Introduction
For a long time, humanity's relationship with the ocean has been primarily extractive, and as wild-capture fishing practices have boomed and peaked, the majority of global fish stocks are now fully exploited or overexploited (McCauley et al., Reference McCauley, Pinsky, Palumbi, Estes, Joyce and Warner2015; FAO, 2024). This has led to less productive ocean ecosystems, a situation further compounded by habitat degradation and climate change (Pauly et al., Reference Pauly, Christensen, Guénette, Pitcher, Sumaila and Walters2002; Rogers et al., Reference Rogers, Griffin, Young, Fuller, St. Martin and Pinsky2019). Despite these declines, the ocean remains vital for the food security and livelihoods of millions of people. With careful planning, local fisheries management supported by international agreements can reverse the negative trajectories of marine species and ecosystems (Edgar et al., Reference Edgar, Stuart-Smith, Willis, Kininmonth, Baker and Banks2014; Duarte et al., Reference Duarte, Agusti, Barbier, Britten, Castilla and Gattuso2020). For example, sustainable fishing practices and management can yield economic and ecological benefits in tandem with food security (Costello et al., Reference Costello, Ovando, Clavelle, Strauss, Hilborn and Melnychuk2016). Species conservation status assessments and international conventions can help highlight threatened species, protect local populations and control trade in threatened species, and conservation agreements can help nations commit to setting aside areas as marine managed areas focused on replenishing ecosystems (O'Leary et al., Reference O'Leary, Winther-Janson, Bainbridge, Aitken, Hawkins and Roberts2016). A combination of marine managed areas, local fisheries conservation tools, and controls on trade is needed to maintain livelihoods, food security and biodiversity. Marine aquaculture has also been suggested as an approach to enhance food security given global human population growth (Costello et al., Reference Costello, Cao, Gelcich, Cisneros-Mata, Free and Froehlich2020). The idea of a blue revolution reliant on mariculture instead of wild stocks is gaining traction, especially as capture fisheries peaked at the end of the 20th century (Pauly & Zeller, Reference Pauly and Zeller2016).
Conservation aquaculture
Conservation aquaculture, defined as ‘the use of human cultivation of an aquatic organism for the planned management and protection of a natural resource’ (Froehlich et al., Reference Froehlich, Gentry and Halpern2017, p. 1), is a strategy to help replenish natural populations. Here we include two categories of culture that could be considered conservation aquaculture: stock enhancement and restoration aquaculture. We define stock enhancement as releasing cultured individuals to supplement the populations of exploited species that face continued high fishing pressure, and restoration aquaculture as releasing cultured individuals to rebuild historically exploited populations of species that are now protected and face minimal fishing pressure.
The intentional release of cultured organisms into the ocean for stock enhancement dates from the early 1800s, with mixed positive and negative impacts on ecosystems, species and economic systems (reviewed by Kitada, Reference Kitada2018). Increasingly rigorous principles for responsible stock enhancement have been developed (Blankenship & Leber, Reference Blankenship and Leber1995) and improved (Lorenzen et al., Reference Lorenzen, Leber and Blankenship2010). Guiding principles include grounding practices in basic knowledge of the species and fishery to facilitate realistic enhancement that is evaluated through scientific monitoring and assessment (Lorenzen et al., Reference Lorenzen, Leber and Blankenship2010). However, the global review of Kitada (Reference Kitada2018) revealed that stock enhancement remains experimental for the majority of species and ecosystems. Furthermore, empirical assessments are typically missing and when present show a trend towards both ecological and economic failure (Kitada, Reference Kitada2018). For example, integrating stock enhancement with metapopulation modelling to create a self-sustaining reserve network for cultured shellfish, such as oyster, reveals the challenges of rebuilding an ecosystem, even when enhanced sites show clear demographic benefits within their boundaries (Puckett & Eggleston, Reference Puckett and Eggleston2016). Ecosystem condition is typically more important than aquaculture release (Kitada et al., Reference Kitada, Nakajima, Hamasaki, Shishidou, Waples and Kishino2019); thus, rebuilding habitats and effective controls on harvest should be in place prior to restoration aquaculture.
