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Biologging tools can provide invaluable information on the movement and behaviour of animals, facilitating the elucidation of ecological dynamics, especially for wide-ranging species, and supporting conservation and management efforts. Harbour seals (Phoca vitulina) exhibit extensive habitat plasticity in their vast range across the northern hemisphere, with likely recent increases in abundance at northern latitudes, yet details of their movement behaviour in subarctic areas remain largely unknown. We used satellite-telemetry data, including nearly 5,000 locations and over 12,000 dives, obtained from six harbour seals tagged in western Hudson Bay from 2021 to 2023, to address the knowledge gap on their movement behaviour between marine and freshwater habitats in subarctic regions. We document the behavioural patterns, transit speeds, and diverse aquatic system usage, including detailed records of a harbour seal track traversing over 170 km upriver on three separate trips along the Seal River, Canada. Notably, we observed a rapid downstream transit from the Seal River to Hudson Bay, covering 214 km within a single day. Additionally, we highlight the prevalence of short dive durations in the Seal and Churchill Rivers, in contrast to longer dive durations in Hudson Bay. These insights complement existing evidence of harbour seal occurrences and river use at northern latitudes, as well as enhance our understanding of harbour seal movement ecology within Hudson Bay which can be used to better inform conservation and management strategies between connected freshwater and marine environments in the Arctic. [ABSTRACT FROM AUTHOR]

Biologging tools can provide invaluable information on the movement and behaviour of animals, facilitating the elucidation of ecological dynamics, especially for wide-ranging species, and supporting conservation and management efforts. Harbour seals (Phoca vitulina) exhibit extensive habitat plasticity in their vast range across the northern hemisphere, with likely recent increases in abundance at northern latitudes, yet details of their movement behaviour in subarctic areas remain largely unknown. We used satellite-telemetry data, including nearly 5,000 locations and over 12,000 dives, obtained from six harbour seals tagged in western Hudson Bay from 2021 to 2023, to address the knowledge gap on their movement behaviour between marine and freshwater habitats in subarctic regions. We document the behavioural patterns, transit speeds, and diverse aquatic system usage, including detailed records of a harbour seal track traversing over 170 km upriver on three separate trips along the Seal River, Canada. Notably, we observed a rapid downstream transit from the Seal River to Hudson Bay, covering 214 km within a single day. Additionally, we highlight the prevalence of short dive durations in the Seal and Churchill Rivers, in contrast to longer dive durations in Hudson Bay. These insights complement existing evidence of harbour seal occurrences and river use at northern latitudes, as well as enhance our understanding of harbour seal movement ecology within Hudson Bay which can be used to better inform conservation and management strategies between connected freshwater and marine environments in the Arctic.

The assumed definitive host of the heartworm Acanthocheilonema spirocauda (Onchocerdidae; Filarioidea) is the harbour seal (Phoca vitulina). This filaroid nematode parasitizing in cardiac ventricles and blood vessel lumina of harbour seals (P. vitulina) has a low prevalence and seldom causes severe health impacts. The seal louse (Echinophthirius horridus) is the assumed intermediate host for transmission of A. spirocauda filariae between seals, comprising a unique parasite assembly conveyed from the terrestrial ancestors of pinnipeds. Although grey seals (Halichoerus grypus) are infected by seal lice, heartworm infection was not verified. Analysing a longterm dataset compiled over decades (1996–2021) of health monitoring seals along the German coasts comprising post mortem investigations and archived parasites, 2 cases of A. spirocauda infected male grey seals were detected. Tentative morphological identification was confirmed with molecular tools by sequencing a section of mtDNA COI and comparing nucleotide data with available heartworm sequence. This is the first record of heartworm individuals collected from the heart of grey seals at necropsy. It remains puzzling why heartworm infection occur much less frequently in grey than in harbour seals, although both species use the same habitat, share mixed haul-outs and consume similar prey species. If transmission occurs directly via seal louse vectors on haul-outs, increasing seal populations in the North- and Baltic Sea could have density dependent effects on prevalence of heartworm and seal louse infections. It remains to be shown how species-specificity of filarial nematodes as well as immune system traits of grey seals influence infection patterns of A. spirocauda.

