Changes in shellfish species composition and mean shell size from a Late-Holocene record of the west coast of Southern Africa

This paper presents and discusses the results of a systematic analysis of the shellfish assemblage recovered from Pancho's Kitchen Midden, a site located in the western Cape coast of South Africa. Several-hypotheses are considered in an attempt to explain the observed changes in shellfish frequencies and shell size. Changes in species composition in this particular sequence are mostly attributable to changes in collecting practices. Shellfish gathering was generally undertaken within the mid and low-intertidal zones throughout the Late Holocene, with slightly more frequent collections within the upper subtidal in the last 600 years. Changes in water turbidity, on the other band, seem to explain most of the variability in the mean sizes of black mussels. Nevertheless, intense collection of large numbers of black mussels seems to have been an additional factor in bringing mussel sizes to a minimum around 3000 sp. Subsequent recovery of mean mussel sizes appears to be the result of several factors: improvement in marine productivity and low water turbidity, greater access to large individuals inhabiting the low intertidal and upper subtidal, and/or relatively low levels of shellfish exploitation by people. Changes in sea surface temperature of the magnitude reported here do not appear related to changes in species composition and shell size. The comparison of this shellfish sequence with others from nearby sites, and analysed in a similar fashion, would be essential for the reconstruction of pre-Colonial shellfish-gathering practices at the western Cape. (C) 1997 Academic Press Limited.