Restoration aquaculture aims to improve a damaged or diminished ecosystem, and its implementation in marine systems is typically for revitalizing foundational species (e.g. ecosystem engineers) for bottom-up benefits. These efforts are currently being employed on salt marsh, oyster reefs, seagrass, mangrove, kelp forest and coral reef habitats (Duarte et al., Reference Duarte, Agusti, Barbier, Britten, Castilla and Gattuso2020). Coral restoration efforts blending culture and outplanting approaches have demonstrated some success; for example, outplanted coral populations in Japan have been observed spawning (Zayasu & Shinzato, Reference Zayasu and Shinzato2016).
In some cases, natural populations have been reduced to such a low level that restoration aquaculture may be the only means to prevent extinction (Anders, Reference Anders1998). Targeted enhancement of endangered species using conservation aquaculture remains problematic in marine ecosystems because of constraints on financial and technical resources, and degraded environments. Therefore, it is typically the action of last resort. For example, following the cessation of fishing in the 1990s, white abalone Haliotis sorenseni were expected to go extinct within 10 years without intervention (Hobday et al., Reference Hobday, Tegner and Hacker2001; NOAA, 2001). A restoration aquaculture programme took 19 years to rear, release into the wild, and monitor cultured white abalone juveniles (Rogers-Bennett et al., Reference Rogers-Bennett, Aquilino, Catton, Kawana, Walker and Ashlock2016). Likewise, time, money and effort has gone into the culturing of pinto abalone Haliotis kamtschatkana, with only 10% survival one-year post release (Carson et al., Reference Carson, Morin, Bouma, Ulrich and Sizemore2019; Dimond et al., Reference Dimond, Bouma, Carson, Gavery, O'Brien, Simchick and Sowul2022).
Importantly, stock enhancement and restoration aquaculture are typically posited as conservation strategies, but both become necessary because of failed management at local and international levels. Therefore, the industrial application of aquaculture as a fisheries solution has been recognized as a distraction from addressing the proximate causes of decline, typically poor management practices and degraded habitats (Meffe, Reference Meffe1992). Before implementation of new aquaculture outplanting programmes, techniques need to be established based on data from studies of long-term survival, functional equivalency, cost-effectiveness, and estimates of the impact on livelihoods and food security (Lorenzen et al., Reference Lorenzen, Leber and Blankenship2010). The uncertainty of success and cost of conservation aquaculture make the protection and management of wild populations critical, ideally before species approach a point at which further drastic intervention strategies are needed such as closing fisheries or restricting trade. However, conservation aquaculture still receives considerable attention and support as a means of repopulation despite the many well-documented barriers to successful in situ implementation (Glazer & Delgado, Reference Glazer, Delgado and Aldana Aranda2003).
Queen conch in decline
The queen conch, Aliger (formerly Lobatus, Eustrombus or Strombus) gigas, is a large herbivorous marine snail that was once common throughout the Caribbean, but populations have been greatly reduced by overharvest (Vaz et al., Reference Vaz, Karnauskas, Paris, Doerr, Hill and Horn2022). Queen conch primarily disperse during a pelagic larval phase and can potentially travel great distances (Vaz et al., Reference Vaz, Karnauskas, Paris, Doerr, Hill and Horn2022; reviewed by Stoner et al., Reference Stoner, Davis and Kough2023). Conch populations exhibit genetic isolation related to oceanic distance; thus, a careful blend of local and regional management is required to ensure connectivity among stocks (Truelove et al., Reference Truelove, Box, Aiken, Blythe-Mallett, Boman and Booker2017). After settlement, queen conchs spend c. 1 year buried as infauna during the day to avoid predation until they are big enough at c. 2 years of age (10 cm in length) to avoid fish gape limits (Iversen et al., Reference Iversen, Jory and Bannerot1986, Reference Iversen, Bannerot and Jory1990). Older individuals inhabit a variety of relatively shallow ecosystems, including seagrass, hardbottom and rubble, from where they are typically harvested by hand, using freediving or compressed air diving. Research on complex reproductive (reviewed by Stoner & Appeldoorn, Reference Stoner and Appeldoorn2022) and benthic recruitment ecology (reviewed by Stoner, Reference Stoner2003) demonstrates that the species requires minimum densities to maintain population fitness. Maintaining high abundances of a species that is relatively easy to exploit is a challenge for conch fisheries management (Prada et al., Reference Prada, Appeldoorn, van Eijs and Pérez2017). The decline in the queen conch abundance has been well documented as the species plays an important role in the lifestyle, heritage and economy of countries within its range, including The Bahamas where the consensus of fishers is that the population is decreasing (Kough et al., Reference Kough, Belak, Paris, Lundy, Cronin and Gnanalingam2019). Despite decades of protection in Florida, USA, populations have been slow to recover from heavy exploitation and are hindered by depensatory breeding effects because low adult density inhibits spawning (Delgado & Glazer, Reference Delgado and Glazer2020). The metapopulation structure of the queen conch has become fragmented as abundance has diminished (Vaz et al., Reference Vaz, Karnauskas, Paris, Doerr, Hill and Horn2022), which further hinders replenishment because larval sources become scarce and recruitment sporadic or eliminated by high fishing pressure (Kough et al., Reference Kough, Belak, Paris, Lundy, Cronin and Gnanalingam2019).
