Conservation genetics of the Hawaiian monk seal

The endangered and endemic Hawaiian monk seal (Monachus schauinslandi ) was hunted to near-extinction in the late 19th century. Though the species made a partial recovery by 1960, its current decline raises questions regarding genetic diversity, inbreeding, population structure, effective population size and reproductive potential. To assess the impact of genetics on recovery of the Hawaiian monk seal, I isolated species-specific microsatellite loci and analyzed more than 2400 specimens collected over three decades. The species exhibits extremely low genetic diversity, with unprecedented levels of allelic diversity and heterozygosity (A = 1.1, He = 0.026). There is little indication of contemporary inbreeding (FIS = 0.018), perhaps due to high effective migration rates (Nem = 1--33) among subpopulations. Analyzing ∼85% of the extant population and 14 pup cohorts, I find weak population structure (theta < 0.01) throughout the Hawaiian archipelago, indicating a single management unit. The effective population size of the species (Ne = 332) is slightly lower than half the number of adults (N = 743) and slightly lower than twice the number of pups born in a cohort (N = 165--245). At low effective population sizes (Ne < 500), future population viability is threatened by inadequate genetic variability. Considering the Hawaiian monk seal's extremely low genetic diversity, additional reduction should be minimized. That many adults contribute alleles to the next generation is promising, especially since on average Ne is a tenth of adult population size in wild populations. Management is working to halt the current population decline of ∼4% per year by minimizing juvenile mortality. Another possible avenue of population growth is increasing the reproductive rate. While dizygotic twinning is rare (7 cases in ∼4875 births over 27 years) in the Hawaiian monk seal, it offers a small possibility for increasing the annual reproductive output of some females. The low genetic diversity of the Hawaiian monk seal raises concern regarding its future, but there is strong potential for recovery given the low levels of inbreeding, weak population subdivision, high Ne/N ratio, and increasing incidence of twinning.