Intertidal population structure of the edible mollusc Turbo sarmaticus (Vetigastropoda) at an unexploited and exploited sites along the coast of the Eastern Cape Province, South Africa

Abstract

The intertidal population structure of the large edible gastropod Turbo sarmaticus was examined at four sites along the Eastern Cape Province of South Africa. One site was free from exploitation, two were subjected to low levels of exploitation and one was heavily exploited. Within the intertidal zone at all sites there was a  size-related distribution, with smaller animals being found towards the upper mid-shore and larger animals occurring in a downshore direction. The mean shore densities (1.2–animals/m2) and biomass (4.4–9.4 g/m2) of T. sarmaticus at the sites where there was no, or minimal, exploitation of animals were not significantly different (P < 0.001). However, the largest animals (up to 110mmshell length) were found at the unexploited site, an offshore island. The lowest density (0.2 animals/m2) and biomass (0.4 g/m2) of T. sarmaticus was recorded at the site where the exploitation of this gastropod was intense. In addition, no animals of a legally exploitable size (>70 mm shell length) were found. It is suggested that intense over-exploitation is threatening the population at this site.

Key words: density, biomass, size frequency, intertidal distribution.