The queen conch is included on CITES Appendix II and international trade is regulated (Prada et al., Reference Prada, Appeldoorn, van Eijs and Pérez2017). Although the species has not yet been assessed for the IUCN Red List, it was protected as a threatened species under the US Endangered Species Act in 2024 (NOAA, 2024). In some countries, conch exports have been banned, fisheries have been closed, are no longer viable or are increasingly at risk of failing (Stoner et al., Reference Stoner, Davis and Kough2019). The long-term ecological consequences of removing a major herbivore such as the queen conch from Caribbean marine ecosystems remain unknown (Tewfik, Reference Tewfik2014); thus, strategies that reverse the trajectory of decline are of great interest for both fisheries and conservation.
Queen conch aquaculture reviewed
Since the early 1980s, considerable efforts have been made to raise juveniles from queen conch egg masses in captivity (Davis & Cassar, Reference Davis and Cassar2020), leading to many attempts to supply animals for food and for restocking. These aquaculture accomplishments have been reported by the media as a tool for the restoration and rebuilding of declining queen conch populations (Supplementary Table 1).
A majority of the inhabitants of the small island nations where the queen conch is harvested and where aquaculture has been proposed for rebuilding conch populations rely upon local and international media sources for scientific knowledge, rather than peer-reviewed research papers. Media monitoring services are designed for businesses or marketing and public relations professionals to analyse published content from media outlets, including online and print news, broadcasts and podcasts. Meltwater (Meltwater News US Inc., Chicago, USA) is a media monitoring service that scans more than 270,000 sources for user input keywords to aggregate content. For this study, we used Meltwater Services to compile articles that contained the keywords ‘queen conch’ AND (‘aquaculture’ OR ‘hatchery’ OR ‘nursery’ OR ‘farm’) and that were published during 1 January 2013–31 May 2024. Reported media coverage was vetted to ensure that each individual story featured queen conch aquaculture and not the keywords dispersed across unrelated content. Travel-centric articles that featured visits to the Turks and Caicos Conch Farm were treated separately (Supplementary Table 2). Each individual article was reviewed for accuracy, and quotes were retained that promoted aquaculture as a viable method to repopulate the queen conch. The resulting database of unique articles is provided in Supplementary Table 1 and summarized in Table 1.
Table 1 Queen conch Aliger gigas aquaculture featured in the media during 1 January 2013–31 May 2024. Unique articles are media pieces that we located using Meltwater Services (Meltwater News US Inc., Chicago, USA) and total placements are these articles featured in media outlets. The sum of unique articles that suggested that queen conch aquaculture can rebuild conch populations in each year was tabulated using adjectives that describe aquaculture's effect on conch populations. Quotes are from representative articles; Supplementary Table 1 contains sources and quotes from each unique article. Reach was calculated by Meltwater Services and is the estimated number of people exposed to media outlets that placed stories.
1 1 January–31 May 2024.
In the majority of unique stories, queen conch aquaculture is reported as a tool to rebuild populations (Table 1). The most common descriptive effect of aquaculture upon queen conch populations was to ‘restore’ (19 unique articles; Table 1) by ‘releasing’ (eight unique articles; Table 1) cultured individuals. However, despite decades of experimentation, neither commercial nor conservation aquaculture has proven successful for field repopulation, as comprehensively reviewed by Stoner (Reference Stoner2019).
