Effect of Exploitation on the Limpet Lottia gigantea: A Field Study in Baja California (Mexico) and California (U.S.A.)

Abstract

Specimens of Lottia gigantea (Sowerby) from intertidal populations, artisanal catches, and shell middens were obtained from 1985 to 1988 at 11 sites along the Pacific coasts of Baja California (Mexico) and California (U.S.A.). A scaled rating system of 0-4 was used to describe the amount of intertidal exploitation associated with visiting patterns of gatherers, accessibility, and site topography. Maximum and mean size of intertidal populations and artisanal catches decreased along a gradient of increasing exploitation. Mean size was significantly different between catches and the corresponding intertidal population. Mean size of specimens in older middens was significantly larger than in a recent midden. Measurements at the most inaccessible site inmediately after the exceptional extratropical winter storm that swept the California coast on 17-18 January 1988 showed that the storm had removed larger specimens approximating exploitation measuring 1-2 on our scale. Intertidal gathering occurs or has occurred unless it is physically prevented by topography, distance, or some kind of restriction of access. Ecological implications of exploitation were explored utilizing the conceptual model proposed by Catterall and Poiner for assessing potential impact of traditional shell gathering on intertidal molluscs. The model suggests that size at maturity of this species and its pelagic larval stage may prevent depletion by harvesting.