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Chapter 1. Introduction
1.1 Strombus gigas, A Threatened But Protected Species
65 species of Strombidae are still in existence and the majority of those are found in the Indo-Pacific Oceans (ConchNews). 6 species of Strombidae are found throughout the Caribbean and Florida oceans (McCarthy, 2007): S. alatus, S. costatus, S. gallus, S. gigas, S. pugilis, and S. raninus, one of which, Strombus gigas, known as the Queen Conch, has highest commercial fisheries value of the six species and is commercially threatened. In 1990 the parties to the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region (Cartagena Convention) included S. gigas in Annex II of its Protocol Concerning Specially Protected Areas and Wildlife (SPAW Protocol) as a species that may be used on a rational and sustainable basis and that requires protective measures (NOAA). Consequently on 11th June 1992 the United States listed S. gigas under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), Appendix II; classified as commercially threatened (Theile, 2005). S. gigas then became the first large-scale fisheries product regulated by CITES (NOAA). This requires countries to harvest at a sustainable rate before they can obtain a permit to export (Thiele, 2001).
The SPAW Protocol and CITES treaties are generally a positive step for the species, assisting efforts to ensure use and trade of S. gigas, however this is largely a commercial move and should not be confused with meaning it is officially on the endangered/threatened species list. S. gigas is simply on a list of species, fauna and flora not yet threatened or endangered, but with legal commitment by the governments to prevent them becoming so by implementing plans for management by establishment of closed seasons and regulation of their harvest and trade (Thiele, 2005). The Caribbean Fishery Management Council supports a regional International Queen Conch initiative, to promote a common international management strategy for the sustainable use of S resources in the Caribbean region, by making recommendations to address specific issues. E.g. International Queen Conch Initiatives (FAO 2003). In January 1991, 12 of the 14 Governments of the Caribbean Community officially launched the CARICOM Fisheries Resource Assessment and Management Programme (CFRAMP) to promote sustainable use and conservation of the fisheries resources, setting up the 1994 Lobster and Conch Resource Assessment Unit to provide data on conch and lobster resources in the Caribbean (Haughton 2004).
Fig 1.1 The wider Caribbean region showing hypothetical Exclusive Economic Zones of countries – those of CARICOM countries are shaded grey (Haughton, 2004).
1.2 Commercial Importance – History Of Queen Conch Fisheriesâ€¨â€¨
S. gigas, have been harvested by Caribbean fishermen for centuries (Stoner 1997), in some regions old conch shell middens show conch have been fished for over 1400 years (Torres, 2002) – used for religious ceremonies, for trade and ornamentation, and a source of protein from its meat. Fishing pressure, previously entirely small-scale local fisheries on surrounding islands, has now developed into a large commercial trade commodity with an important fishery resource in the Caribbean area and increasing international demand for the rare meat (Berg & Olsen 1989). Outside of the live meat trade, S. gigas is also known for its pearls and shells, sold by locals and tradesmen to tourist as souvenirs as a by-product of conch meat harvest.
The increase in intensive fishing pressure caused by its rising commercial value since the 1970’s (Cochrane et al 1996) has caused queen conch populations to decline throughout their distribution range (Stoner, 1997; Theile, 2005). This is largely due to the slow maturation growth to harvest size of 3-4 years (Davis) ensuring S. gigas are unable to offset the development of fisheries technical enhancements allowing them to fish larger quantities and at previously unobtainable depths (Wells 1989). The use of scuba and hookah gear from 1984 has now become widespread and due to the depletion of near-shore shallow water stocks because of overfishing, former deep-water refugia (>20 m) is now increasingly accessible and subject to the same intense exploitation (CFMC/CFRAMP, 1999), shifting fishing efforts from near-shore to offshore areas in parts of the Bahamas, Colombia, Mexico, Haiti and the Dominican Republic (CITES, AC19 Doc. 8.3 2003). In 1986, the U.S. banned all fishing of Strombus gigas populations instead importing approx. 80% of world trade, >1,000t year-1 (NOAA 2003), from Caribbean Islands. The majority of S. gigas populations the U.S are importing from have continued to decline. CITES reviews, following species listing in 1992, report population densities in some areas to be so low that recruitment failure is a risk to local fisheries in parts of Belize, Colombia, the Dominican Republic, Haiti, Honduras, Panama, Puerto Rico and the Virgin Islands with stock collapses and resulting in total or temporary closure of the fishery in Bermuda, Cuba, Colombia, Florida, Mexico, the Netherlands Antilles, the Virgin Islands and Venezuela (CITES AC19, Doc. 8.3 2003). The primary cause for the population decline is widely demonstrated to be commercial trade overfishing (Stoner, 1994) but Stoner (1994) implies habitat degradation may be a secondary factor, especially in the shallow water nursery habitats of seagrass meadows, which are crucial to Strombus gigas sustainability. There are still some larger areas that still maintain stable populations, – the Bahamas (Stoner & Ray, 1996), Jamaica (Stoner & Schwarte 1994) and the Turks and Caicos Islands due to hatchery replacement (Bene & Tewfik, 2001) as well as smaller areas of St. Lucia, St Vincent and Virgin Islands (taken from Table 1, p76 Cochrane, 1996).