The largest hurdle to conservation aquaculture of the queen conch remains the high natural mortality rate (> 95% annually) in natural juvenile nurseries and outplant areas (Stoner, Reference Stoner2019). Attempts to increase survival rates by raising animals for a longer duration so that they reach larger sizes before release are constrained by the increased costs of specialized feed and decreased viability of the cultured animals as defects accumulate and fitness is reduced (Stoner & Glazer, Reference Stoner and Glazer1998; Stoner, Reference Stoner2019). Aquacultured animals exhibit physical features that make them more vulnerable once they are outplanted into an unprotected, natural setting, including decreased shell strength, mass and spine growth (Stoner, Reference Stoner2019). Additionally, conch exhibit behavioural deficits, including a decreased propensity to burrow, low anti-predator responses and an inability to identify proper foods (Stoner, Reference Stoner2019). Survival is further modulated by the challenges of locating appropriate outplanting sites, providing available nursery habitat, identifying the proper release time, and controlling density-dependent effects on growth and predation (Stoner, Reference Stoner2019). However, even when the release site and season are optimized, mortality remains high (Stoner, Reference Stoner2019). Despite efforts to maximize their likelihood, high survival rates remain unlikely.
Challenges
The low rates of survival from post-settlement to near maturity, when viewed alongside large-scale fishery extraction and low aquaculture production, emphasize that with current techniques it is neither commercially feasible to replace wild harvest nor ecologically feasible to restore queen conch populations using conservation aquaculture. Both stock enhancement and restoration aquaculture remain inviable for the queen conch based on ecological and economic constraints. The following examples use estimates of demographic rates from the literature and fisheries data from recent reports to illustrate the formidable challenges faced by queen conch conservation aquaculture.
Juvenile production required to replace a single adult
A primary goal of conservation aquaculture for the queen conch, spanning both restoration and stock enhancement, is to release cultured juveniles to produce reproductively viable adult queen conchs. New, pioneering approaches allow juveniles to be grown from egg-masses anywhere in the Caribbean using mobile hatcheries powered by solar energy (Davis & Cassar, Reference Davis and Cassar2020). These small-scale hatcheries can be operated in remote areas and can generate 2,000 juveniles per year (Davis & Cassar, Reference Davis and Cassar2020), although hatcheries require access to egg masses typically collected from the wild. Laboratory culture of the queen conch has become routine, resulting in increased interest in the idea that it could be used for restoration and stock recovery (Supplementary Table 1). However, small-scale culture does not currently produce an ecologically meaningful quantity of juveniles for outplanting. Using a conservative estimate of 95% annual mortality in juvenile conch, from the compiled results of nine peer-reviewed studies (Stoner, Reference Stoner2019) and from an age-structured mortality model (Appeldoorn, Reference Appeldoorn1993), 4,000–10,000 juveniles need to be released to result in a single animal reaching its earliest possible maturity at 4 years of age (Stoner & Appeldoorn, Reference Stoner and Appeldoorn2022; Fig. 1).
Fig. 1 Estimating survivorship to maturity from releasing cultured queen conch Aliger gigas. Conservative estimates of natural mortality from in situ experimentation (Stoner, Reference Stoner2019) and a stage-based model (Appeldoorn, Reference Appeldoorn1993) demonstrate the time and number of young, in cultured batches (Davis & Cassar, Reference Davis and Cassar2020), required to replace a single, sexually mature queen conch.
Stock enhancement to replace commercial landings
Despite steep declines in queen conch stocks, there are still active queen conch fisheries, ranging from small-scale to those supporting large exports. In other species, conservation aquaculture to enhance wild stocks has been applied to improve fisheries while allowing natural populations to rebound by offsetting part or all of the wild catch with aquaculture-sourced individuals (Free et al., Reference Free, Cabral, Froehlich, Battista, Ojea and O'Reilly2022). In 2019, some of the largest fisheries for the queen conch were in Nicaragua and Honduras (Horn et al., Reference Horn, Karnauskas, Doerr, Miller, Neuman and Hill2022), with export quotas of 419 and 638 t of 100% clean queen conch meat, respectively. Such quotas involved retrieval of an estimated 6,972,210 individuals from the Nicaraguan Rise, a relatively shallow bank stretching north-east from the Central American coast towards Jamaica. If an aquaculture programme is designed to enhance wild stocks by annually supplementing the Nicaraguan Rise population with just 10% of the exported adult catch, it would require an approximate production of 2,788,884,000 juveniles, as a conservative estimate. This estimate uses the assumption that 4,000 outplants generate one adult in 4 years, and a conservative average of seven adults generating 1 kg of meat (Fig. 1). The yield of meat is based on fishery reports that 6.6 adults generate 1 kg of 100% clean meat on the Nicaraguan Rise (Ehrhardt & Galo, Reference Ehrhardt and Galo2005) and that 8.14 adults generate 1 kg of 50% clean meat on the Pedro Bank (Ehrhardt et al., Reference Ehrhardt, Tewfik, Smickle and Black2023). There remains a lack of documented success in small-scale or industrial population restoration, and scaling up production to commercial levels remains unlikely, with an unknown, yet high, economic cost (Fig. 2).
