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Knowledge of the feeding habits of cetaceans is critical to the development of system-wide conservation strategies in marine ecosystems, yet dietary data are often lacking. To investigate the foraging ecology of long-finned pilot whales ( Globicephala melas ), we analysed stable carbon and nitrogen isotopes in skin tissue from 50 adult and juvenile animals that mass stranded in July 2023 on the Isle of Lewis, Scotland, in the Northeast Atlantic. We interpreted our isotope data with reference to published data from six delphinid species and baseline prey data from the region. We compared isotopic niche breadth among delphinid species and estimated dietary composition for long-finned pilot whales. The average isotopic values were —17.4 ± 0.9 ‰ for δ 13 C and +11.0 ± 0.7 ‰ for δ 15 N. The core isotopic niche of long-finned pilot whales overlapped with striped dolphin only, with a core niche overlap of 8.6%, suggesting some shared habitat and low trophic level prey, or foraging in habitats with lower baseline δ 15 N values. Adult male and female long-finned pilot whales showed complete isotopic niche overlap, although females displayed a wider niche. Estimated dietary contributions suggest a primarily benthopelagic foraging strategy linked to continental shelf edge and slope food webs. Our findings demonstrate the importance of deep-water prey resources to long-finned pilot whales, providing valuable insights into the early spring-summer feeding habits of the species and build baseline ecological data for the Northeast Atlantic. These results highlight the value of stable isotope analysis to advance our understanding of cetacean trophic ecology and better inform marine mammal conservation management.

Extension of known ecological niches of Brucella has included the description of two novel species from marine mammals. Brucella pinnipedialis is associated predominantly with seals, while two major Brucella ceti clades, most commonly associated with porpoises or dolphins respectively, have been identified. To date there has been limited characterisation of Brucella isolates obtained from marine mammals outside Northern European waters, including North American waters. To address this gap, and extend knowledge of the global population structure and host associations of these Brucella species, 61 isolates from marine mammals inhabiting North American waters were subject to molecular and phenotypic characterisation enabling comparison with existing European isolates. The majority of isolates represent genotypes previously described in Europe although novel genotypes were identified in both B. ceti clades. Harp seals were found to carry B. pinnipedialis genotypes previously confined to hooded seals among a diverse repertoire of sequence types (STs) associated with this species. For the first time Brucella isolates were characterised from beluga whales and found to represent a number of distinct B. pinnipedialis genotypes. In addition the known host range of ST27 was extended with the identification of this ST from California sea lion samples. Finally the performance of the frequently used diagnostic tool Bruce-ladder, in differentiating B. ceti and B. pinnipedialis, was critically assessed based on improved knowledge of the global population structure of Brucella associated with marine mammals.

Organochlorine (OC) pesticides and the more persistent polychlorinated biphenyls (PCBs) have well-established dose-dependent toxicities to birds, fish and mammals in experimental studies, but the actual impact of OC pollutants on European marine top predators remains unknown. Here we show that several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. In a large pan-European meta-analysis of stranded (n = 929) or biopsied (n = 152) cetaceans, three out of four species:- striped dolphins (SDs), bottlenose dolphins (BNDs) and killer whales (KWs) had mean PCB levels that markedly exceeded all known marine mammal PCB toxicity thresholds. Some locations (e.g. western Mediterranean Sea, south-west Iberian Peninsula) are global PCB \"hotspots\" for marine mammals. Blubber PCB concentrations initially declined following a mid-1980s EU ban, but have since stabilised in UK harbour porpoises and SDs in the western Mediterranean Sea. Some small or declining populations of BNDs and KWs in the NE Atlantic were associated with low recruitment, consistent with PCB-induced reproductive toxicity. Despite regulations and mitigation measures to reduce PCB pollution, their biomagnification in marine food webs continues to cause severe impacts among cetacean top predators in European seas.

Parasite biodiversity in cetaceans represents a neglected component of the marine ecosystem. This study aimed to investigate the distribution and genetic diversity of anisakid nematodes of the genus Anisakis sampled in cetaceans from the Northeast Atlantic Ocean and the Mediterranean Sea. A total of 478 adults and pre-adults of Anisakis spp. was identified by a multilocus genetic approach (mtDNA cox2, EF1 α − 1 nDNA and nas 10 nDNA gene loci) from 11 cetacean species. A clear pattern of host preference was observed for Anisakis spp. at cetacean family level: A. simplex (s.s.) and A. pegreffii infected mainly delphinids; A. physeteris and A. brevispiculata were present only in physeterids, and A. ziphidarum occurred in ziphiids. The role of cetacean host populations from different waters in shaping the population genetic structure of A. simplex (s.s.), A. pegreffii and A. physeteris was investigated for the first time. Significant genetic sub-structuring was found in A. simplex (s.s.) populations of the Norwegian Sea and the North Sea compared to those of the Iberian Atlantic, as well as in A. pegreffii populations of the Adriatic and the Tyrrhenian Seas compared to those of the Iberian Atlantic waters. Substantial genetic homogeneity was detected in the Mediterranean Sea population of A. physeteris. This study highlights a strong preference by some Anisakis spp. for certain cetacean species or families. Information about anisakid biodiversity in their cetacean definitive hosts, which are apex predators of marine ecosystems, acquires particular importance for conservation measures in the context of global climate change phenomena.

