Effects of harvesting and density dependence on the demography of sandy beach populations: The yellow clam Mesodesma mactroides of Uruguay

Abstract

Sandy beach ecologists concur that natural populations living in these harsh environments are controlled almost exclusively by physical factors, biotic factors being largely irrelevant. This paper provides evidence that human-induced perturbations as well as biotic, density-dependent processes also influence sandy beach populations. Results were obtained from a long-term study (8 yr) of the artisanally harvested yellow clam Mesodesma mactroides on a Uruguayan exposed sandy beach. The study included an experimental manipulation of fishing effort based on the closure of the clam fishery for 32 consecutive months. Fine-scale demographic parameters, such as age-specific survival probability and fertility, as well as coarse-scale demographic parameters, such as age composition, elasticity to demographic parameters, adult clam density, and population growth rate, were significantly affected by fishing effort and/or adult density. These results yield useful information from the management and conservation points of view, such as the threshold range of parent stock densities and fishing mortality levels capable of supporting a sustainable yield over time. Critical demographic parameters for population growth rate are also highlighted.