Population genomics of the white-beaked dolphin (Lagenorhynchus albirostris): Implications for conservation amid climate-driven range shifts

Climate change is rapidly affecting species distributions across the globe, particularly in the North Atlantic. For highly mobile and elusive cetaceans, the genetic data needed to understand population dynamics are often scarce. Cold-water obligate species such as the white-beaked dolphin (Lagenorhynchus albirostris) face pressures from habitat shifts due to rising sea surface temperatures in addition to other direct anthropogenic threats. Unravelling the genetic connectivity between white-beaked dolphins across their range is needed to understand the extent to which climate change and anthropogenic pressures may impact species-wide genetic diversity and identify ways to protect remaining habitat. We address this by performing a population genomic assessment of white-beaked dolphins using samples from much of their contemporary range. We show that the species displays significant population structure across the North Atlantic at multiple scales. Analysis of contemporary migration rates suggests a remarkably high connectivity between populations in the western North Atlantic, Iceland and the Barents Sea, while two regional populations in the North Sea and adjacent UK and Irish waters are highly differentiated from all other clades. Our results have important implications for the conservation of white-beaked dolphins by providing guidance for the delineation of more appropriate management units and highlighting the risk that local extirpation may have on species-wide genetic diversity. In a broader context, this study highlights the importance of understanding genetic structure of all species threatened with climate change-driven range shifts to assess the risk of loss of species-wide genetic diversity.

Microstructural differences in the osteochondral unit of terrestrial and aquatic mammals

During evolution, animals have returned from land to water, adapting with morphological modifications to life in an aquatic environment. We compared the osteochondral units of the humeral head of marine and terrestrial mammals across species spanning a wide range of body weights, focusing on microstructural organization and biomechanical performance. Aquatic mammals feature cartilage with essentially random collagen fiber configuration, lacking the depth-dependent, arcade-like organization characteristic of terrestrial mammalian species. They have a less stiff articular cartilage at equilibrium with a significantly lower peak modulus, and at the osteochondral interface do not have a calcified cartilage layer, displaying only a thin, highly porous subchondral bone plate. This totally different constitution of the osteochondral unit in aquatic mammals reflects that accommodation of loading is the primordial function of the osteochondral unit. Recognizing the crucial importance of the microarchitecture-function relationship is pivotal for understanding articular biology and, hence, for the development of durable functional regenerative approaches for treatment of joint damage, which are thus far lacking.

Harbor Porpoise Deaths Associated with Erysipelothrix rhusiopathiae, the Netherlands, 2021

In August 2021, a large-scale mortality event affected harbor porpoises (Phocoena phocoena) in the Netherlands. Pathology and ancillary testing of 22 animals indicated that the most likely cause of death was Erysipelothrix rhusiopathiae infection. This zoonotic agent poses a health hazard for cetaceans and possibly for persons handling cetacean carcasses.

Spontaneous neoplasms in harbour porpoises Phocoena phocoena

Harbour porpoises are widely distributed in the North Atlantic and represent the most abundant cetacean species in the North and Baltic Seas. Spontaneous neoplasms are relatively rarely reported in cetaceans, and only little is known about neoplasia in harbour porpoises. Thus, archival material was reviewed for spontaneous neoplasms in harbour porpoises recorded during post-mortem examinations between 1999 and 2018. Neoplasms were identified in 7 adult porpoises: 6 animals originating from the North and Baltic Seas and investigated as part of German and Dutch systematic health monitoring programs, and 1 porpoise from Greenlandic waters. The tumours were of different histogenetic origins and further characterised by histology and immunohistochemistry. One individual had a neoplasia in the digestive tract (adenocarcinoma, n = 1); 4 animals, in the genital tract (Sertoli cell tumour, n = 1; genital leiomyoma/fibroleiomyoma, n = 3); and 2 porpoises, in endocrine organs (adrenal adenoma, n = 2). This is the first report of an adenocarcinoma in the liver, a testicular Sertoli cell tumour and adrenocortical adenomas in harbour porpoises. The cause of the tumorigenesis in examined cases remains undetermined. The involvement of endogenous factors, including mutation of cell cycle regulating genes, such as the tumour-suppressor gene p53, cannot be ruled out. The aetiopathogenetic significance of exogenous factors, such as infectious agents like liver flukes or anthropogenic factors, including persistent organic pollutants, should be the subject of future investigations.

