Rebuilding viable spawner patches of the overfished Spisula solida (Mollusca: Bivalvia): a preliminary contribution to fishery sustainability

Sandra Joaquim,Miguel B Gaspar,William S Arnold,Domitília Matias,Radhouan Ben-Hamadou

doi:10.1093/icesjms/fsm167

Abstract

AbstractJoaquim, S., Gaspar, M. B., Matias, D., Ben-Hamadou, R., and Arnold, W. S. 2008. Rebuilding viable spawner patches of the overfished Spisula solida (Mollusca: Bivalvia): a preliminary contribution to fishery sustainability. – ICES Journal of Marine Science, 65: 60–64. 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 m2. 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.

Highlights

Many bivalve stocks around the world have collapsed as a consequence of a combination of commercial fishing effort, recreational and commercial watercraft activities, recruitment failure, mass mortality, and habitat degradation (Arnold, 2001)
After transplanting, most clams had burrowed into the sediment
The success of any restoration effort may be site-specific and will likely depend on the same factors that contributed to the population decline originally (Arnold et al, 2005; Bell et al, 2005)

Summary

Introduction

Many bivalve stocks around the world have collapsed as a consequence of a combination of commercial fishing effort, recreational and commercial watercraft activities, recruitment failure, mass mortality, and habitat degradation (Arnold, 2001). These impacts affect potential fishery yields, and may compromise the productive potential of ecosystems. On the other hand, when the natural supply of juveniles fails to reach the carrying capacity of the habitat, recruitment may be inadequate to increase the productivity of an operational fishery This situation can be redressed if stock rebuilding effort is implemented to augment the biomass of spawning adults (Bell et al, 2005; Lorenzen, 2005)

Methods

Results

Conclusion