The significant trade review undertaken in 1995, at the 13th meeting of the Animals Committee, formulated recommendations in 1997 requiring states to prove conformity to CITES and slowly by March 1999 most states had conformed. By 2005 Antigua and Barbuda, Barbados, Bahamas, Belize, Colombia, Cuba, Dominica, Dominican Republic, Honduras, Nicaragua, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, and Trinidad and Tobago had been removed from the Review of Significant Trade of S. gigas (CITES SC54 Doc. 42, 2006). However, CITES recognizes that despite being registered for over 10 years stock declines continue to occur (Notification No. 2006/055, 2006) and in 2006 the Animals Committee concluded that trade was of urgent concern in 3 range states and of possible concern in a further 13 (CITES SC54 Doc. 42, 2006). The important exporting countries of Haiti and Grenada have released no information and with low adult densities reported from fishing all exports from these states have been suspended as they may currently being exploited at rates that may be unsustainable (CITES AC22 Doc. 10.1). The National Marine Fisheries Service support the CITES embargo on queen conch imports (NOAA, 2003) which will remain until evidence is provided that the CITES recommendations have been implemented (Thiele, 2001).
1.3 Biology of Strombus gigas
Strombus gigas are large, soft-bodied, marine shelled gastropod molluscs. They have a thin layer of tissues between the body and the shell, a mantle, which creates a hard external spiral-shaped shell up to 30 cm in length from calcium carbonate extracted from the seawater and sediments. This outer shell develops the distinctive pink coloured flared lip that easily identifies the species and is why the shell also has a horny periostracum coating to deter predators.
The body is divided into the head, the visceral mass, and the foot.
Fig 1.2 Adult female conch without her shell (FWRI, 2006)
The conch head has a pair of tentacles tipped with light-sensitive eyestalks and a long proboscis radula that has thousands of tiny denticle protrusions for feeding. The foot, at the posterior, is a pointed, sickle-shaped, hardened operculum tip used to propel forward in a unique type of hopping locomotion commonly referred to as “stromboid leap propulsion”. This enables escape from predators by breaking up their scent trail (FWRI, 2006). They have a siphonal canal with an indentation near the anterior end called a stromboid notch. (Hyman 1967, Abbott 1974 quoted http://bellsouthpwp.net/c/u/culpsb/conchnews/strombidae).
1.3.1 Ecology of Strombus gigas
Strombus gigas inhabits the neotropical Atlantic waters of Bermuda, southern Floridian and Mexican coasts of Central America in the Gulf of Mexico Caribbean Sea region, and off the South America coasts of Venezuela and Brazil. Strombus gigas are herbivorous, grazing primarily on algae, grasses, and floating organic debris and are consequently usually found in warm, shallow, clear, subtidal water of oceanic or near-oceanic salinities settled on sandy substrates, in rocky habitats, on coral reefs or coral rubble sea floors amongst seagrass and algae (McCarthy, 2007; Cochrane, 1996). Strombus gigas can be found in discrete aggregations up to hundreds or thousands of individuals who actively select these preferable habitats (Stoner, 1997). Adult S. gigas are typically found at depths less than 100 meters concentrated in water 10- 30 meters deep due to the photosynthetic light requirements of algae and plant growth (Randall 1964). Predators of the Queen Conch are known to be around 130 marine species including various species of mollusc, lobster, turtles, crabs, sharks, rays, snappers and Nassau Grouper, (Coulston, 1987; Culp and Stoner 1999; CITES AC19 Doc 8.3; Culp et al, 1997). As a defence they bury into the sand to hide, unprotected/unburied conch being less likely to survive (Coulston 1987). Conchs burying behaviours show wide variations, possibly related to environmental conditions of water temp – conch increase burying in cooler winter period (Appeldoorn 1985) – and wind/sea conditions – conch are more active at high tide as a response to increased predator activity in the upper intertidal zone (). The increased amount of attached organisms on the shell of older conch suggests a decrease in long-term burying activity with increases in conch size (Iverson et al, 1986).