Post-Mortem Computed Tomography Pulmonary Findings in Harbor Porpoises (Phocoena phocoena)

Simple Summary

The use of cross-sectional imaging techniques to examine the cause of death and health status of deceased animals is increasing in both veterinary and wildlife conservation programs, including species of whales and dolphins. Lung disease is common in harbor porpoises (Phocoena phocoena), a small whale species that regularly washes up on the coast in North Sea-bordering countries. This study aimed to describe lung changes visible in computed tomographic (CT) images of recently deceased harbor porpoises before pathological dissection was performed, including comparison of these two examination methods. Despite frequently visible signs of body decomposition, several lung abnormalities (collapsed lung, fluid in the airways, lung mineralization) were more often seen on the CT images. In general, lung changes could be described in more detail compared to gross dissection. CT images of lungs of recently deceased harbor porpoises can therefore be used to guide gross dissection, leading to more specific findings and potentially a more complete understanding of the circumstances leading to the death of the porpoise, assessment of the population, and ultimately, ecosystem health.

Abstract

The application of whole-body post-mortem computed tomography (PMCT) in veterinary and wildlife post-mortem research programs is advancing. A high incidence of pulmonary pathology is reported in the harbor porpoise (Phocoena phocoena). In this study, the value of PMCT focused on pulmonary assessment is evaluated. The objectives of this study were to describe pulmonary changes as well as autolytic features detected by PMCT examination and to compare those findings with conventional necropsy. Retrospective evaluation of whole-body PMCT images of 46 relatively fresh harbor porpoises and corresponding conventional necropsy reports was carried out, with a special focus on the respiratory tract. Common pulmonary PMCT findings included: moderate (24/46) to severe (19/46) increased pulmonary soft tissue attenuation, severe parasite burden (17/46), bronchial wall thickening (30/46), and mild autolysis (26/46). Compared to conventional necropsy, PMCT more frequently identified pneumothorax (5/46 vs. none), tracheal content (26/46 vs. 7/46), and macroscopic pulmonary mineralization (23/46 vs. 11/46), and provided more information of the distribution of pulmonary changes. These results indicate that PMCT adds information on pulmonary assessment and is a promising complementary technique for necropsy, despite the frequent presence of mild autolytic features.

Reconstructing the diet, trophic level and migration pattern of mysticete whales based on baleen isotopic composition

Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of δ13C and δ15N values from bulk baleen have been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here, we apply analysis of δ15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.7-3.8 versus 3-3.2, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. Phenylanine δ15N values confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine δ15N values suggested physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.

Polluted porpoises: Generational transfer of organic contaminants in harbour porpoises from the southern North Sea

Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and hexachlorobenzene (HCB), bioaccumulate in marine ecosystems. Top predators contain high levels of POPs in their lipid-rich tissues, which may result in adverse effects on their reproductive, immune and endocrine functions. Harbour porpoises (Phocoena phocoena) are among the smallest of cetaceans and live under high metabolic demand, making them particularly vulnerable to environmental pressures. Using samples from individuals of all maturity classes and sexes stranded along the southern North Sea (n = 121), we show the generational transfer of PCBs, PBDEs and HCB from adults to foetuses. Porpoise placentas contained 1.3-8.2 mg/kg lipid weight (lw) Sum-17PCB, <dl-0.08 mg/kg lw Sum-17PBDE and 0.14-0.16 mg/kg lw HCB, which were similar to concentrations in foetus blubber. Contaminant levels increased significantly after birth through suckling. Milk samples contained 0.20-33.8 mg/kg lw Sum-17PCB, 0.002-0.51 mg/kg lw Sum-17PBDE and 0.03-0.21 mg/kg lw HCB. Especially lower halogenated and more toxic contaminants were transferred to calves, exposing them to high levels of contaminants early in life. Of all animals included in this study, 38.5% had PCB concentrations exceeding a threshold level for negative health effects (>9 mg/kg lw). This was particularly true for adult males (92.3% >9 mg/kg lw), while adult females had relatively low PCB levels (10.5% >9 mg/kg lw) due to offloading. Nutritional stress led to higher offloading in the milk, causing a greater potential for toxicity in calves of nutritionally stressed females. No correlation between PCB concentration and parasite infestation was detected, although the probability of a porpoise dying due to infectious disease or debilitation increased with increasing PCB concentrations. Despite current regulations to reduce pollution, these results provide further evidence of potential health effects of POPs on harbour porpoises of the southern North Sea, which may consequently increase their susceptibility to other pressures.

