Browsing by Author "Arnold, William S."
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- Rebuilding viable spawner patches of the overfished Spisula solida (Mollusca : Bivalvia): a preliminary contribution to fishery sustainabilityPublication . Joaquim, Sandra; Gaspar, Miguel; Matias, Domitilia; Ben-Hamadou, Radhouan; Arnold, William S.Populations of commercially important bivalves along the coast of Portugal are depleted as a consequence of natural and anthropogenic causes. A pilot experiment was designed to determine the feasibility of transplanting individuals from natural clam beds to a closed fishing area in an effort to rebuild relatively high-density patches of Spisula solida. For this purpose, clams were equally partitioned into two groups (undersize and legal clams) and transplanted at a density of 40 clams m(-2) into two areas 50 m(2). Transplanted and control clams were sampled to estimate survival, condition index, biochemical composition, and reproductive condition. Generally, the physiological condition of clams was not affected by the method of transplanting. One year after transplanting, survival was 45%. The increase in local abundance of mature clams should facilitate successful fertilization and increase the residual reproductive value of each clam relative to its pre-transplant value. Transplanting undersize clams may be more advantageous because they are more likely to spawn at least once before harvest. The experiments demonstrate that spawner transplants may strengthen S. solida populations and can be used in stock-enhancement programmes which, in conjunction with effective management measures, can contribute to the sustainability of the S. solida fishery.
- Reproductive activity and biochemical composition of the pullet carpet shell Venerupis senegalensis (Gmelin, 1791) (Mollusca: Bivalvia) from Ria de Aveiro (northwestern coast of Portugal)Publication . Joaquim, Sandra; Matias, Domitília; Matias, Ana Margarete; Moura, Paula; Arnold, William S.; Chícharo, Luís; Baptista Gaspar, MiguelThe present study characterizes the reproductive cycle of Venerupis senegalensis (=V. pullastra) from Ria de Aveiro (Portugal) as well as its nutrient storage and exploitation strategy. The reproductive cycle followed a seasonal cycle that correlated negatively with sea surface temperature, and comprised a ripe stage in winter followed by a spawning period that began in late winter and ended in the early summer. This extended spawning may be an advantageous strategy for the species because it ensures a continuous supply of settlers. Gametogenesis began in late summer/early autumn and intensified with the decrease in temperature during autumn. The condition index increased even during the spawning period, which indicates that there is rapid recovery and that reserves are accumulated during late summer and used later in the gametogenic process. Proteins did not contribute significantly to gametogenesis and the glycogen pattern is typical of conservative species, since gametogenesis depends largely on the amount of glycogen stored. The lipid storage and utilization cycle showed that gametogenesis took place in autumn/winter and that energy reserves were accumulated in summer.