Fig. 2 Fishery value and the aquaculture production to partially offset landings in one region. Nicaragua and Honduras have lucrative queen conch fisheries on the Nicaraguan Rise, with values estimated in USD. Converting cultured animals into a fishery product, clean meat, requires time and a considerable outplanting effort. Based on an estimate of required sexually mature adults to generate the catch in 2019, replacing just 10% of the legally allowed harvest would require approximately 2.8 billion outplanted individuals from aquaculture. The costs to create and maintain the infrastructure to generate this level of culture are unknown, but probably vastly exceed the value of the fishery from both countries.
Potential production from protecting wild populations
There are still actively breeding populations of the queen conch that support small and large populations and fisheries throughout their natural range that, if protected, have the potential to generate a vast quantity of eggs and larvae (Fig. 3). Importantly, the queen conch exhibits density-dependent breeding (reviewed by Stoner & Appeldoorn, Reference Stoner and Appeldoorn2022), so fishery managers and scientists have recommended a minimum spawning density of 100 individuals per ha (FAO, 2020). To succeed, stock enhancement and restoration aquaculture must sustain localized population densities at that level while accounting for fishery extraction and/or natural mortality. The average individual age in a breeding population of the queen conch, including disproportionately important large, mature and highly fecund individuals (Froese, Reference Froese2004), is significantly greater than 4 years old (Boman et al., Reference Boman, Graaf, Nagelkerke, Stoner, Bissada and Avila-Poveda2018; Tewfik et al., Reference Tewfik, Babcock, Appeldoorn and Gibson2019; Stoner & Appeldoorn, Reference Stoner and Appeldoorn2022). Therefore, our estimate of juvenile outplants required to replace an adult in a breeding aggregation is an underestimate.
Fig. 3 Natural yield of the queen conch from protecting wild breeding populations. An area of 1 km2 could support 10,000 adults at the recommended minimum density for reproduction. The minimum observed annual reproductive output of 5,000 females is 15.5 billion eggs (Stoner & Appeldoorn, Reference Stoner and Appeldoorn2022) which leads to an estimated 155,000 settled conch after accounting for planktonic mortality to achieve life-time replacement. Rates were estimated for a population at full capacity and without the added mortality of harvest, making them conservative.
Aquaculture decreases planktonic mortality yet even with planktonic mortality estimates accounted for, natural reproduction outstrips foreseeable aquaculture production levels (Fig. 3). Mortality rates during larval dispersal are unknown for the queen conch and for most other marine species with a bipartite lifecycle and planktonic larval phase (Houde & Bartsch, Reference Houde, Bartsch, North, Gallego and Petitgas2008), but they far exceed those of settled juveniles. Statistical models to estimate larval mortality require extensive field sampling and typically focus on quantifying either predation or growth rates but can use size-structured approaches that combine the two (Hinchliffe et al., Reference Hinchliffe, Pepin, Suthers and Falster2021). Here, natural mortality is estimated from hatching to settlement based on the lifetime fecundity calculated by Stoner & Appeldoorn (Reference Stoner and Appeldoorn2022) and the assumption that mortality rates enable replacement. Our examples (Figs. 1–3) are conservative with regards to natural mortality, harvest estimates and potential industry growth. An added benefit of protecting swathes of mature, reproductively active gastropods is increased population resilience and faster recovery when confronted with climate change or other events that cause mass mortality (Micheli et al., Reference Micheli, Saenz-Arroyo, Greenley, Vazquez, Espinoza Montes and Rossetto2012).