1.3.2 Conch Reproduction
In the wild, adult queen conch maintain a 1:1 sex ratio in an undisturbed population (Cochrane, 1996), and sexual maturity for males and females occurs by approximately between 3.5 and 5 years, usually when the flared lip is greater than approximately 0.5 cm thick (Appeldoorn, 1988b; Berg and Olsen, 1989). Onset of sexual maturity varies within and between different Strombus gigas populations depending on their site specific habitat quality, food availability and water depth all changing growth rates (Martin-Mora et al., 1995), with faster growth rates inducing earlier maturation (Berg, 1976). Queen conch are dioecious (McCarthy, 2007), fertilization is internal when the male inserts a verge into the female’s siphonal notch, the female retaining the male sperm till fertilisation during the process of laying eggs (McCarty, 2007). The seasonal reproductive period increases copulation as a linear function of bottom water temperature the summer months (Stoner et al. 1992). Water quality, food supply, a 12-hour photoperiod, and temperature limitations all negatively affect individual female pairing, copulation, and egg-laying reproduction causing a decrease in egg masses (Stoner 1992; Shawl 2004). Females lay demersal egg masses in long continuous strands up to 50 to 75 feet long containing 185,000 to 460,000 eggs in each strand (Shawl & Davis 1994). These are deposited in requirement sand substrate (Shawl & Davies 2004) at an average rate of 1.5m hr-1, completing in less than a day (Randall 1964). Spawning can multiple times during an egg-laying season, the length of which varies depending on geographic location (Stoner?), but lasts typically 6 – 8 months usually between March and October (TABLE ?) with stimuli other than temperature, such as declining photoperiod, inducing the end of reproductive activity (Stoner et al, 1992)
1.3.3 Life Cycle of Queen Conch
Fig 1. 3 Life cycle of the Queen Conch, Strombus gigas
220.127.116.11 Migration and Dispersal
The life cycle of Strombus gigas begins by embryonic development that proceeds rapidly, dependent on temperature, after the fertilization of spawning reaching the gastrula stage after 16 hours. The pelagic larvae emerge within 72 hours – 5/6 days after spawning (Cochrane 1996). This is also influenced by temperature and by the presence of phytoplankton (Stoner, 1997). By around 12 days they are lobed, free-swimming veligers, found in open water up to 100 meters deep, localised in above the thermocline, where they drift over 18-40 days in the currents of the upper layers feeding on the plankton (Posada and Appeldoorn, 1994; Stoner, 1997). During this period long distance transport by surface currents to deeper water areas (Iversen, et. al 1990) can occur up to 900km (Davis et al., 1993).
Larvae then descend, 17 to 22 days after hatching, settling into the adult benthic habitats, when induced by settling cues of substrate (Boettcher and Targett 1996) and location. Larvae then require an environmental stimulus to induce metamorphose response such as the presence of specific algae foods Laurencia poitei and the epiphyte Fosliella spp. found on Thalassia testudinum (Davis, 1994) usually associated within site substratum and sediment (Davis and Stoner, 1994). Metamorphosis is usually within five days of settlement, unique in developmental history as the competence period is shorter than the precompetence period, instead of equal to or longer than the precompetence period. They are competent for only 6 days at 28 to 30°C, losing this ability if the required conditions within the habitat cannot be met (Davis and Stoner, 1994). Short-term competence is ordinarily associated with metamorphosis to a broad spectrum of cues and this explains the conch response to a variety of benthic cues found in juvenile conch seagrass habitats (Davis 1994). The larvae reach metamorphosis between 25 and 29 days turning lobes into feet while the proboscis develops to about 0.2 cm in length developing a small transparent shell within 24 hours called a protoconch (James & Wood). Again development shows environmental variation for example larvae of March, April, May, and September have slower development than the larvae of June, July and August. The survival at settlement averaged 30±5.18% with highest survival June and July with 38±6.30%, lowest March (22±7.22%) and September (20±7.02%) (Brito-Manzano & Aldana Aranda, 2004).
