,” Stoner says.

In the free-swimming larval stage, young conch may be carried many miles along ocean currents. This means that the larvae produced by the breeding adults in the park do not stay within the park, making the ECLSP population dependent on a healthy breeding population upstream.

Scientists are now focusing on identifying the larval source for the ECLSP.

“We are primed to answer this question using new technologies such as biophysical modelling,” Kough says.

However, finding the larval source is only half the battle, as the situation for conch outside protected areas is bleak. Surveys conducted by Community Conch in fishing areas have revealed that queen conch populations in the Bahamas are near collapse.

In contrast to the ECLSP population, conch in fishing grounds have become younger with time as adults are harvested faster than they can be replaced. With a declining breeding population, Stoner says the prognosis is unmistakable: “When there are no juvenile conch in the nurseries, there can be no subsequent fishery.”

For Kough and Stoner, it’s clear that the primary driver of the conch decline in the Bahamas is overfishing. Stoner believes conch fishery management needs to be reformed if Bahamian conchs are to have a sustainable future.

This sentiment is echoed by the BNT, which says that while enforcing current regulations is an issue, the regulations themselves need refinement. It suggests that regulations such as the requirement that conchs must have a “well developed and fully flared lip” before being harvested are imprecise and open to interpretation.

To compound the issue of imprecision, previous research by Stoner has shown that a fully flared lip does not indicate the point of sexual maturity. As a consequence, conchs are being legally harvested before they have had a chance to reproduce, thereby crippling the fisheries future.

Another key issue Stoner identifies is the growing use of surface-supplied air systems that allow fishermen to access conchs previously out of reach to free divers — effectively meaning no conch is safe from fisheries.

Time may be running out for the conchs of the Bahamas. It’s a pattern that has played out before across the queen conch’s range: collapsed populations and closed fisheries in Bermuda, Cuba, Colombia, the United States, Mexico and Venezuela offer an uncomfortable vision for the future in the Bahamas should things not change.

Attempts to reintroduce conchs in other areas have proved unsuccessful, with low survival rates and high costs. For example, the collapsed Florida fishery has still not recovered after 30 years, despite a complete fishing ban and a number of reintroduction efforts. With no backup option, conservationists say protecting existing wild stocks now is imperative.

Current efforts in the Bahamas are centered around a national “Conchservation” campaign that began in 2013. Conchservation is a widespread collaboration between the BNT and a number of government and non-government organizations. Through a mixture of public awareness, research and policy change, the campaign aims to create a sustainable conch fishery in the Bahamas.

The BNT says Conchservation has received a mixed response: “People want to protect conch but no one wants to change their behaviour or legislation to protect it.”

Research of the Bahamian queen conch population is on going. Video Credit: Shedd Aquarium

Conservationists have proposed a number of potential measures such as a closed season, quotas, export bans, bans on surface-supplied air systems, or a standardized lip thickness (to ensure conchs have time to breed before being taken). The BNT is finalizing its position on the specific regulation it intends to pursue through the Conchservation campaign. (The government formally recognized the BNT as an official adviser to government in 2010, placing the organization in an ideal position to influence policy.)

Commenting on the recent study of the ECLSP, the BNT emphasizes the importance of an MPA network that encompasses the entire life cycle of the queen conch. With the BNT overseeing the Bahamas’ pledge to protect 20 percent of its marine coastal habitat by 2020, there is hope that this may soon become a reality.

Possibly the greatest challenge for conch advocates will be to convince policymakers that the economic cost of protecting conchs is necessary and worthwhile. The marine resources minister, V. Alfred Gray, made clear in 2013 his opposition to an export ban. “It could be catastrophic to the Bahamas and the fishers of the country [to end exports] because we do not have too many industries,” he said in a speech.

As is so often the case, the fate of the queen conch in the Bahamas will ultimately depend on the action or inaction of the islands’ government.

“Of course all of these options require rigorous enforcement of the regulations,” Stoner says. “Increased political will is needed for any changes to occur.”

References:

Kough, A. S., Cronin, H., Skubel, R., Belak, C. A., & Stoner, A. W. (2017). Efficacy of an established marine protected area at sustaining a queen conch Lobatus gigas population during three decades of monitoring. Marine Ecology Progress Series, 573, 177-189.

Stoner, A. W. Mueller, K., Brown-Peterson, N., Davis, M., & Booker, C. (2012). Maturation and age in queen conch (Strombus gigas): Urgent need for changes in harvest criteria. Fisheries Research. 131. 76-84.