CORRELATIONS BETWEEN HUMAN COLLECTING AND INTERTIDAL MOLLUSK POPULATIONS ON ROCKY SHORES

We tested whether the population structures of intertidal molluscs var ied with the activity of human collectors in northern Port Phillip Bay , Victoria, Australia We examined eight sites, two of which bad been p rotected for around 70 years by the area being used as a rifle range, with the other six being visited frequently by humans. The shores were examined in two different years, and in 1991 we counted humans and re corded their activities. At heavily visited shores, almost half of the people seen were simply walking while 25% were actively collecting de spite regulations prohibiting the collection of intertidal gastropods. The remaining people were fishing or skindiving. At the protected sho res, we observed only one collector and a handful of walkers over more than 20 observation periods, including weekdays, normal weekends, and holiday weekends. In 1989 and 1991, we compared size distributions of seven intertidal species between sites in the two categories. Four mo llusc species are taken for food and bait; the remaining three served as ''controls. '' The size distributions and abundance of noncollected species (Bembicium nanum, Lepsiella vinosa, and Cominella eburnea) di d not differ between visited and protected sites in either year althou gh most species did vary between individual sites. In contrast, three of the four collected species, Cellana tramoserica, Austrocochlea cons tricta, and Nerita atramentosa, were significantly larger at the prote cted sites, and N. atramentosa was markedly less abundant at heavily v isited sites. The fourth collected species, Turbo undulatus, has a dis tribution extending into the subtidal zone, and it is possible that in tertidal populations are replenished from deeper water. The changes in mean size of molluscs are well within the range reported from South A merica and South Africa under subsistence fishing and they demonstrate that, at least close to major urban centers, human recreational activ ities can have substantial effects in developed countries.