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Helping to Sustain a Way of Life in the Bahamas

WHERE WE WORK

Exuma Cays 2011

A Comparative Study of Queen Conch Populations Inside and Outside of a Marine Reserve and Reproductive Biology

Areas near Lee Stocking Island in the Exuma Cays, and within the Exuma Cays Land and Sea Park, near Warderick Wells were revisited by Community Conch during the summer of 2011 in order to replicate surveys completed by Dr. Allan Stoner in the early 1990′s. A reproductive biology study was also undertaken primarily to determine the relationship between lip thickness and reproductive readiness of queen conch in The Bahamas. The results of this work may prove to be very important in future management decision-making of queen conch stocks in the Caribbean region.

Objectives

Field work conducted by Community Conch during 2011 in the Exuma Cays had three principal goals:

  • To compare queen conch stocks near Warderick Wells (WW) in the center of the Exuma Cays Land and Sea Park (ECLSP) (protected from fishing) and near Lee Stocking Island (LSI) (fished area) with surveys made during the early 1990’s
  • To compare reproductive behavior of queen conch near WW, LSI, and the commercial fishing grounds near south Andros Island and at the southern edge of the Berry Islands
  • To explore relationships between conch size and shell lip thickness (an index of age) and their reproductive maturity.

Findings

  • The density of queen conch has declined more than 90% in the deeper waters of the fishing grounds near Lee Stocking Island since surveys were initially conducted in the early 1990′s. The density of adult conch in the shallow bank water near LSI remained very low. The average lip thickness of adults near LSI had decreased indicating a younger population overall, a typical sign of overfishing.
  • Within the ECLSP, a significant decline (69%) in adult density was found in shallow bank waters, though density of the deeper water population remained relatively high. The average lip thickness of all adults in the ECLSP increased, indicating an aging population and declining recruitment within the Park boundaries.
  • Mating was virtually non-existent near LSI, with observation of only 3 mating pairs during 2 weeks of daily field surveys.Within the ECLSP, reproduction was still high with observed mating frequency of nearly 10% of adults on the shelf reproductive grounds, compared to frequencies found on the fishing grounds of the Berry Islands (5.9%) and Andros (2.4%).
  • Analysis of gonad tissues showed that most male conch do not reach sexual maturity until their shell lip thickness reaches 10 mm (more than 3/8 inch). Most females were not sexually mature until shell lip thickness was 15 mm (more than 1/2 inch). These new findings, coupled with known growth rates of the shell flare, indicate that conch do not reproduce for at least one year after the shell lip begins to form.

Conclusions and Recommendations

  • Conch densities are decreasing in commercially fished areas to levels that will not sustain the populations. Fishing grounds in the Berry Islands, Andros Island and near Lee Stocking Island all show evidence for collapsing populations.
  • Conch densities at Warderick Wells have decreased 69% on the shallow bank and 35% overall during the last two decades. Although the Park protects existing conch, there is not sufficient recruitment from outside the protected area to maintain conch populations within the Park, and further decline is expected without changes in fishery management policies, especially reduced harvest.
  • Experience in Florida and other Caribbean regions shows that recovery of conch populations is very slow after they fall below those thresholds. Releases of hatchery-reared conch in Florida, Mexico, Puerto Rico, and The Bahamas have not been successful in rebuilding stocks, and natural populations and population structures need to be conserved.
  • Queen conch populations are rapidly declining below the critical thresholds for reproduction. Given the results of our study of reproductive biology, it is likely that the majority of conch now harvested in The Bahamas are indeed immature and have not reproduced. An amendment to harvest size regulations is needed.
  • A single marine reserve such as the Exuma Cays Land and Sea Park, in isolation cannot indefinitely conserve a species subject to heavy fishing in the surrounding waters. A network of reserves and substantially reduced fishing mortality will be required for sustainable harvest of queen conch in The Bahamas.