Identification of stocks of the exploited limpets Patella aspera and P-candei at Madeira Archipelago by allozyme electrophoresis

Allozyme electrophoresis was used to investigate stock integrity of Patella aspera (= P. ulyssiponensis) and Patella candei (Mollusca, Patellogastropo da) from the Madeira Archipelago. Samples from the north of the island of M adeira (Porto Moniz) and the north of Deserts Grande were taken for both sp ecies, and a sample of P. aspera was also taken from the south of the islan d of Madeira (Canico). Twenty-one putative loci were resolved and analyzed for both species. Significant differences in allele frequencies were found between locations in each species. suggesting the presence of different gen etic stocks. P. candei was found to be slightly structured with a small sta ndardized variance in allele frequencies between samples from Porto Moniz a nd Deserta Grande (F-ST = 0.036); whereas, P. aspera was highly structured, with an F-ST value over all subpopulations of 0.157. Our results indicate more genetic interchange between the populations from the north of Madeira and Deserta Grande than between north and south Madeira. Our findings are c onsistent with surface water-mass circulation patterns from northwest to so utheast along the Madeira Archipelago, determined mainly by the Canary Curr ent. Species with low dispersal and a high degree of spatial genetic struct uring among subpopulations are more susceptible to collapse caused by over fishing than those with high dispersal capabilities; therefore, the individ ual management and control of these biological units is recommended.