The influence of commercial harvesting on parasite infection in the bivalve Austrovenus stutchburyi

Abstract

Commercial harvesting often reduces densities of target species, potentially affecting transmission of parasites within the population. Rates of parasitic infection not only impact the hosts directly, but can result in wider ecosystem effects through influences on host behaviour. Commercial harvesting may therefore have important ecological consequences beyond the direct effects of removal of biomass. Clams (Austrovenus stutchburyi) are commonly infected by trematode parasites (Acanthoparyphium spp. and Curtuteria australis) and have been commercially harvested in Otago, New Zealand, since 1983. To assess the effects of harvesting on the abundance of trematodes in A. stutchburyi, the number of parasites per clam was compared in harvested and unharvested areas. The mean number of parasites per clam was 36% higher at commercially harvested sites, suggesting that harvesting enhances the local transmission of parasites. Harvesters may be able to reduce their influence on parasite infection levels in clam populations by harvesting less intensively and allowing more time between harvests for clam biomass to regenerate.