Aspects of the biology, ecology and fishery of the beaked clam Eumarcia paupercula (Holten, 1802), in Maputo Bay
Clam populations globally have declined, or been depleted, with one of the major causes being uncontrolled human exploitation. This thesis investigates the population structure, growth, reproduction and exploitation of the beaked clam Eumarcia paupercula in Maputo Bay. The substantial commercial harvesting of this clam may lead to overexploitation of the resource. In this regard, some fundamental knowledge is necessary for the management of future exploitation. The data collection was based on an 18-months (November 2012 - April 2014) sampling for population structure across a tidal flat. The growth analysis was performed on FiSAT II, using mark-recapture experiments and length-frequency data. Monthly reproduction analysis was based on the fluctuation of body weight and gonad smear analysis. Furthermore, interviews were used to ascertain the importance of the resources for collectors and estimate landings of E. paupercula. The von Bertalanffy growth function and length-frequency analysis revealed that E. paupercula has a fast growth rate and a short life span. Eumarcia paupercula is a year-round spawner with higher peaks in the summer; recruitment follows a similar pattern, occurring over the year and after the spawning peaks. The clam collectors, the majority of whom are women, have experienced an increase in the effort required to collect clams, resulting in a decline of catches over the season. This study highlights that temporal population dynamics are influenced by collection and reproductive patterns, and that single environmental parameters do not explain the patterns of growth, reproductive cycles and spatial distribution. Findings of this study have relevance and application for the livelihood of the collectors, as well as the sustainability of the Eumarcia paupercula stock, by providing a basis for fishery governance. While recommendations are presented for the management of E. paupercula collection, the Ministry of Fishery in Mozambique also has to consider collecting data on bivalves, as they are an important source of income for artisanal fishers. Future research should include monitoring of a less exploited population, so as to understand better how collection impacts on the population dynamics of E. paupercula. Furthermore, laboratory studies of the larval cycle are necessary to gain thorough understanding of the species life cycle.
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