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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 Apri- mary goal of conservation aquaculture for the queen conch, spanning both restoration and stock enhancement, is to re- lease cultured juveniles to produce reproductively viable adult queen conchs. New, pioneering approaches allow ju- veniles to be grown from egg-masses anywhere in the Caribbean using mobile hatcheries powered by solar energy (Davis & Cassar, 2020). These small-scale hatcheries can be operated in remote areas and can generate 2,000 juveniles per year (Davis&Cassar, 2020), 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 re- sults of nine peer-reviewed studies (Stoner, 2019)and from an age-structured mortality model (Appeldoorn, 1993), 4,000–10,000 juveniles need to be released to result in a sin- gle animal reaching its earliest possible maturity at 4 years of age (Stoner & Appeldoorn, 2022; Fig. 1).
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 im- prove fisheries while allowing natural populations to re- bound by offsetting part or all of the wild catch with aquaculture-sourced individuals (Free et al., 2022). In 2019, some of the largest fisheries for the queen conch were in Nicaragua and Honduras (Horn et al., 2022), with export quotas of 419 and 638 tof 100% clean queen conch
meat, respectively. Such quotas involved retrieval of an esti- mated 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 approx- imate production of 2,788,884,000 juveniles, as a conser- vative estimate. This estimate uses the assumption that 4,000 outplants generate one adult in 4 years, and a conser- vative 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, 2005) and that 8.14 adults generate 1 kg of 50%clean meat on the Pedro Bank (Ehrhardt et al., 2023). There remains a lack of documented success in small-scale or industrial population restoration, and scaling up pro- duction to commercial levels remains unlikely, with an unknown, yet high, economic cost (Fig. 2).
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, 2022), so fishery managers and scientists have recom- mended 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 dispro- portionately important large, mature and highly fecund in- dividuals (Froese, 2004), is significantly greater than 4 years old (Boman et al., 2018; Tewfik et al., 2019; Stoner & Appeldoorn, 2022). Therefore, our estimate of juvenile out- plants required to replace an adult in a breeding aggregation is an underestimate.
FIG. 1 Estimating survivorship to maturity from releasing cultured queen conch Aliger gigas. Conservative estimates of natural mortality from in situ experimentation (Stoner, 2019) and a stage-based model (Appeldoorn, 1993) demonstrate the time and number of young, in cultured batches (Davis & Cassar, 2020), required to replace a single, sexually mature queen conch.
Oryx, 2024, 58(6), 700–709 © The Author(s), 2025. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324001443
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