Evidence of Hearing Loss and Unrelated Toxoplasmosis in a Free-Ranging Harbour Porpoise (Phocoena phocoena)

Simple Summary

Evidence of hearing impairment was identified in a female harbour porpoise (Phocoena phocoena) on the basis of inner ear analysis. The animal live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. Ultrastructural examination of the inner ear revealed evidence of sensory cell loss, which is compatible with noise exposure. In addition, histopathology also revealed multifocal necrotising protozoal encephalitis. A diagnosis of toxoplasmosis was confirmed by positive staining of tissue with anti-Toxoplasma gondii antibodies; however, T. gondii tachyzoites were not observed histologically in any of the examined tissues. This is the first case of presumptive noise-induced hearing loss and demonstration of T. gondii cysts in the brain of a free-ranging harbour porpoise from the North Sea.

Abstract

Evidence of hearing impairment was identified in a harbour porpoise (Phocoena phocoena) on the basis of scanning electron microscopy. In addition, based on histopathology and immunohistochemistry, there were signs of unrelated cerebral toxoplasmosis. The six-year old individual live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. The most significant gross lesion was multifocal necrosis and haemorrhage of the cerebrum. Histopathology of the brain revealed extensive necrosis and haemorrhage in the cerebrum with multifocal accumulations of degenerated neutrophils, lymphocytes and macrophages, and perivascular lymphocytic cuffing. The diagnosis of cerebral toxoplasmosis was confirmed by positive staining of protozoa with anti-Toxoplasma gondii antibodies. Tachyzoites were not observed histologically in any of the examined tissues. Ultrastructural evaluation of the inner ear revealed evidence of scattered loss of outer hair cells in a 290 µm long segment of the apical turn of the cochlea, and in a focal region of ~ 1.5 mm from the apex of the cochlea, which was compatible with noise-induced hearing loss. This is the first case of concurrent presumptive noise-induced hearing loss and toxoplasmosis in a free-ranging harbour porpoise from the North Sea.

Whale lice (Isocyamus deltobranchium & Isocyamus delphinii; Cyamidae) prevalence in odontocetes off the German and Dutch coasts - morphological and molecular characterization and health implications

Whale lice (Cyamidae; Amphipoda) are ectoparasitic crustaceans adapted to the marine environment with cetaceans as their host. There are few reports of cyamids occurring in odontocetes from the North Sea, and long-term studies are lacking. Marine mammal health was monitored along the German and Dutch coasts in the past decades, with extensive post mortem investigations conducted. The aim of this study was to analyse archived ectoparasite samples from stranded cetaceans from the North Sea (2010-2019), to determine species, prevalence and impact of ectoparasite infection. Ectoparasites were found on two cetacean species - harbour porpoises (Phocoena phocoena), as the most abundant cetacean species in the North Sea, and on a pilot whale (Globicephala melas), as a rare species here. Prevalence of ectoparasitic crustaceans in cetaceans was low: 7.6% in porpoises stranded in the Netherlands (n = 608) and 1.6% in porpoises stranded in Germany (n = 122). All whale lice infections were found on hosts with skin lesions characterised by ulcerations. Morphological investigations revealed characteristic differences between the cyamid species Isocyamus (I.) delphinii and I. deltobranchium identified. Isocyamus deltobranchium was determined in all infected harbour porpoises. I. delphinii was identified on only the pilot whale. Molecular analyses showed 88% similarity of mDNA COI sequences of I. delphinii with I. deltobranchium supporting them as separate species. Phylogenetic analyses of additional gene loci are required to fully assess the diversity and exchange of whale lice species between geographical regions as well as host specificity. Differing whale lice prevalences in porpoises stranded in the Netherlands and Germany could indicate a difference in severity of skin lesions between these areas. It should be further investigated if more inter- or intraspecific contact, e.g., due to a higher density of porpoises or contact with other cetaceans, or a poorer health status of porpoises in the southern North Sea could explain these differences.

