Effect of tooth spacing and mesh size on the catch of the Portuguese clam and razor clam dredge

M Gaspar

doi:10.1006/jmsc.1998.0423

Abstract

Experiments on the selectivity of the clam and razor clam dredges were carried out during July 1995, on the south coast of Portugal. The effects of mesh size and tooth spacing were investigated for both the clam and razor clam dredges. Four different mesh sizes (25, 35, 40, and 50 mm) and three different tooth spacings (15, 20, and 25 mm for the clams Spisula solida and Venus striatula, and 10, 15, and 20 mm for the razor clam Ensis siliqua) were used. The results indicated that the tooth spacing did not have an effect on the selectivity. The best mesh sizes were 40 mm for the clam fishery (S. solida and V. striatula) and 66 for the razor clam (E. siliqua). These mesh sizes will result in considerable reduction in the numbers of small- and medium-sized individuals in the catch.

Highlights

An important bivalve fishery takes place along the south coast of Portugal
A 50% selection length of approximately 25 mm was the target for the clam dredge because this value is the current minimum landing size for S. solida and V. striatula
Data from the present study suggests that the estimated L50% values are markedly below the stipulated minimum legal landing length (MLL) for S. solida and V. striatula

Summary

Introduction

An important bivalve fishery takes place along the south coast of Portugal. Among the Portuguese, bivalve fishing is an ancient and traditional activity. In ancient times bivalves were harvested by hand or by hand rakes at low tide. At the beginning of the twentieth century, small dredges were introduced to the fishery. The exploitation of bivalve ocean beds along the Portuguese coast is recent and was initiated in 1969 by the Spanish fleet under the auspices of the ‘‘Portuguese-Spanish Fishery Agreement’’. The Spanish fleet directed its fishing effort mainly towards two species Ensis siliqua and Venus striatula. The high economic value of these species in the external market soon aroused great interest in the Portuguese fleet. The fishing effort as well as the gear efficiency increased and as a consequence bivalve beds soon showed signs of depletion.

Methods

Results

Conclusion