The D values listed in Table 1 suggest no overall tendency for heterozygote deficiencies to occur in any of the samples, suggesting that none represents a heterogeneous mixture of genet- ically discrete subpopulations. For both allozyme and RFLP loci, heterozygosity levels were lowest in the North American samples. At the RFLP loci, mean heterozygosity was highest in the Norwegian coastal sample (Balsfj- ord) despite this population being monomorphic for 2 of the 17 polymorphisms scored. No correlation was seen between allozyme and RFLP heterozygosities among populations from similar geographic regions (r = 0.63, P = 0.176).