Microsatellite analysis of genetic diversity in the squid Illex argentinusduring a period of intensive fishing

Levels of genetic diversity and population differentiation were examined in temporally (1990 to 1997) and geographically separated samples of the arge ntine short-finned squid Illex argentinus using 7 microsatellite loci. Numb er of alleles (mean number of alleles per locus over all samples = 24.1) an d heterozygosity (mean observed heterozygosity per sample = 0.84) were high for all samples, indicating that these loci have a greater potential utili ty for investigating population genetic structure than allozyme markers use d in previous studies. Genetic diversity did not differ significantly betwe en samples taken 5 yr after commencement of the fishery (1990) and those co llected during a period of progressively intense fishing pressure (1994 and 1997). Several small but significant differences in between-sample genetic variation (F-ST) were observed, but these could not confirm the previous s uggestion of cryptic species or several well-defined stocks within the fish ed population.