Discussion
Queen conch conservation aquaculture, designed to restore natural populations or partially offset harvest, faces substantial hurdles that science, non-profit entities and industry have yet to overcome. Furthermore, a changing environment with increased frequency of extreme storms causing negative effects on infrastructure is another barrier to broadscale aquaculture that has impacted past commercial operations (Wida, Reference Wida2018). However, queen conch aquaculture remains a critical tool in education and tourism and has contributed to understanding queen conch biology and ecology. Queen conch aquaculture should be encouraged as a means of furthering scientific knowledge and increasing community support while simultaneously and transparently communicating its current limitations for repopulation efforts.
Conservation benefits of aquaculture
Queen conch aquaculture is widely perceived as a positive and successful scientific practice (Table 1). People who enjoy consuming or celebrating the conch throughout the Caribbean benefit from understanding the lifecycle and the staggering mortality experienced as they grow towards maturity. Small-scale aquaculture facilities and mobile labs make larval transport and slow growth tangible concepts for educators, students and the general public. For example, the Turks and Caicos Queen Conch Farm, a commercial enterprise, was an effective educational attraction for tourists (Supplementary Table 2). Small-scale farms and hatcheries also provide an opportunity for community involvement and could partially incentivize a decrease in fishing pressure by paying fishers to participate in conservation programmes rather than in harvesting. Aquaculture has also answered important questions about larval hatching, development, metamorphosis, swimming capacities and food consumption (Stoner et al., Reference Stoner, Davis and Kough2023). The spatial management and conservation of the queen conch has also been shaped by contributions from aquaculture that facilitate connectivity and demographic modelling across their range (Vaz et al., Reference Vaz, Karnauskas, Paris, Doerr, Hill and Horn2022; Stoner et al., Reference Stoner, Davis and Kough2023). Future research on the impact of stressors such as climate change and disease could use cultured individuals so as not to impact wild stock.
There are many longstanding research needs before aquaculture can contribute effectively to in situ restoration and conservation. Overall, evaluating the plausibility of restoration aquaculture for the queen conch requires a large-scale experiment across multiple locations that tracks free-ranging individuals from release through to maturity, to gauge mortality, realized population enhancement and the potential benefits across the ecosystem. It is imperative that an interdisciplinary team of aquaculture practitioners, ecologists and local stakeholders, including fishers, design and conduct these experiments to fully evaluate and substantiate success prior to proposing aquaculture as a realistic and scalable avenue for population recovery.
Fisheries management
Policy changes have been successfully used to rebuild queen conch populations across many spatial and temporal scales. Over small spatial scales, no-take protected areas can harbour breeding populations (Stoner et al., Reference Stoner, Davis and Booker2012; Kough et al., Reference Kough, Cronin, Skubel, Belak and Stoner2017; Tewfik et al., Reference Tewfik, Babcock, Appeldoorn and Gibson2019) that replenish unprotected areas, as predicted by biophysical models (Kough et al., Reference Kough, Belak, Paris, Lundy, Cronin and Gnanalingam2019) and confirmed empirically (Kough, Reference Kough2024). At the country scale, in Jamaica, scientific surveys and genomic connectivity studies (Blythe-Mallett et al., Reference Blythe-Mallett, Aiken, Segura-Garcia, Truelove, Webber and Roye2021) coupled with adaptive fishery management over the course of several decades (Ehrhardt et al., Reference Ehrhardt, Tewfik, Smickle and Black2023) led to a sustainable seafood certification by the Marine Stewardship Council in 2024. For severely overexploited populations, the management strategy of last resort is a full fishery closure coupled with protection. In Florida, USA, these measures resulted in a protracted recovery from < 30,000 adult queen conch in 1986, to 200,000 in 1990 (Berg & Glazer, Reference Berg and Glazer1995), and an estimated 700,000 in 2017 (Florida Fish and Wildlife Conservation Commission, unpubl. data).
