LB 20-211 - Estimating the effective population size and historical demography of leopard seals (Hydrurga leptonyx) in the Antarctic Peninsula.

Background/Question/Methods:

The leopard seal (Hydrurga leptonyx) is an apex marine predator in the Antarctic ecosystem with a determinant role in ecosystem functioning through predator-prey interactions. Recently, summer leopard seal sightings have steadily increased in the Northern Antarctic Peninsula (NAP). There, leopard seals have been predating Antarctic fur seal (Arctocephalus gazella) pups at high rates, partially contributing to this species population collapse in the NAP. Leopard seal abundance is difficult to estimate directly because observational surveys are costly and hold a high degree of uncertainty. Therefore, population trends are largely unknown. In this study, we used molecular genetic methods to estimate the effective population size (N_E) and historical demography of leopard seals. We sequenced a 405-base pair (bp) fragment of the mitochondrial DNA (mtDNA) control region of 90 seals sampled at the NAP by the US Antarctic Marine Living Resources Program (US AMLR) during the austral summers of 2008 – 2019.

Results/Conclusions:

Our genetic diversity assessment revealed moderate to high nucleotide and haplotype diversity relative to other Antarctic ice seals (π= 0.013; Hd= 0.96). We estimated a theta value (Θ = 0.039), which resulted in a large NE > 500,000 individuals. Our analyses also rejected the null hypothesis of constant population size (Fu Fs = –14.76) with a demographic expansion around 35,000 years before present (YBP; τ = 3.64). This timing of expansion contrasts the pattern of Pleistocene population increase estimated to have occurred earlier in the Pleistocene for other Antarctic ice seals. Our study provides valuable baseline population estimates for a poorly known apex predator in one of the most rapidly warming regions of the planet.