Cochlear apical morphology in toothed whales: Using the pairing hair cell-Deiters' cell as a marker to detect lesions

The apex or apical region of the cochlear spiral within the inner ear encodes for low-frequency sounds. The disposition of sensory hair cells on the organ of Corti is largely variable in the apical region of mammals, and it does not necessarily follow the typical three-row pattern of outer hair cells (OHCs). As most underwater noise sources contain low-frequency components, we expect to find most lesions in the apical region of the cochlea of toothed whales, in cases of permanent noise-induced hearing loss. To further understand how man-made noise might affect cetacean hearing, there is a need to describe normal morphological features of the apex and document interspecific anatomic variations in cetaceans. However, distinguishing between apical normal variability and hair cell death is challenging. We describe anatomical features of the organ of Corti of the apex in 23 ears from five species of toothed whales (harbor porpoise Phocoena phocoena, spinner dolphin Stenella longirostris, pantropical spotted dolphin Stenella attenuata, pygmy sperm whale Kogia breviceps, and beluga whale Delphinapterus leucas) by scanning electron microscopy and immunofluorescence. Our results showed an initial region where the lowest frequencies are encoded with two or three rows of OHCs, followed by the typical configuration of three OHC rows and three rows of supporting Deiters' cells. Whenever two rows of OHCs were detected, there were usually only two corresponding rows of supporting Deiters' cells, suggesting that the number of rows of Deiters' cells is a good indicator to distinguish between normal and pathological features.

What a stranded whale with scoliosis can teach us about human idiopathic scoliosis

Scoliosis is a deformation of the spine that may have several known causes, but humans are the only mammal known to develop scoliosis without any obvious underlying cause. This is called 'idiopathic' scoliosis and is the most common type. Recent observations showed that human scoliosis, regardless of its cause, has a relatively uniform three-dimensional anatomy. We hypothesize that scoliosis is a universal compensatory mechanism of the spine, independent of cause and/or species. We had the opportunity to study the rare occurrence of scoliosis in a whale (Balaenoptera acutorostrata) that stranded in July 2019 in the Netherlands. A multidisciplinary team of biologists, pathologists, veterinarians, taxidermists, radiologists and orthopaedic surgeons conducted necropsy and imaging analysis. Blunt traumatic injury to two vertebrae caused an acute lateral deviation of the spine, which had initiated the development of compensatory curves in regions of the spine without anatomical abnormalities. Three-dimensional analysis of these compensatory curves showed strong resemblance with different types of human scoliosis, amongst which idiopathic. This suggests that any decompensation of spinal equilibrium can lead to a rather uniform response. The unique biomechanics of the upright human spine, with significantly decreased rotational stability, may explain why only in humans this mechanism can be induced relatively easily, without an obvious cause, and is therefore still called 'idiopathic'.

Challenges in the Assessment of Bycatch: Postmortem Findings in Harbor Porpoises (Phocoena phocoena) Retrieved From Gillnets

Bycatch is considered one of the most significant threats affecting cetaceans worldwide. In the North Sea, bottom-set gillnets are a specific risk for harbor porpoises (Phocoena phocoena). Methods to estimate bycatch rates include on-board observers, remote electronic monitoring, and fishermen voluntarily reporting; none of these are systematically conducted. Additionally, necropsies of stranded animals can provide insights into bycatch occurrence and health status of individuals. There are, however, uncertainties when it comes to the assessment of bycatch in stranded animals, mainly due to the lack of diagnostic tools specific for underwater entrapment. We conducted a literature review to establish criteria that aid in the assessment of bycatch in small cetaceans, and we tested which of these criteria applied to harbor porpoises retrieved from gillnets in the Netherlands (n = 12). Twenty-five criteria were gathered from literature. Of these, "superficial incisions," "encircling imprints," and "recent ingestion of prey" were observed in the vast majority of our confirmed bycatch cases. Criteria like "pulmonary edema," "pulmonary emphysema," and "organ congestion" were also frequently observed, although considered unspecific as an indicator of bycatch. Notably, previously mentioned criteria as "favorable health status," "absence of disease," or "good nutritional condition" did not apply to the majority of our bycaught porpoises. This may reflect an overall reduced fitness of harbor porpoises inhabiting the southern North Sea or a higher chance of a debilitated porpoise being bycaught, and could result in an underestimation of bycatch rates when assessing stranded animals.

