Causes of shell scarring in dog cockles Glycymeris glycymeris L.

Experimental studies were conducted to investigate the possible causes of shell scars in the bivalve mollusc Glycymeris glycymeris, including fishing disturbance, predator attacks and burrowing activity. Individuals collected from an area of sea bed experimentally fished once by a scallop dredge 12 months previously did not display significantly more shell scars than those collected before fishing or from a control area. In the laboratory, Glycymeris offered to the predatory crab Cancer pagurus had a significantly higher incidence of scars seen in acetate peels of shell cross-sections than control shells. However, scarring on Glycymeris excavated from the sediment and left to reburrow was not significantly different from those in an undisturbed control group. Currently, it is not possible in G. glycymeris to differentiate between scars caused by fishing disturbance or natural disturbances, either on the grounds of visual appearance or position of damage.