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Highly migratory species pose unique conservation and management challenges, especially when significant mortality occurs away from breeding concentrations. Population genetics and genomics may help with the appropriate management of these species by (1) determining the population genetic structure of a species across its range, and (2) allowing the assignment of individuals to their breeding source. The northern fulmar (Fulmarus glacialis; Procellariiformes: Procellariidae) is a seabird species that breeds in colonies throughout the North Atlantic and Pacific oceans. This species ranges widely across ocean basins during the non-breeding season and is exposed to a variety of threats throughout the annual cycle. The impact of mortality during the nonbreeding season on individual breeding colonies is unknown but has important ramifications for conservation and management. In this study we used restriction site-associated DNA sequencing (RADseq) to provide 6614 genome-wide single nucleotide polymorphisms (SNPs) to investigate population genetic structure of northern fulmars using 127 individuals from six breeding colonies spanning the Atlantic. Additionally, birds of unknown breeding origin were sampled from two locations: (1) offshore in the Labrador Sea, and (2) the Baffin Bay-Davis Strait region (NAFO subarea 0), as bycatch in gillnets set for Greenland halibut (Reinhardtius hippoglossoides). We found weak genetic differentiation among breeding colonies, which we suggest reflects historical associations as well as contemporary gene flow among populations. Most bycatch birds were likely from nearby breeding colonies in the eastern Canadian Arctic, but the exact breeding origins were difficult to determine due to the lack of differentiation between colonies.

Hybridization can negatively impact one or both taxa involved and therefore pose conservation concerns. Climate change is expected to increase the rate of hybridization particularly in polar regions, and so investigating hybridization in Arctic and Antarctic species is important for conservation. Hybridization and genetic introgression have been observed between Pacific populations of thick-billed (Uria lomvia) and common murres (Uria aalge), species of seabirds with arctic and low arctic/temperate distributions, respectively. We employed double-digest restriction site-associated DNA sequencing (ddRADseq) to generate thousands of genome-wide markers to investigate hybridization and introgression in 133 thick-billed and 119 common murres sampled from 15 colonies throughout the North Atlantic. We used molecular assignments and principal components analysis to identify hybrids and quantify genetic introgression. Despite previous reports of hybridization between murre species in the Atlantic, we found no evidence for hybrid individuals in our dataset, and limited evidence for introgression. Our results suggest that hybridization between Atlantic murre species is rare, and does not currently pose a conservation concern for either species. Our study provides baseline data for monitoring hybridization between murres in the Atlantic to assess future impacts of climate change on these species.