Influence of mesh size and tooth spacing on the proportion of damaged organisms in the catches of the Portuguese clam dredge fishery

Experiments to assess the effect of mesh size and tooth spacing on the catch of Spisula solida were undertaken with the aim of determining an optimal combination of these two characteristics to minimize the dredging impact on by-catch species. However, our data showed that tooth spacing, mesh size and the interactions between these two factors did not affect the number of damaged macrofaunal individual's caught. This may be because infauna entered the dredge without passing through the space between the teeth and the mesh of the net bag closed as it was stretched by the weight of the contents, preventing the escape of the caught individuals. Thus, independently of mesh size, when the dredge is towed over the sediment, the retained individuals were injured due to abrasion between animals and/or between animals and debris. The severity of injuries inflicted by dredging on different macrobenthic species is related to their morphology and fragility.