Vertebral pattern variation in the North Sea harbor porpoise (Phocoena phocoena) by computed tomography

Vertebral series in the harbor porpoise (Phocoena phocoena) include cervical, thoracic, lumbar, and caudal. In contrast to studying skeletons from museums, in which small bones can be missed, evaluation of full body computed tomography (CT) scans provides an overview of the vertebral column, while maintaining interrelationship of all structures. The aim of this study was to document variations in vertebral patterning of the harbor porpoise via evaluation of CT images of intact stranded harbor porpoises. The harbor porpoises were divided into age classes, based on developmental stage of reproductive organs on postmortem examination and closure of proximal humeral physis on CT. Numbers of vertebrae per series, fusion state of the syncervical, type of first hemal arch, number of double articulating ribs, and floating ribs were recorded based on CT images. Included in the study were 48 harbor porpoises (27 males and 21 females), which were divided in two age classes (27 immatures and 21 adults). Total vertebral count varied from 63 to 68 with vertebral formula range C7T12‐14L12‐16Cd29‐33. Twenty‐five different vertebral formulas were found, of which C7T13L14Ca30 was the most common (n = 8, 17%). Thoracic vertebrae with six, seven, or eight double articulating ribs and zero, one, or two vertebrae with floating ribs were seen. Four different fusion states of the syncervical and four types of hemal arches were recognized. This study showed a great variation in vertebral patterning in the harbor porpoise, with homeotic and meristic variation in the thoracic, lumbar, and caudal vertebral series.

Anisakid nematode species identification in harbour porpoises (Phocoena phocoena) from the North Sea, Baltic Sea and North Atlantic using RFLP analysis

Harbour porpoises (Phocoena phocoena) are the only native cetacean species in the German North and Baltic Seas and the final host of Anisakis (A.) simplex, which infects their first and second gastric compartments and may cause chronic ulcerative gastritis. Anisakis simplex belongs to the family Anisakidae (Ascaridoidea, Rhabditida) as well as the phocine gastric nematode species Pseudoterranova (P.) decipiens and Contracaecum (C.) osculatum. These nematode species are the main causative agents for the zoonosis anisakidosis. The taxonomy of these genus with life cycles including crustaceans and commercially important fish is complex because of the formation of sibling species. Little is known about anisakid species infecting porpoises in the study area. Mature nematodes and larval stages are often identifiable only by molecular methods due to high morphological and genetic similarity. The restriction fragment length polymorphism (RFLP) method is an alternative to sequencing and was applied to identify anisakid nematodes found in harbour porpoises from the North Sea, Baltic Sea and North Atlantic to species level for the first time. In the study areas, five gastric nematodes from different harbour porpoise hosts were selected to be investigated with restriction enzymes HinfI, RsaI and HaeIII, which were able to differentiate several anisakid nematode species by characteristic banding patterns. Anisakis simplex s. s. was the dominant species found in the North Sea and Baltic porpoises, identified by all three restriction enzymes. Additionally, a hybrid of A. simplex s. s. and A. pegreffii was determined by HinfI in the North Sea samples. Within the North Atlantic specimens, A. simplex s. s., P. decipiens s. s. and Hysterothylacium (H.) aduncum were identified by all enzymes. This demonstrates the value of the RFLP method and the chosen restriction enzymes for the species identification of a broad variety of anisakid nematodes affecting the health of marine mammals.