18.104.22.168 Juvenile Strombus gigas
Young Queen Conch (
22.214.171.124 Conch Morphology
Conch shell growth is deterministic; from approx. 3 years conch stops increasing in shell length, growing only by thickening of the shell, particularly the flared lip that it starts producing. At sexual maturity, which occurs at approximately 3 years (Berg 1976) and lasts approximately 7-10 months (Glazer and Berg, 1992), lip flare growth initiates (Appledoorn 1988). Both growth directions occur simultaneously until adult shell length is reached (Appledoorn 1988). Measuring shell lengths is the most accurate method to date juveniles – estimates for mean shell length range from approx. 10.8cm for a 1-year old animal, 17cm for a 2-years old animal, and 20.5cm for +3years (Berg, 1976). In adults shell lip thickness increase has been used to estimate growth from maturation in years (Appeldoorn, 1988a, 1990). This is only a relative measure as the deterministic growth affects estimates of juvenile growth and therefore accurate aging, and mortality (CFMC/CFRAMP, 1999). The shell length of adult S. gigas can decrease by bioerosion of the shell on substrate types, and interior volume of the shell can shrink with age inducing significantly smaller body size (CFMC/CFRAMP, 1999), both factors hindering accurate aging.
Extreme spatial variation occurs in shell size of different S. gigas populations. Factors affecting shell size include site habitat quality, food availability and quality and water depth (Martin-Mora et al., 1995), which coupled with the presence of predators and increased depth are all thought to slow juvenile and adult conch morphometric growth. Growth rate is positively correlated to final shell length, indicated by slower growing conch tending to reach smaller final shell lengths and greater age at maturation (Alcolado, 1976). Increased predation can cause weaker, thicker or denser/heavier shells with shorter spines (Delgado et al. 2002; Stoner & Davis, 1994), and increasing depth causes tighter coiling of the shell resulting in a wider, thicker shells and fewer, longer spines (Alcolado, 1976, quoted in McCarthy, 2007).
Conch travel up to 100 yards per day, mostly at night migrating for two reasons: Firstly, a long-lived ontogenetic migration movement of larger juveniles leaving nursery areas moving into deeper water (Stoner et al. 1988), in the direction of the seasonally synchronous tidal currents, increasing in conch density with the passage of the migration. This serves as a density-dependent or habitat-dependant dispersal mechanism for juvenile conchs from centres of recruitment (Stoner et al. 1988). The second reason is a summer migration of adults inshore to shallower water grass beds for spawning (Appledoorn 1993). This begins when temperatures start to increase (Stoner and Standt 1992; Coulston 1987) and the conch return offshore to sand or algae habitat and deeper water. Conch have also been observed to move to deeper water with age (Stoner, 1997).
1.3.5 Natural Mortality of Strombus gigas
The Queen Conch is a relatively slow-growing long-lived species, reaching a maximum longevity of between 20 & 30 years with an average of 26. In deeper water this can be extended to 40 years (NOAA). Appeldoorn (1988) derived a relationship between age and natural mortality that exponentially decreases until the conch reaches sexual maturity (Appeldoorn, 1988). Mortality along with most other morphometric and maturity data also varies seasonally, due to habitat, predation and food limitation (Stoner and Glazer, 1998) but natural mortality of S. gigas has not been accurately quantified due to bioerosion of the shell by substrate (CITES AC19 Doc 8.3, 2003), and it is thought that aging any S. gigas specimen greater than 10 years old should be considered is unreliable, and therefore the complete lifespan of queen conch is unknown (SEDAR, 2007).