Growing anthropogenic pressures increasingly impact marine wildlife, with cetaceans being particularly vulnerable to cumulative effects of stressors due to their position as top predators. As sensors and sentinels of ocean health, cetaceans offer critical insight into known and emerging threats to marine ecosystems. Stranding schemes provide a cost-effective means to assess mortality rates and population demographics, offering insights that are often challenging to obtain through live monitoring. Using a 30-year dataset from the Scottish Marine Animal Stranding Scheme (SMASS) we demonstrate how opportunistically obtained stranding data can be used to monitor populations and guide conservation strategies. Species were clustered into broad ecological groups - baleen whales, short-beaked common dolphins, deep divers, harbour porpoises and pelagic dolphins - for spatiotemporal analysis of stranding patterns. All groups showed increases in annual stranding rates over the study period, with common dolphins and baleen whales exhibiting exponential increases, suggesting these species may be facing heightened pressures. Distinct seasonal and spatial trends were detected, with harbour porpoises predominantly stranding on the east coast and other groups clustering to Scotland’s west coast. Identifying these trends helps focus surveillance and mitigation efforts, underscoring the importance of this approach for monitoring vulnerable species.

Anisakid nematodes are a globally distributed group of marine mammal parasites. Kogiid whales, including the pygmy sperm whale Kogia breviceps, host an assemblage of specific anisakid species. Currently, three species are known to be specific to kogiid hosts, i.e., Skrjabinisakis paggiae, S. brevispiculata, and the less studied Pseudoterranova ceticola. The aim of this study was to investigate the species diversity of anisakid nematodes sampled from a pygmy sperm whale stranded in 2013 at the edge of its distribution range in the Northeast Atlantic, specifically in the North of Scotland. Nematodes were assigned to genus level based on morphology and identified by sequence analysis of the mtDNA cox2 gene and the rDNA ITS region. The present finding represents the first observation of syntopic occurrence of adult stages of S. brevispiculata, S. paggiae, and P. ceticola in a pygmy sperm whale in the Northeast Atlantic, and represent the northernmost record of these species in this area. Skrjabinisakis brevispiculata was the most abundant species, accounting for 55% of the identified nematodes, predominantly in the adult stage. Anisakis simplex (s.s.) was also abundant, with most specimens in the preadult stage, followed by S. paggiae and P. ceticola. The pygmy sperm whale is rarely documented in Scottish waters, and its occurrence in the area could suggest expansion of its geographic range. The presence of S. brevispiculata, S. paggiae, and P. ceticola in this whale species in this region may indicate a shift in the whole host community involved in the life cycle of these parasites in northern waters. However, it is also plausible that these parasites were acquired while the whale was feeding in more southern regions, before migrating northbound.

Monitoring the nutritional health of cetaceans has become increasingly important in a changing environment, where multiple stressors impact animals. Particularly for those species that require consumption of energy‐dense prey, such as the common dolphin. Thus far, no uniform measure for monitoring body condition has been recommended across cetaceans, and species‐specific measures may need to be developed if employed as a population condition indicator under Descriptor 1 of the Marine Strategy Framework Directive. Here, nine morphometric body condition indices were applied to long‐term common dolphin stranding data sets originating from Ireland and the UK. We report a recent decline in the nutritional health of common dolphins in the Celtic Seas ecoregion comparing animals from 2017 to 2019 to animals from 1990 to 2006, with an increase in cases of animals dying due to starvation. Using ordinal regression trees, ventral blubber thickness (VBT) was identified as the most important index to predict nutritional status, defined at necropsy, followed by the scaled mass index (SMI). Using generalised linear models, both the VBT and SMI indices differentiated individuals that died from chronic and acute causes of death (i.e., bycatch), where animals in chronic conditions had significantly thinner VBT and lower SMI. Both significant temporal and seasonal patterns in VBT were identified, with poorer body conditions observed during the autumn and better body conditions observed during the spring, as well as an overall decline detected in VBT during the study period. While VBT was positively correlated with total body length, SMI showed the opposite trend. The VBT index is recommended for monitoring nutritional health within the species when total body length and season are considered. Further research is needed to understand the underlying causes for the observed decline, including shifts in prey availability and/or quality, to inform targeted conservation management strategies. The nutritional health of stranded common dolphins in the Celtic Seas ecoregion has recently declined, as evidenced by a decrease in nutritional status and an increase in starvation‐related deaths. Ventral blubber thickness was identified as the most reliable predictor of nutritional status when comparing various morphometric indices using ordinal regression tree analysis. We recommend using ventral blubber thickness while considering body length and seasonal variations to monitor the health of these dolphins and to inform conservation strategies.