Echolocating Whales and Bats Express the Motor Protein Prestin in the Inner Ear: A Potential Marker for Hearing Loss

Prestin is an integral membrane motor protein located in outer hair cells of the mammalian cochlea. It is responsible for electromotility and required for cochlear amplification. Although prestin works in a cycle-by-cycle mode up to frequencies of at least 79 kHz, it is not known whether or not prestin is required for the extreme high frequencies used by echolocating species. Cetaceans are known to possess a prestin coding gene. However, the expression and distribution pattern of the protein in the cetacean cochlea has not been determined, and the contribution of prestin to echolocation has not yet been resolved. Here we report the expression of the protein prestin in five species of echolocating whales and two species of echolocating bats. Positive labeling in the basolateral membrane of outer hair cells, using three anti-prestin antibodies, was found all along the cochlear spiral in echolocating species. These findings provide morphological evidence that prestin can have a role in cochlear amplification in the basolateral membrane up to 120–180 kHz. In addition, labeling of the cochlea with a combination of anti-prestin, anti-neurofilament, anti-myosin VI and/or phalloidin and DAPI will be useful for detecting potential recent cases of noise-induced hearing loss in stranded cetaceans. This study improves our understanding of the mechanisms involved in sound transduction in echolocating mammals, as well as describing an optimized methodology for detecting cases of hearing loss in stranded marine mammals.

Pathological Findings in White-Beaked Dolphins (Lagenorhynchus albirostris) and Atlantic White-Sided Dolphins (Lagenorhynchus acutus) From the South-Eastern North Sea

In the North Sea, white-beaked dolphins (Lagenorhynchus albirostris) occur regularly and are the second most common cetacean in the area, while their close relative, the Atlantic white-sided dolphin (Lagenorhynchus acutus), prefers the deeper waters of the northern North Sea and adjacent Atlantic Ocean. Though strandings of both species have occurred regularly in the past three decades, they have decreased in the southern North Sea during the last years. Studies describing necropsy findings in stranded Lagenorhynchus spp. are, to date, still scarce, while information gained through post-mortem examinations may reveal valuable information about underlying causes of this decline, including age structure and the reproduction status. Therefore, we retrospectively assessed and compared the necropsy results from fresh Lagenorhynchus spp. stranded along the southeastern North Sea between 1990 and 2019. A full necropsy was performed on 24 white-beaked dolphins and three Atlantic white-sided dolphins from the German and Dutch coast. Samples of selected organs were taken for histopathological, bacteriological, mycological, parasitological and virological examinations. The most common post-mortem findings were emaciation, gastritis and pneumonia. Gastritis and ulceration of the stomach was often associated with an anisakid nematode infection. Pneumonia was most likely caused by bacterial infections. Encephalitis was observed in three animals and morbillivirus antigen was detected immunohistochemically in one case. Although the animal also showed pneumonic lesions, virus antigen was only found in the brain. Parasitic infections mainly affected the gastro-intestinal tract. Lungworm infections were only detected in two cases and no associations with pathological alterations were observed. Stenurus spp. were identified in two of three cases of parasitic infections of the ears. Twelve of the 26 white-beaked dolphins stranded in Germany were found between 1993 and 1994, but there was no evidence of epizootic disease events or mass strandings during the monitored period.

After the bite: bacterial transmission from grey seals (Halichoerus grypus) to harbour porpoises (Phocoena phocoena)

Recent population growth of the harbour porpoise (Phocoena phocoena), grey seal (Halichoerus grypus) and common seal (Phoca vitulina) in the North Sea has increased potential interaction between these species. Grey seals are known to attack harbour porpoises. Some harbour porpoises survive initially, but succumb eventually, often showing severely infected skin lesions. Bacteria transferred from the grey seal oral cavity may be involved in these infections and eventual death of the animal. In humans, seal bites are known to cause severe infections. In this study, a 16S rRNA-based microbiome sequencing approach is used to identify the oral bacterial diversity in harbour porpoises, grey seals and common seals; detect the potential transfer of bacteria from grey seals to harbour porpoises by biting and provide insights in the bacteria with zoonotic potential present in the seal oral cavity. β-diversity analysis showed that 12.9% (4/31) of the harbour porpoise skin lesion microbiomes resembled seal oral microbiomes, while most of the other skin lesion microbiomes also showed seal-associated bacterial species, including potential pathogens. In conclusion, this study shows that bacterial transmission from grey seals to harbour porpoises by biting is highly likely and that seal oral cavities harbour many bacterial pathogens with zoonotic potential.