Peptidylarginine deiminases (PADs) are phylogenetically conserved calcium-dependent enzymes which post-translationally convert arginine into citrulline in target proteins in an irreversible manner, leading to functional and structural changes in target proteins. Protein deimination can cause the generation of neo-epitopes, affect gene regulation and also allow for protein moonlighting and therefore facilitate multifaceted functions of the same protein. PADs are furthermore a key regulator of cellular release of extracellular vesicle (EVs), which are found in most body fluids and participate in cellular communication via transfer of cargo proteins and genetic material. In this study, post-translationally deiminated proteins and EVs were assessed in sera of two seal species, grey seal and harbour seal. We report a poly-dispersed population of serum-EVs, which were positive for phylogenetically conserved EV-specific markers and characterised by transmission electron microscopy. A number of deiminated proteins critical for immune and metabolic functions were identified in the seal sera and varied somewhat between the two species under study, while some targets were in common. EV profiles of the seal sera further revealed that key microRNAs for inflammation, immunity and hypoxia also vary between the two species. Protein deimination and EVs profiles may be useful biomarkers for assessing health status of sea mammals, which face environmental challenges, including opportunistic infection, pollution and shifting habitat due to global warming. Image 1 • Key immune and metabolic proteins were identified as deiminated in seal sera. • EV serum profiles varied somewhat between seal species. • EV microRNA cargo varied between seal species for inflammatory related miR155, miR21 and hypoxia related miR210. • EV profiles and deiminated proteins are novel biomarkers in seal sera. [ABSTRACT FROM AUTHOR]

In several studies, heterozygosity measured at around 10 microsatellite markers correlates with parasite load. Usually the effect size is small, but while this may reflect reality, it may also be possible that too few markers are used or the measure of fitness contains too much error to reveal what is actually a much stronger underlying effect. Here, we analysed over 200 stranded harbour seals (Phoca vitulina) for an association between lungworm burden and heterozygosity, conducting thorough necropsies on the seals and genotyping the samples obtained for 27 microsatellites. We found that homozygosity predicts higher worm burdens, but only in young animals, where the worms have the greatest impact on fitness. Testing each locus separately, we found that a significant majority reveal a weak but similar trend for heterozygosity to be protective against high lungworm burden, suggesting a genome-wide effect, that is, inbreeding. This conclusion is supported by the fact that heterozygosity is correlated among markers in young animals but not in otherwise equivalent older ones. Taken as a whole, our results support the notion that homozygosity increases susceptibility to parasitic infection and suggest that parasites can be effective in removing inbred individuals from the population.Heredity (2008) 100, 587–593; doi:10.1038/hdy.2008.18; published online 9 April 2008 [ABSTRACT FROM AUTHOR]

Abstract: Lactating marine mammals provision their offspring either by providing large amounts of lipid-rich milk over a short period during which females fast (capital provisioning), or smaller amounts of less energetically dense milk over an extended period during which females forage (income provisioning). While it has long been recognized that these two strategies carry different costs for the female, the effect of these two strategies on the physiological status of newly weaned pups has rarely been considered. Recent comparative studies on the development of diving capacity, as assessed by measuring total body oxygen stores, have demonstrated that the provisioning strategy does affect pup development. Phocid pups, which grow rapidly during their brief nursing period undergo a strong post-parturition anemia and are weaned with relatively immature oxygen stores, possibly due to limited iron intake. Otariid pups, which grow at a slower pace over a longer period, are weaned with body oxygen stores that are significantly more mature. This suggests that newly independent phocid pups must quickly develop foraging skills in order to acquire the nutrients necessary to mature physiologically. In contrast, newly weaned otariids have more mature oxygen stores, and may have previous foraging experience, which may allow for increased behavioral flexibility. [Copyright &y& Elsevier]

Tidal patterns in feeding behaviour are known in several upper trophic level predators. Although harbour seal (Phoca vitulina richardsi) movements between resting and foraging areas are often correlated with tidal phase, little is known about tidal influences on seal foraging because it is difficult to make direct observations of predation events. This study sought to determine whether harbour seals exhibit tidal patterns in their at-sea distribution, abundance, and foraging success and to discuss how changes in capture rates or prey types might affect the ability of an individual to meet its daily energy requirement. During 1995–97, seal abundance in the water during flooding tides was significantly greater than median daily abundance. Seals aggregated near a channel constriction. Salmon accounted for 50% and 87% of observed captures of single, large fish in 1996 and 1997, respectively. Predation on schooling fishes involved juvenile sandlance or herring. Large-fish captures were episodic (16.9% and 27.5% of observations with nonzero capture rates) and occurred more often on the incoming tide near constricted water flow. Median per capita capture rates were highest in currents during slower flooding (0.31 fish·seal–1 h–1). Surface attacks on forage fish schools were more common than large-fish captures (54.0% and 66.7% of observations with at least one attack on forage fish). Night-time and subsurface feeding were not assessed. Given what is known about seal food requirements, tidal differences in capture rates are predicted to have a significant impact on both the hunting strategy and energy intake of individuals. Results support the idea that interactions among tidal currents, topographic features, and fish play a role in structuring marine predator–prey dynamics. [ABSTRACT FROM AUTHOR]