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 11^th 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 Fisheries



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 13^th 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.

posterior

anterior

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

1.3.3.1 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).

1.3.3.2 Juvenile Strombus gigas

Young Queen Conch (S. gigas