Determination of mortality in exploited freshwater pearl mussel (Margaritifera margaritifera) populations

Estimates of mortality, based on relative numbers of live mussels and empty shells observed were obtained for a sample of seven exploited Scottish freshwater pearl mussel (Margaritifera margaritifera) populations. Total mortality (Z) estimates ranged from 0.058 to 0.189 year−1 and fishing mortality (F) estimates ranged from 0.005 to 0.129 year−1. General trends of increasing Z and F with age were apparent. Pearl fishers generally targeted larger, older mussels. In one heavily exploited population, the Z and F estimates converged, indicating that most of the mortality in older mussels (>50 years) was due to the effects of destructive pearl fishing. Since a complete ban on pearl fishing was introduced in 1998, illegal pearl fishing has continued albeit at a reduced level.