UBC Theses and Dissertations
The queen conch fishery of Belize : an assessment of the resource, harvest sector and management Strasdine, Susan Anne
The primary goal of this study was to evaluate potential management options for the conch (Strombus gigas) fishery of Belize based on biological analyses of the present fishery. The specific objectives were to: 1) assess the condition of the stock; 2) estimate the possible yield of the resource; and 3) recommend viable alternatives for management. Information on population dynamics of Strombus gigas was obtained largely from the literature. A yield-per-recruit analysis was conducted to gain an understanding of how changes in the age of entry into the fishery and mortality and growth rates effect yield. Historical records on landings and fishing effort obtained from the fishing cooperatives were analyzed to assess the state of the stock. Landings-per-unit-effort was calculated in a manner unique to the quantity and quality of data available. The structure of the current management system, operations of the fishing cooperatives and routines of fishermen were also considered in the final evaluation of viable management options. Conch was first exported by Belize around 1950 but the fishery remained small until 1967. Exports then climbed dramatically from 174,000 kg in 1967 to 562,634 kg in 1972. During the remainder of the 1970's, production declined due to a decline in stock biomass and subsequently, effort. Typical of all exploited populations, biomass decreased as the abundance of older adults declined and the size distribution of the catch shifted toward smaller individuals. The modification of harvest rate thereafter is believed to be an operational response of the fleet to a mixed species resource. As the relative abundance, market value and distribution of lobster, conch and scale fish change, fishermen alter their harvesting strategy in order to maximize their economic returns per trip. By the 1980*s, the conch fishery was essentially seasonal with roughly one third of the year's total production being delivered within the first month (October) of the nine season. Size limits and a closed season were implemented in 1978 and the size of meats landed at the fishing cooperatives increased from an average of 66 gm in 1976 to 131 gm in 1985. Fishing effort for conch rose from 1980 to 1984 due to an increase in the absolute number of conch divers and remained high in 1985 and 1986. Landings per man-day (md) varied little between 1978 and 1984; average landings-per-unit-effort (LPUE) over this period (15.0 kg/md) was one third the LPUE of the late 1960's. However, in 1985 and 1986 LPUE dropped dramatically; a consequence most likely of recruitment variability and/or growth overfishing in intensely fished areas. The current minimum limit on shell length (17.8 cm) is less than the predicted size of first capture at which yield-per-recruit is maximized (i.e., 21.7 cm shell length; 113 gm marketed meat weight). Present regulations also allow fishermen to harvest conch before they are capable of reproducing. It is recommended that more stringent measures be taken to reduce the possibility of recruitment overfishing until a more thorough assessment of the resource can be made. Improvements regarding the collection of data necessary for stock assessment are suggested. The management options considered most appropriate for the conch fishery of Belize at present include, in order of importance: size limits, season closures and gear restrictions. A regulation prohibiting the harvest of nonlipped individuals would be most effective in protecting the breeding population. However, this measure is difficult to enforce because conch are cleaned at sea. Hence, a minimum size restriction on market-cleaned meats corresponding to the average meat yield of adults (120 gm; 4.2 oz) is suggested as well. Maintaining the current 3-month closed season and prohibition on harvesting using SCUBA offers additional protection in that these restrictions reduce the chances that fishermen will harvest spawning adults and adults which have migrated into deep-water refuges.