1.4 The Biological/Ecological Importance of Strombus gigas
Strombus gigas is an important member of marine benthic and macrofauna communities in seagrass meadows. As a hebrivory mollusc, S. gigas regulates the abundance of seagrass detritus and algal blooms of bottom-dwelling algae such as Batophora oerstedi, performing a visual ‘cleaning’ of the sediment surface from the normal light brown colour to white, clearing filamentous algae and small detrital particles (Stoner et al., 1995). By decreasing significantly the standing crop of biomass of dead or detritus remains of senescent seagrass blades, seagrass epiphytes, macrodetritus and macroalgae, without reducing living seagrass biomass, S. gigas grazing, similar to other important marine herbivory grazers such as Diadema, potentially stimulates rates of primary production of algae, macrophytes, seagrasses and the role of below ground nutrient reserves (Valentine, 1999). In comparison, S. gigas grazing on epiphytes and detritus could adversely influence other components of the benthic community such as amphipods and other smaller Mollusca invertebrates, which are dependent upon detritus for food or cover, reduced in numbers by S. gigas grazing. S. gigas must therefore play a major role in the trophic flux of the tropical seagrass community. Over-exploitation may cause significant ecological changes, including an increase in small grazers or rapid accumulation of organic matter in the sediments and trophic cascade changes that may reduce productivity and limit recruitment of S. gigas and all other species (Klumpp, et al 1992.).
1.5 Future Outlook and Conservation – Conserving Reproductive Stocks
Having ascertained as above, that conch are important to the ecosystem, the CITES inclusion highlighted global concerns, although mainly for the fisheries economy rather than ecological importance. With this well-documented decline of S. gigas that led to the CITES inclusion, research programs were developed designed to monitor conch stock and to determine how best to rehabilitate the depleted population. Attempts at researching methods to halt the decline and preserve the species have been focusing on both preserving the current stocks of native S. gigas specimens and maintaining stocks by ensuring reproduction or transplanting hatchery reared juveniles into the wild. Increasing interest in preserving the natural global stock led to a focused account of conch reproduction, potential mariculture hatcheries and maintenance of the species as a successful fisheries economy. However, to maintain any mariculture or fishery a strong healthy stock of native conch will need to be conserved. Two methods to protect and preserve high densities of native adult queen conch are at the forefront of conservation of the fisheries economy: depth refugia and marine reserves (Stoner, 1997).
1.5.1 Depth Refugia
As S. gigas are herbivorous, predominantly found in well-lighted photosynthetic algal regions of shallow sub tidal zones 10-30m deep. The majority of S. gigas are therefore accessible to scuba divers driving the maximum abundance of adult conch to greater depth. Numbers at depths are generally very low (Stoner, 1997) and in response to declining shallow water population’s one potential form of management for maintaining a healthy reproductive native population is to limit fishing to free diving (Posada & Garcfa-Moliner, 1996). Relatively natural populations of adult conch are, in comparison, uncommon in depths <10 m showing the highest abundance at depth beyond the reach of free-diving conch fisherman. The limit would allow the survival of these small, deepwater "refuge" populations, ensuring some reproduction to replenish the regional stocks (). A possible problem is that because the vast majority of queen conch spends their first 2-3 years in shallow water, migrating when mature from bank nursery sites into deeper water, those on the bank in the fished area may be harvested before reaching water sufficiently deep to protect them from free-diving fishermen (). Also young adults and adults that do not migrate to deep water are then all accessible to free divers; the intense fishing for conch in shallow water could ultimately reduce deep-water refuge stocks ().
1.5.2 Marine Protected Areas (MPA’s)
Protected marine areas provide an alternative technique already employed to maintaining high densities of adult conch. Marine Protected Areas (MPA’s) are the globally designated marine specific protected sites, and are used as a management tool for limiting the ecosystem effects of fishing, including the biological and socio-economic aspects. Although increasing, currently only an estimated 0.6% of the world’s oceans are designated MPA’s, the largest being the Great Barrier Reef, however many of the largest can be found in the Caribbean oceans. UNEP-WCMC, 2002, defined MPA’s as “any area of the intertidal or subtidal terrain, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment”. The MPA’sprotect all species and rare habitats or nursing grounds in that environment, which can include historical features such as shipwrecks, and cultural sites of interest (such as known whale routes). MPA’s aim to protect their environment according to area and species, by restricting access, mining and fishing practices, and by prioritising preservation and conservation. In extreme cases tourism is restricted, use of certain boats, and ultrasound are either banned or restricted in the conservation areas.
