Abstract

RAMIREZ, Rubén; TUYA, Fernando  and  HAROUN, Ricardo J. Potential effects of man harvesting on gastropod molluscs of commercial interest (Osilinus spp. and Patella spp.) in the Canarian Archipelago. Rev. biol. mar. oceanogr. [online]. 2009, vol.44, n.3, pp. 703-714. ISSN 0718-1957.  doi: 10.4067/S0718-19572009000300016.

This study assessed the effects of human influences over the abundance and size patterns of five species of gastropods (top-shell snails and limpets) commonly collected in the Canarian Archipelago: `burgado hembra' (Osilinus atrata), `burgado macho' (Osilinus sauciatus), `lapa blanca' (Patella aspera), `lapa negra' (Patella candei crenata) and `lapa de sol' (Patella rustica). We studied patterns of abundance and size of these species across three islands (Lanzarote, La Graciosa and Alegranza) corresponding to three levels of human influence: high, medium and low, respectively; which were quantified through three indicators: human pressure (inhabitants km^-1 d^-1), accessibility to the coast (km of sealed and unsealed roads), and volumes of capture (kg). The abundances of O. atrata and P. aspera were statistically higher at Alegranza than at La Graciosa and Lanzarote, whereas the density was 10 to 15 times larger at Alegranza for four of the five studied species. Significant differences in the size structure of the species among islands (= levels of human influence) were also observed. Not only all large-sized individuals disappeared at Lanzarote and La Graciosa, yet there was a decrease in numbers for the majority of size ranges. Thought populations of top-shell snails and limpets were affected by natural variability, human activities turned out to be the major driver for the observed differences among islands. These results seriously question the effectiveness of the current shellfish regulations contained in the Regional Fish Law.

Keywords : intertidal; marine resources; overexploitation; Canary Islands.