The conch abundance indicator gives the number of queen conch (Strombus gigus) adults per unit area.This unusual shelled animal has cultural, commercial, and ecological significance in the region. It is protected to some extent by international conservation measures.
The number of adult conchs on a reef reveals a great deal about long-term prospects for the local population—which may in turn have important implications for populations in other areas. Densities lower than 50 conchs/hectare have been found to result in reproductive failure;7 recent studies indicate that the critical threshold for reproductive success may be as high as 200 conchs/ha.8
Long-term survival of this important herbivore depends on:
- Limited fishing, including no-fishing replenishment
zones - Habitat protection, especially of nursery grounds
- Transboundary management that recognizes and
protects the animals’ early-life dispersal phase
Because queen conch could become threatened with extinction unless its trade is strictly regulated,9 CITES10 permits, which require that stocks be stable and sustainably managed, must be issued for all exports
We recommend that queen conch be monitored through regionally standardized systematic counts and targeted process studies (for example, studies of reproduction and dispersal), inside and outside MPA11 boundaries. Assessing conch abundance is usually relatively simple and inexpensive. Collecting data on larval dispersal is more challenging but is essential for understanding the effects of management
actions.
Fully protected MPAs are an effective tool for managing conch populations. Many marine animals produce larvae that float great distances before settling down to mature, but conch larvae are thought to stay a bit closer to home during their fairly short larval phase. A network of MPAs with areas closed to conch fishing will help replenish populations throughout the region.
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A promising sign of Benchmark reef recovery would be 50-300 conchs/ha, with narrower ranges to be eventually defined according to habitat and management zone.
- The status of queen conch varies widely throughout
the region. Most abundance data come from MPAs,
which are expected to have higher densities than
areas outside MPAs. - Over the past 30 years, conch populations
and catches in many areas have been declining
due to overexploitation, illegal harvesting of
undersized animals, and a lack of transboundary
management. - Conch numbers, which are highly responsive
to protection measures, have made a significant
comeback in areas where fishing has been
limited or prohibited.12 In some no-take or highly
restricted quota areas, numbers have rebounded
to Benchmark or even Target levels.