Queen Conch, Strombus Gigas

SRAC Publication No. 7203 October 2005 Species Profile Queen Conch, Strombus gigas Megan Davis* The queen conch, Strombus gigas, Natural history This movement is thought to help is the largest molluscan gastropod the conch make a quick escape (shell length, SL, of 7 to 9 inches; The adult of this slow-moving from predators and also break up 18 to 23 cm) of the six conch mollusc has a heavy shell (5 its scent trail. The eyes are highly species found in the shallow sea- pounds; 2.3 kg) with spines on developed and are at the tips of grass beds of Florida, the each whorl of the spire and a two protruding stalks. At the base Bahamas, Bermuda, the glossy, deep pink, flared aperture of the eye stalks is a long pro- Caribbean Islands, and the north- (Fig. 1). The orange-yellow man- boscis used for grazing diatoms ern coasts of Central and South tle, located around the soft body and detritus from seagrass blades America. The queen conch is of the conch, secretes the shell. and sand grains. The hardened tip (the operculum) found in the territorial waters of Adult conch have separate sexes at least 36 countries and depen- at the end of the single, black- speckled foot propels the conch (Fig. 2) and are sexually mature at dent territories. It is known by about 4 years, after the lip has various names, such as caracol forward in a “hopping” motion referred to as a strombid leap. fully flared (Fig. 1). Conch are (Mexico, Honduras, Columbia), found at a 1:1 sex ratio in carrucho (Puerto Rico), cobo unfished populations. Queen (Cuba), and lambi (Hispaniola, conch form large spawning aggre- French Antilles). gations. Fertilization is internal. Many studies have focused on The typical 6- to 8-month egg-lay- fisheries management, ecology ing season is March to October, and culture techniques of S. with most activity occurring from gigas. In the mid-1970s, cultur- July to September when water ists began growing queen conch temperatures are the warmest (82 larvae to the juvenile stage for to 86 °F; 28 to 30 °C). The female stock enhancement and for grow- lays an average of nine egg mass- out markets as a way to offset es per season; each crescent- fishing pressure. The same cul- shaped egg mass contains approxi- ture techniques have been used mately 400,000 eggs (Fig. 3). The to study larval ecology and fish- thin, sticky strand of eggs is cov- eries oceanography, which con- ered with sand grains to camou- tribute to the development of flage it from predators during the regional fisheries management 3- to 4-day incubation period. plans. After the eggs hatch, the plank- totrophic veligers (larvae) drift in the water column for 2 to 8 Figure 1. Shell of an adult queen weeks, depending on phytoplank- conch, S. gigas (7 to 9 inches; 18 ton concentration, temperature, *Harbor Branch Oceanographic Institution, to 23 cm SL). (photograph by Tom and the proximity of settlement Aquaculture Division, Ft. Pierce, Florida. Smoyer) habitat. When the veligers are morphologically and physiologi- cally ready, they metamorphose into benthic animals in response to trophic cues from their seagrass juvenile habitat. Most conch nursery grounds are in seagrass meadows less than 20 feet (6 m) deep, where the seagrass density is 56 to 84 Thalassia shoots per square foot (600 to 900/m2). Juveniles have also been found in algal flats and on deep banks. The juveniles remain buried for most of their first year. As herbivorous gastropods, juveniles and adults feed on a variety of algae such as the green sea- weed Batophora oerstedi, or on detritus or diatoms commonly associated with the seagrass Thalassia testudinum. During the Figure 2. External sex organs of Strombus costatus (a) male and (b) female first couple of years, the juvenile milk conch, which are similar to those of S. gigas. (photograph by Tom conch grow longer shells (Fig. 4) Smoyer) and remain in the seagrass beds. Juveniles do not have flared lips and are sometimes referred to as rollers. As the flaring lip (Fig. 4) begins to form, the sub-adult conch migrate to deeper water near the reef tract and form spawning aggregations. Queen conch are estimated to have a life span of 25 years. Old conch have thick lips and are often called samba conch (Fig. 4). Fisheries and regulations For hundreds of years, queen conch have been harvested as a subsistence food source and the shells used for ship ballast, tribal tools, building materials, jewelry and decoration. Beginning in the 1970s, the queen conch commercial fishery developed in response to the rapid growth of tourism in the Caribbean and the increased international demand for the meat. Dishes such as conch frit- Figure 3. Queen conch, S. gigas, egg mass. (photograph by LeRoy Creswell) ters, chowder and salad are spe- cialties on menus throughout the region. Queen conch is consid- ered one of the most important weight of the animal, ranging range from $6.00 to $15.00 per benthic fisheries, second only to from 0.19 to 0.5 pounds (85 to pound and continue to increase spiny lobster. 