Mj. Keough et al., CORRELATIONS BETWEEN HUMAN COLLECTING AND INTERTIDAL MOLLUSK POPULATIONS ON ROCKY SHORES, Conservation biology, 7(2), 1993, pp. 378-390
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.