Damage assessment and survival estimates in the wedge clam (Donax trunculus) caught by mechanical dredging in the northern Alboran Sea

Abstract

ABSTRACT This paper describes the impact of dredging on populations of the wedge clam (Donax trunculus) at two sites along the northern Alboran coast. Damage was assessed by quantifying shell and foot damage on commercial clams caught with mechanical dredges. Survival experiments were carried out to assess their survival capacity after 24 h purification treatment and 72 h cold storage, which represents an issue of great interest for fisheries research, management and marketing. Overall, 2.4% of wedge clams suffered any type of damage, including chipped edges and scratched valves. Higher proportions of shell-damaged individuals were positively correlated to bottom features (e.g. gravel content in sediment). Moreover, higher towing speed significantly increased shell damage. Analyses of shell damage areas revealed that the anterior dorsal and ventral parts of the shell are the most vulnerable to dredging. A total of 15.9% of individuals showed damage on the foot, which seems not to affect their survival. The incidence of foot damage was mostly linked to sublethal predation, reflected in a positive correlation between the proportion of foot-damaged individuals and biomass of decapod crustaceans in the fishing ground. Finally, D. trunculus exhibited very low mortality rates after 24 h purification treatment (0.2–0.4%) and 72 h cold storage (0.3–3.2%). The survival rate at the end of the experiment was high (>96%), with the highest mortality observed 96 h after the fishing day. No correlations were found between mortality rates and bottom type or towing speed.