Forensic microbiology reveals that Neisseria animaloris infections in harbour porpoises follow traumatic injuries by grey seals

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.

Inter-individual differences in contamination profiles as tracer of social group association in stranded sperm whales

Ecological and physiological factors lead to different contamination patterns in individual marine mammals. The objective of the present study was to assess whether variations in contamination profiles are indicative of social structures of young male sperm whales as they might reflect a variation in feeding preferences and/or in utilized feeding grounds. We used a total of 61 variables associated with organic compounds and trace element concentrations measured in muscle, liver, kidney and blubber gained from 24 sperm whales that stranded in the North Sea in January and February 2016. Combining contaminant and genetic data, there is evidence for at least two cohorts with different origin among these stranded sperm whales; one from the Canary Island region and one from the northern part of the Atlantic. While genetic data unravel relatedness and kinship, contamination data integrate over areas, where animals occured during their lifetime. Especially in long-lived animals with a large migratory potential, as sperm whales, contamination data may carry highly relevant information about aggregation through time and space.

Plastic ingestion by harbour porpoises Phocoena phocoena in the Netherlands: Establishing a standardised method

Stomach contents of harbour porpoises (Phocoena phocoena) collected in the Netherlands between 2003 and 2013 were inspected for the presence of plastic and other man-made litter. In 654 stomach samples the frequency of occurrence of plastic litter was 7% with less than 0.5% additional presence of non-synthetic man-made litter. However, we show that when a dedicated standard protocol for the detection of litter is followed, a considerably higher percentage (15% of 81 harbour porpoise stomachs from the period 2010-2013) contained plastic litter. Results thus strongly depended on methods used and time period considered. Occurrence of litter in the stomach was correlated to the presence of other non-food remains like stones, shells, bog-wood, etc., suggesting that litter was often ingested accidentally when the animals foraged close to the bottom. Most items were small and were not considered to have had a major health impact. No evident differences in ingestion were found between sexes or age groups, with the exception that neonates contained no litter. Polyethylene and polypropylene were the most common plastic types encountered. Compared to earlier literature on the harbour porpoise and related species, our results suggest higher levels of ingestion of litter. This is largely due to the lack of dedicated protocols to investigate marine litter ingestion in previous studies. Still, the low frequency of ingestion, and minor number and mass of litter items found in harbour porpoises in the relatively polluted southern North Sea indicates that the species is not a strong candidate for annual monitoring of marine litter trends under the EU marine strategy framework directive. However, for longer-term comparisons and regional differences, with proper dedicated protocols applied, the harbour porpoise has specific use in quantifying litter presence in the, for that specific objective, poorly studied benthic marine habitat.

Quantifying parasite presence in relation to biological parameters of harbour porpoises Phocoena phocoena stranded on the Dutch coast

Harbour porpoises are often found to be infected by endoparasites in several organs including the lungs and stomach as well as the heart, liver and ears. Nevertheless there is still little knowledge about the impact, ecology, transmission, and virulence of these parasitic infections. Here, we profile the presence of parasites in 4 frequently infected organs (lungs, stomach, liver and ears) in relation to biological parameters of harbour porpoises stranded along the Dutch coastline between December 2008 and December 2013. We found that parasites were common, with prevalence of 68% in lungs, 74.4% in ears, 26% in stomach and 23.5% in liver. We used generalised linear models to further quantify parasite presence in relation to biological data gathered during necropsy (sex, body length and nutritive condition). Body length (used as a proxy for age) was significant in explaining parasite presence for all organs with increasing probability of having the parasite with increasing body length. For the parasitic infections in the ears and stomach the nutritive condition was an additional significant factor, with a higher probability of parasite presence in porpoises in a poorer nutritive condition. The results of this study can be used as a baseline for assessing parasite presence in harbour porpoises and are a first step towards linking parasite infections to basic biological data gathered during necropsy.