228 g). The fisherman receives as conch stocks become more $1.00 to $3.00 per conch as a threatened. Shells, which are a Conch are typically fished using wholesale price. The conch meat by-product of the meat market, snorkel gear. Once landed on the is processed to remove the thick are sold as curios and souvenirs boat, the shells are removed and skin and the white meat is pack- in the U.S., Europe and the discarded onto shell piles called aged and frozen in 5-pound (2.3- Caribbean for $5.00 to $20.00 “middens.” The conch meat is kg) boxes. Retail prices for conch each. about 7 to 8 percent of the total the Turks and Caicos Islands, and USAID in Belize). In 1984, the first commercial conch farm was established in the Turks and Caicos Islands. Today, queen conch laboratories in Mexico (e.g., CINVESTAV-IPN) and Florida (e.g., Florida Fish and Wildlife Conservation Commis- sion, Harbor Branch Oceano- graphic Institution, and Mote Marine Laboratories) are con- ducting conch research and edu- cation programs. Culture techniques Broodstock and egg mass procurement Hatcheries must gather egg mass- Figure 4. Juvenile and adult S. gigas shells from 1 month old to 25 years old. es from the wild, which can be (photograph by Kathy Orr) an unreliable source. Therefore, an enclosed breeding site or “egg farm” is used to ensure a steady supply of wild egg masses for the The United States is the largest degradation may also be a factor, hatchery. A suitable egg farm site importer of conch from the especially the loss of important Caribbean and, in fact, imports nursery habitats close to shore. • is or was traditionally inhabit- approximately 78 percent of the In 1992, queen conch was listed ed by adult conch, conch meat in the international in CITES Appendix II and • has a calcareous sand and trade. About 1 million pounds became the first large-scale fish- coral rubble substrate with (458,000 kg) was imported in eries product to be regulated by low organic content, 2004, mostly from the Turks and CITES. All conch shipments Caicos Islands (Trade Database: must be accompanied by a • is located where water move- www.cites.org). Imports were as CITES permit stating that the ment is less than 1 knot, high as 4 to 5 million pounds in exporting country has deter- • is 4 to 8 m deep, and 2002 and 2003 when Honduras mined that the specimens have • is within 3 km of the hatchery and Dominican Republic con- been legally acquired and that facility, for ease of access and tributed more than 50 percent of the trade is sustainable. security. the supply to the U.S. In 2003, Some locations, including the CITES (Convention for the To retain the adult conch, the Bahamas, Puerto Rico and egg farm is enclosed with a rigid, International Trade of Endangered Florida, have established no-fish- Species of Wild Fauna and Flora) black polyethylene mesh (2 x ing zones or marine protected 2 inches; 5 x 5 cm) fence 1.6 to mandated a temporary closure of areas (MPA) to help conserve the the fisheries in these countries 3.3 feet (0.5 to 1.0 m) high. The queen conch and other ecologi- mesh is held perpendicular to until the stocks increase and a cally important species. These sustainable fisheries plan is put the substrate with reinforcing types of management efforts, rods and the ends are attached to into place. This multilateral envi- along with regional fisheries ronmental organization protects moorings, boulders or the land. It plans and enforcement, will help is not necessary to remove the and regulates species to ensure this important species recover. that international commercial fence during the nonbreeding trade does not threaten their sur- There is considerable interest in season unless it is in an area vival in the wild. the culture of the queen conch to where winter storms would dam- supplement dwindling natural age it. The depletion of conch stocks has populations. Research began in The egg farm should be stocked necessitated management regula- the 1970s in Los Roques, tions such as total fisheries clo- annually with sexually mature Venezuela, and in the 1980s sev- conch 1 month before the breed- sures (e.g., in Florida since 1986), eral labs in the region made sig- annual quotas, size regulations, ing season at a sex ratio of 1:1 nificant contributions to queen and a density of one conch per and the prohibition of scuba div- conch culture (e.g., University of ing.

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