Community action, such as starting a queen conch nursery or citizen scientist surveys, may instil conservation ethos. Should active intervention beyond policy be deemed necessary, translocations to increase adult densities above minimum thresholds for reproduction have been posited as an alternative to aquaculture (Delgado et al., Reference Delgado, Bartels, Glazer, Brown-Peterson and McCarthy2004; Delgado & Glazer, Reference Delgado and Glazer2007). Translocating queen conchs from larval sinks to larval sources to boost reproductive output can provide an inexpensive, genetically sound alternative to aquaculture as hatchery production costs are eliminated. Translocations maintain the genetic integrity of the stock because of the use of wild animals as opposed to releasing hatchery-reared juveniles potentially derived from few parents (i.e. there is no outbreeding depression). Lastly, translocations will have a more immediate impact on reproductive output because there is no need to wait for juveniles to survive to reproductive maturity. Experimental-scale translocations have shown that translocated queen conchs engage in reproductive activities at their new location (Delgado et al., Reference Delgado, Bartels, Glazer, Brown-Peterson and McCarthy2004) and do not displace native individuals within the aggregation (Delgado & Glazer, Reference Delgado and Glazer2007). However, a cautious approach must be taken to ensure that the carrying capacity of the habitat is not exceeded and that larval sinks and sources are correctly identified.
The way forward
Queen conch aquaculture has been practiced with success in laboratories and hatcheries around the Caribbean, yet there is so far no scientifically quantified or documented example of successful repopulation of wild stocks with cultured conchs. A well-documented example of an ecologically viable, self-replenishing population that supplements or replaces traditional wild capture would promote its practicality for responsible stock enhancement. Furthermore, such an example would increase confidence in restoration aquaculture as a solution to prevent extinction should the conch population plummet and fisheries close. This has been recognized, and for as long as conchs have been cultured, attempts have been made to replenish wild populations. Overcoming natural mortality rates remains a challenge. Four decades ago in Puerto Rico, Appeldoorn & Ballantine (Reference Appeldoorn and Ballantine1983) suggested that fisheries enhancement through aquaculture was untenable without reducing juvenile mortality rates. In 1998, after more than a decade of experimental hatchery releases in the Florida Keys and The Bahamas, Stoner & Glazer (Reference Stoner and Glazer1998) came to the same conclusion. The Florida Keys hatchery was the only well-documented attempt to assess the feasibility of using hatchery-raised juveniles to replenish wild stocks. When the Florida hatchery closed, a cost–benefit analysis showed that it was not economically feasible to replenish wild stocks with hatchery-raised juveniles because of high mortality rates and the exorbitant monetary costs of compensating for mortality (Glazer & Delgado, Reference Glazer, Delgado and Aldana Aranda2003). The largest and most well-funded aquaculture facility for the queen conch was the Caicos Conch Farm. This commercial endeavour closed because of poor profitability (Trade Wind Industries, Reference Trade Wind Industries2018) compounded by a hurricane strike (Wida, Reference Wida2018), highlighting the financial challenge of stock enhancement. Although progress continues, poor conch survival (Figs. 1–3) and the history of past attempts (reviewed by Stoner, Reference Stoner2019) suggest a cautionary approach for presenting culture as a viable tool for queen conch repopulation without further advances. The creation and implementation of agreements for species management and restoration can be fraught with challenges, as illustrated by those for migratory fish (Cullis-Suzuki & Pauly, Reference Cullis-Suzuki and Pauly2010), yet the best hope for species recovery remains better management of remaining wild stocks at national and international levels, informed by fisheries science and emphasizing protected area management and sustainable fishing approaches (Froese, Reference Froese2004).
The idea that the conservation aquaculture of the queen conch is an option to replenish populations provides an appealing excuse to avoid the difficult tasks of managing local capture fisheries and addressing the causes of degraded ecosystems. An inclusive and interdisciplinary approach to restoration is needed to ensure the conservation of healthy habitats. Depending on repopulation through aquaculture in lieu of the robust management of natural resources is not in the best interest of the future of the species nor the people and industries that rely upon it.
Author contributions
Writing and revision: all authors; data for examples: RA, NE; illustrations: SM; media review: KG; coordination: AK, AS.
Acknowledgements
This research received no specific grant from any funding agency, or commercial or not-for-profit sectors. The text benefited from comments from C. Knapp, J. Sigwart and two anonymous reviewers.
Conflicts of interest
None.
Ethical standards
No specific approval was required to assemble this work, which abided by the Oryx guidelines on ethical standards.
Data availability
This study combines previously published data from reviews and industry.
Open access
