Sustainable yields: gamebirds as a harvestable resource.

Abstract

Sustained harvesting relies upon a population's natural tendency to increase after being reduced below its equilibrium level. The strength of this tendency and the equilibrium level itself depend on the quality of the species' environment, which encompasses habitat, food, predators, disease and population density. It is possible to improve this quality by appropriate management based on a knowledge of the species' biology.

Harvesting automatically induces a reduction in stock size compared to the unharvested situation. Under continued harvesting, the population stabilises at a new level below the original equilibrium level - this produces a sustainable yield.

Two common features of gamebird biology are the potential for rapid increase, due to a large clutch size and early maturity, and density-dependent processes governing gains in summer and losses in winter. These provide for partial compensation to harvesting losses, and enable the harvested population to stabilise quickly when the environment is right.
Several species of gambirds are declining, and there is pressure to ban shooting. A proven model of a Grey Partridge (Perdix perdix) population simulates the outcome of different policies. Currently, the partridge's arable environment is deteriorating through modern agricultural practices. A stop to shooting is unable to halt its decline in the long term as the root cause of the decline remains. Environmental improvement, however, even with shooting, rapidly leads to an increase in stocks above the level obtained in the unshot unmanaged situation. Wise use lies in using harvesting to provide the incentive and revenue for environmental management.