Anthropogenic pressures have increased the emergence and spread of infectious diseases in wildlife in recent decades, with cascading impacts on ecosystem dynamics and elevated risk to public health. Understanding factors that contribute to disease severity, and population- and community-level impacts, is critical to predicting and mitigating infectious disease outbreaks. We aimed to investigate how host genetic factors contribute to harbor seal susceptibility to phocine distemper virus (PDV), a virus that has caused variable levels of mortality among pinniped populations across the North Atlantic. We conducted whole-genome sequencing of harbor seals that were stranded during and after a PDV outbreak that occurred in the Northeastern United States in 2018 and used genome-wide association and FST-based approaches to identify genetic variants putatively associated with survival. A subset of harbor seals (10 cases, 10 controls) were sequenced at high coverage (~58×) to generate a reference haplotype panel and impute genotypes in the remaining samples (37 cases, 45 controls), which were sequenced at a lower coverage (~4×). On investigation of 148,644 filtered single nucleotide polymorphisms, we identified 33 candidate genes related to innate and adaptive immunity and 37 genes related to the nervous system that were associated with harbor seal survival. These results provide further evidence for the importance of immunogenetic variation and highlight additional key pathways and biological processes that may confer resistance to PDV. Genome-wide approaches, which can reveal the complexity of genetic variation underpinning disease-associated traits, are critical tools to help us understand and potentially predict the impact of future disease outbreaks.
Natural infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been documented in over 60 animal species, some distantly related. Several marine mammals have been predicted as highly susceptible to SARS-CoV-2 infection based on the homology of their ACE2 receptors to those of humans. To assess potential exposure of marine mammals to SARS-CoV-2, we conducted an opportunistic survey from 2020 to 2025 and tested 1,808 swabs and 378 serum samples from 21 marine mammal species in the United States. All the swabs tested by RT-qPCR were negative, indicating the absence of active infection. A low level of SARS-CoV-2 neutralizing antibodies was detected in three pinniped species, including Phoca vitulina (harbor seal, 13.6%, 95% CI: 5.2-27.4%), Zalophus californianus (California sea lion, 7%, 95% CI: 1.9-17.0%), and Halichoerus grypus (grey seal, 3.7%, 95% CI: 0.5-12.7%). These findings represent the first serological evidence of SARS-CoV-2 exposure in marine mammals in the United States, highlighting the need for continued monitoring of these populations and further research on SARS-CoV-2 transmission dynamics in wildlife.
Conserving marine predators is tantamount to maintaining functional marine ecosystems. Though intensively studied in other regions, little is known about at-sea movements and diving behaviors of a recovering population of grey seals (Halichoerus grypus atlantica) inhabiting northeastern United States continental shelf waters. Young-of-year grey seals may be particularly vulnerable to threats due to a lack of parental care postweaning. There is a need to establish baseline knowledge of at-sea behaviors in the face of large-scale ocean industrialization. We deployed 63 satellite relay data loggers on young-of-year grey seals to investigate postweaning at-sea movements and dive behaviors prior to the installation of offshore wind turbines. Young-of-year grey seals dispersed widely across the continental shelf waters. Collective utilization distributions of seals overlapped with offshore wind planning areas in the winter and spring months, and overlap was lowest in the summer when the seals dispersed northeastward. Maximum diving depth and duration increased in the first two months of nutritional independence and stabilized by April. Dives were classified as being either benthic or pelagic depending on dive depth relative to bathymetry. Seals conducted more benthic diving in the spring and this coincided spatiotemporally with habitat and phenology of an important prey species. Following a diel trend, benthic diving peaked during daylight hours, while pelagic diving occurred more frequently at night. Benthic dives occurred more frequently than pelagic dives in sandy shoals and banks. Furthermore, seals conducted more benthic than pelagic dives in wind energy planning areas. Ours is the first comprehensive study on the horizontal movement and diving behaviors in the U.S. population of grey seals, contributing knowledge on the at-sea habits of a vulnerable demographic in relation to other anthropogenic uses of the marine environment. This information will serve as valuable input to conservation management and mitigation plans, and it contributes necessary regional context to the broader understanding of grey seal ontogeny across the North Atlantic. Furthermore, these results provide important baseline information for future comparative analyses of grey seal behavior as offshore wind development expands in scope in this region.
We report the spillover of highly pathogenic avian influenza A(H5N1) into marine mammals in the northeastern United States, coincident with H5N1 in sympatric wild birds. Our data indicate monitoring both wild coastal birds and marine mammals will be critical to determine pandemic potential of influenza A viruses.
Over the past several decades, the Gulf of Maine has experienced significant socio-ecological change. Coastlines have become more densely populated and developed, rapid and dramatic climate change has affected coastal ocean environments, and seal populations have grown as a result of federal protections. Long-term data sets from marine mammal stranding networks represent a valuable resource for investigating indicator species for coastal ocean health during this period of change. Using data collected from stranded harbor (Phoca vitulina), harp (Pagophilus groenlandicus), and gray (Halichoerus grypus) seals from 2002 to 2017 in Massachusetts, New Hampshire, and Maine, we tested for spatiotemporal correlations between stranding density and human population density, size of and proximity to seal haul-outs, sea surface temperature, North Atlantic Oscillation, snowfall, and sea ice extent. We found that in the Gulf of Maine proximity to coastal human population centers and large seal haul-outs are the greatest drivers of reported seal stranding density. Environmental factors played an important role only for harp seals, which do not breed in the study area, although recent shifts in the environmental seascape have the potential to affect all seal species in the Gulf of Maine.