126.96.36.199 Does Marine Protection work? – Ecological Effects of MPA’s
There is sufficient evidence that fishing negatively affects ecosystems (Sumaila, et al, 2000) and to reduce fishing is the main principle of fishery model predictions. Models predict that the establishment of MPAs, in particular, for overexploited commercial populations, can reduce negative effects of fishing consequently maintaining local economies, and livelihoods of fishermen (Behnken, 1993). Reserve protection ensuring a natural source of maintaining species diversity for the future, creating an ecological success and benefiting sustainability of future fisheries economies, as well as rehabilitate those that have collapsed (Halpern, 2003). The scientific consensus is that, marine reserves, on average, regardless of their size, and with exceptions, result in long-lasting significantly higher density, biomass, individual size, and diversity (Lubchenco et al, 2000) when evaluated for both overall communities and by each functional group within these communities (carnivorous fishes, herbivorous fishes, planktivorous fishes/invertebrate eaters, and invertebrates) within reserves as opposed to outside the reserve (or after reserve establishment vs. before) (Halpern, 2003) and often rapid increases in the abundance, and productivity of marine organisms. By providing refuge nursery areas protecting resident species and heritage protection of important habitats such as coral, MPA’s increase density of species and decrease mortality, habitat destruction and any indirect ecosystem effects. On average, research provides evidence that creating a reserve can raise mean organism size, double density, (nearly) triple biomass, and increase diversity of communities by 20-30% relative to the values for unprotected areas (Halper, 2003) and Halpern deems the results to be robust despite the many potential sources of error in the individual studies with considerable variance (Halpern, 2003). Outside reserve boundaries the few studies that have examined spill over effects (Lubchenco et al, 2000), but the increase in density and diversity of marine life, is predicted to increase reproduction potential and by permanently eliminating fishing practices, change the ecosystem from disturbed to mature (Sumaila et al, 2000) restoring community structure (McClanahan and Obura, 1995). Outside of the reserve there is potential for the abundance of exploited species to also increase in areas adjacent to reserves via regionally larval export replenishing populations (Lubechncho et al, 2000).
188.8.131.52 Strombus gigas Specific MPA Restrictions – Do they Work?
Long-lived slow growing epibenthic species and those requiring highly structured habitat would be expected to thrive in the MPA albeit a long process rebuilding the habitat structure (Watling and Norse, 1998). For S. gigas, the establishment of marine reserves is theoretically the best way to allow populations to recover (Stoner 1997) as from a single-species point of view, MPA are designed to restore populations to pre-industrial fishing levels by reducing the probability of extinction for marine species resident within them by using fishing restrictions (Lubchenco et al, 2000). Invertebrate density trends as shown by other species and functional groups, imply diversity will be higher inside reserves but so far invertebrate biomass has been documented lower within reserves (Halpern, 2003). Indirectly the reserve may however affect numbers of S. gigas predatory fishes, and for invertebrate biomass in particular, the effectiveness depends on its position in the localised food chain. Currently there are few S. gigas specific evaluation of the biological impact of a reserve on the stock of queen conch, the first conducted in the Turks and Caicos islands (Bene & Tewfick, 2003), followed by (Stoner and Ray, 1996) comparing the density of adult queen conch in the 1984 Restricted Exuma Cays Land and Sea Park and in the fished area near Lee Stocking Island, Exuma Cays. Both studies showed increased densities of S. gigas in the reserve as shown in Table 1, Bene’s results showing density 6 times higher within the reserve and S. gigas shell length significantly smaller in the reserve than in the fished areas describing the existence of a crowding effect (high density induced reduction in growth rate) within the reserve (Bene & Tewfik, 2003) hypothesized due to a) reduced fishing mortality following creation of reserve b) existence of natural barriers that impede emigration of adults to outside the reserve. (Stoner, 1997) concluded that marine reserves can conserve spawners indicated by juvenile conch numbers increasing in Exuma Park and that the increased larval production within the reserve transporting downstream to areas of fished populations (Stoner, 1997).
Table 1. Density of adult queen conch in the Exurna Cays Land and Sea Park near the island of Waderick Wells and in the fished area near Lee Stocking Island, Exuma Cays. (mean + SE for each depth interval). (Stoner & Ray, (1996)
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