Background Acanthocephalans of the genus Bolbosoma Porta, 1908 are trophically transmitted parasites that infect marine mammals (mostly cetaceans and less frequently pinnipeds) worldwide. There are 12 species currently considered as valid; however, most records lack information on the maturity stage of the specimens. This, coupled with the scarce phylogenetic information available, hinders a correct understanding of their patterns of host specificity, evolutionary history, and taxonomy. A particularly intriguing case is that of Bolbosoma vasculosum (Rudolphi, 1819), which has been frequently reported in odontocetes but rarely as an adult, having been suggested to be synonymous with Bolbosoma capitatum (von Linstow, 1880). Methods We used a comprehensive approach to investigate the concept of Bolbosoma . First, we conducted a bibliographic review of records of Bolbosoma spp. to clarify which are the final hosts for each species. We paid particular attention to B. vasculosum , using morphological and molecular analyses to compare it with B. capitatum . Second, we characterized the complete mitochondrial genome of Bolbosoma balaenae (Gmelin, 1790), Bolbosoma turbinella (Diesing, 1851), B. capitatum , and B. vasculosum . Then, we reconstructed the phylogenetic relationships of Bolbosoma spp. and related taxa using full mitochondrial genomes (or only cox1 when full mitogenomes were unavailable) and nuclear ribosomal genes (18S and 28S). Results Bolbosoma spp. exhibit high specificity for cetaceans, with no confirmed records of adult specimens in other host groups. Within this genus, B. vasculosum appears to be conspecific with B. capitatum based on both morphological and molecular evidence. This species shows high affinity to odontocetes, while the remaining species are specific to mysticetes. Phylogenetic analyses showed strong support for the monophyly of Bolbosoma spp., which appeared as sister taxa to Corynosoma spp. and Andracantha spp.. The resulting topology aligns with the patterns of specificity indicated by host records, revealing two distinct clades for species specific to odontocetes and mysticetes, respectively. Conclusions The phylogenetic relationships obtained support the hypothesis that the association of Bolbosoma spp. with cetaceans originated through a host-switching event from aquatic birds.

Neisseria animaloris is considered to be a commensal of the canine and feline oral cavities. It is able to cause systemic infections in animals as well as humans, usually after a biting trauma has occurred. We recovered N . animaloris from chronically inflamed bite wounds on pectoral fins and tailstocks, from lungs and other internal organs of eight harbour porpoises. Gross and histopathological evidence suggest that fatal disseminated N . animaloris infections had occurred due to traumatic injury from grey seals. We therefore conclude that these porpoises survived a grey seal predatory attack, with the bite lesions representing the subsequent portal of entry for bacteria to infect the animals causing abscesses in multiple tissues, and eventually death. We demonstrate that forensic microbiology provides a useful tool for linking a perpetrator to its victim. Moreover, N . animaloris should be added to the list of potential zoonotic bacteria following interactions with seals, as the finding of systemic transfer to the lungs and other tissues of the harbour porpoises may suggest a potential to do likewise in humans.

Assessing long‐term population health is an important feature of wildlife monitoring and is essential for understanding population resilience. Quantitative assessments of health indices are essential for effective monitoring yet they remain a challenge for cetaceans due to their highly mobile and largely cryptic nature. Quantified assessments of cetacean health typically rely on evaluating body condition, which reflects energetic reserves and nutritional status. However, this method may not capture sub‐lethal impacts or comorbidities resulting from chronic or cumulative stressors. Necropsies of stranded individuals provide unique insight into the morbidity of an individual and offer clues about the pressures an individual has faced over its lifetime, making necropsy reports a valuable source for understanding health. However, the predominantly qualitative and narrative format of necropsy reports limits their utility for systematic statistical analysis, thereby constraining their application in generating robust, population‐level inferences. Using 349 necropsy records of harbour porpoises (Phocoena phocoena ) stranded on the Scottish coastline as a case study, we developed a structured pathology database suitable for statistical analysis. The application of unsupervised and supervised machine learning techniques has revealed underlying patterns in harbour porpoise pathology. This has shown that necropsy data may provide a more comprehensive insight into health than traditional methods. We identified the respiratory and hepatic systems as explaining a high degree of variation in the data. This highlights these organ systems as priority areas for data collection and subsequent analysis. Patterns in the data revealed underlying compromised health, particularly in adult harbour porpoises, suggesting a vulnerability to additional stressors in this group. Our approach demonstrates how pathology data from necropsy reports can be used to derive population‐level health insights, offering a tool for monitoring the impacts of environmental and anthropogenic pressures on wildlife populations. Assessing long‐term health in wildlife populations remains challenging, especially for cetaceans, whose mobility and cryptic behaviour limit traditional assessments based solely on body condition. By analysing 349 necropsy records of harbour porpoises stranded along the Scottish coastline, we created a structured pathology database and applied machine learning techniques to identify patterns in organ‐specific morbidity, highlighting the respiratory and hepatic systems as key indicators of health. Our findings reveal underlying compromised health in adult harbour porpoises, suggesting reduced resilience to additional stressors. They demonstrate that necropsy data can provide robust, population‐level insights into the impacts of environmental and anthropogenic pressures on wildlife.