Rates of increase in gray seal (Halichoerus grypus atlantica) pupping at recolonized sites in the United States, 1988-2019

Sequence diversity and differences at the highly duplicated MHC-I gene reflect viral susceptibility in sympatric pinniped species

Differences in disease susceptibility among species can result from rapid host-pathogen coevolution and differences in host species ecology that affect the strength and direction of natural selection. Among two sympatric pinniped species that differ in sociality and putative disease exposure, we investigate observed differences in susceptibility through an analysis of a highly variable, duplicated gene family involved in the vertebrate immune response. Using high-throughput amplicon sequencing, we characterize diversity at the two exons that encode the peptide binding region of the major histocompatibility complex class I (MHC-I) gene in harbor (N = 60) and gray (N = 90) seal populations from the Northwest Atlantic. Across species, we identified 106 full-length exon 2 and 103 exon 3 sequence variants and a minimum of 11 duplicated MHC-I loci. The sequence variants clustered in 15 supertypes defined by the physiochemical properties of the peptide binding region, including a putatively novel Northwest Atlantic MHC-I diversity sublineage. Trans-species polymorphisms, dN/dS ratios, and evidence of gene conversion among supertypes are consistent with balancing selection acting on this gene. High functional redundancy suggests particularly strong selection among gray seals at the novel Northwest Atlantic MHC-I diversity sublineage. At exon 2, harbor seals had a significantly greater number of variants per individual than gray seals, but fewer supertypes. Supertype richness and private supertypes are hypothesized to contribute to observed differences in disease resistance between species, as consistently, across the North Atlantic and many disease outbreaks, gray seals appear to be more resistant to respiratory viruses than harbor seals.

A Community Science Approach to Conservation Challenges Posed by Rebounding Marine Mammal Populations: Seal-Fishery Interactions in New England

Between 1880–1962, gray and harbor seals were targeted in legal seal bounty hunts across Maine and Massachusetts due to a perceived competition with commercial fisheries. Following their extirpation 50 years ago, legislative protections allowed seals to recolonize historical grounds along the New England coast. With this conservation success story, conflict has re-emerged as seen in the numerous media articles reflecting a temperament beckoning to the past century, with calls to cull the population and the spread of misinformation. The return of seals after decades of near-absence has created a new ecological and psychological baseline for New Englanders where for three generations, seals were rarely present. Although seals are statutorily protected species, unlike the tools and resources available for depleted, threatened or endangered species, the support needed to increase opportunities for coexistence of humans with rebounding pinnipeds, are comparatively lacking. Even as gray seals have the highest fisheries bycatch levels of any marine mammal in the U.S., resources to address these management challenges are minimal due to limitations and prioritization processes for committing available support. While seal conservation has been a success, the manner in which management is often separately applied to ecosystem elements (e.g., harvested species, protected species) contributes to knowledge gaps, and a disconnect between the goals of conservation to sustainably utilize natural resources while also protecting the intrinsic value of resources for ecosystem health. Solutions to such coexistence challenges could benefit from a more holistic ecosystem conservation approach. To address these disconnects, a two-day workshop was convened to understand seal-fishery interactions where we provided opportunities for community members to meet and learn from one another including, but not limited to, fishermen, natural resource managers, marine mammal stranding response personnel and scientists. A convening that might otherwise result in tumultuous and adversarial engagement, we used as a tool to engage. This community science approach led to long-term relationships that have allowed for successful applied, and community driven, solutions. Here we share the lessons learned and subsequent partnerships. Our intent is to share our approach to address other marine mammal conservation conflict challenges, allowing for collaborative pathways toward long-term coexistence.

Fine-scale vertical habitat use of white sharks at an emerging aggregation site and implications for public safety

Abstract ContextOver the past decade, the coastal waters off Cape Cod, Massachusetts, have emerged as the only known aggregation site for the white shark (Carcharodon carcharias) in the western North Atlantic. During periods of seasonal residency, white sharks patrol the shoreline in search of pinniped prey, bringing them in close proximity to popular beaches where people recreate. AimTo examine whether white sharks off Cape Cod are more likely to occupy shallow depths (and consequently more likely to overlap with recreational water users) under certain conditions. MethodsWe deployed short-term, pop-up satellite archival transmitting (PSAT) tags and acoustic transmitters on 14 subadult and adult white sharks off the coast of Cape Cod during the summer and fall of 2017. PSAT tags provided fine-scale depth and temperature data, which were combined with high-resolution location data obtained from an acoustic telemetry array, to identify the depth and temperature preferences of white sharks when resident in the area. Key resultsSharks spent the majority (95%) of tracked time at depths of 0–31m and at temperatures from 8.9°C to 20.7°C. During resident periods along Cape Cod, individuals spent almost half (47%) of their time at depths of less than 4.5m, but made frequent excursions to mid-shelf depths, alternating between the surf zone and deeper offshore waters. Sharks were slightly more likely to occupy shallow depths at night during the new moon. The relationship between shark depth and lunar phase varied over the course of the day, suggesting the mechanism underlying lunar effects differs among diel periods. ConclusionsAlthough the overall risk posed to humans by white sharks is low, there is a high potential for overlap between white sharks and recreational water users off Cape Cod. The risk of interaction may be slightly higher during periods when local environmental conditions favour the species’ predatory stealth by influencing prey behaviour or detectability. ImplicationsThis study provides the first glimpse into the fine-scale vertical habitat use of white sharks off Cape Cod, which can be used to better understand the risk to recreational water users and to inform public safety practices.