Parasites in the inner ear of harbour porpoise: cases from the North and Baltic Seas

Peribullar sinuses of harbour porpoises Phocoena phocoena are parasitized with high prevalence by the nematode Stenurus minor. The effect of S. minor on the hearing ability of this species is still undetermined. Here, we review the occurrence of S. minor in the inner ear of harbour porpoises recovered from strandings in the North and Baltic Seas. In particular, we present the results from ears collected in German and Danish waters from 2002 to 2016 and from Dutch waters from 2010 to 2016. While the prevalence of S. minor in pterygoid and peribullar sinuses and tympanic cavity was high in harbour porpoises (66.67% in our cases), its prevalence in the cochlea was rare. Only 1 case out of 129 analysed by either histology, electron microscopy or immunofluorescence showed the presence of a nematode parasite morphologically consistent with S. minor at the most basal portion of the right cochlea. This individual also had severe haemorrhage along the right cochlear spiral, which was likely caused by ectopic S. minor migration. Although this animal might have had impaired hearing in the right ear, it was otherwise in good body condition with evidence of recent feeding. These findings highlight the need to study the effect of parasites on hearing, and other pathological changes that might impair appropriate processing of acoustic information.

Large amounts of marine debris found in sperm whales stranded along the North Sea coast in early 2016

30 sperm whales (Physeter macrocephalus) stranded along the coasts of the North Sea between January and February 2016. The gastro-intestinal tracts of 22 of the carcasses were investigated. Marine debris including netting, ropes, foils, packaging material and a part of a car were found in nine of the 22 individuals. Here we provide details about the findings and consequences for the animals. While none of the items was responsible for the death of the animal, the findings demonstrate the high level of exposure to marine debris and associated risks for large predators, such as the sperm whale.

Fatal Asphyxiation in Two Long-Finned Pilot Whales (Globicephala melas) Caused by Common Soles (Solea solea)

Long-finned pilot whales (Globicephala melas) are rare visitors to the southern North Sea, but recently two individual strandings occurred on the Dutch coast. Both animals shared the same, unusual cause of death: asphyxiation from a common sole (Solea solea) stuck in their nasal cavity. This is a rare cause of death in cetaceans. Whilst asphyxiation has been reported in smaller odontocetes, there are no recent records of this occurring in Globicephala species. Here we report the stranding, necropsy and diet study results as well as discuss the unusual nature of this phenomenon. Flatfish are not a primary prey species for pilot whales and are rarely eaten by other cetaceans, such as harbour porpoises (Phocoena phocoena), in which there are several reports of asphyxiation due to airway obstruction by soles. This risk may be due to the fish’s flexible bodies which can enter small cavities either actively in an attempt to escape or passively due to the whale ‘coughing’ or ‘sneezing’ to rid itself of the blockage of the trachea. It is also possible that the fish enter the airways whilst the whale is re-articulating the larynx after trying to ingest large, oddly shaped prey. It is unlikely that the soles entered the airways after the death of the whales and we believe therefore that they are responsible for the death of these animals.

Identification of a novel gammaherpesvirus associated with (muco)cutaneous lesions in harbour porpoises (Phocoena phocoena)

Herpesviruses infect a wide range of vertebrates, including toothed whales of the order Cetacea. One of the smallest toothed whales is the harbour porpoise (Phocoena phocoena), which is widespread in the coastal waters of the northern hemisphere, including the North Sea. Here, we describe the detection and phylogenetic analysis of a novel gammaherpesvirus associated with mucocutaneous and skin lesions in stranded harbour porpoises along the Dutch coast, tentatively designated phocoenid herpesvirus 1 (PhoHV1). Phylogenetically, PhoHV1 forms a monophyletic clade with all other gammaherpesviruses described in toothed whales (Odontoceti) to date, suggesting a common evolutionary origin.

Exposing the grey seal as a major predator of harbour porpoises

Harbour porpoises (Phocoena phocoena) stranding in large numbers around the southern North Sea with fatal, sharp-edged mutilations have spurred controversy among scientists, the fishing industry and conservationists, whose views about the likely cause differ. The recent detection of grey seal (Halichoerus grypus) DNA in bite marks on three mutilated harbour porpoises, as well as direct observations of grey seal attacks on porpoises, have identified this seal species as a probable cause. Bite mark characteristics were assessed in a retrospective analysis of photographs of dead harbour porpoises that stranded between 2003 and 2013 (n = 1081) on the Dutch coastline. There were 271 animals that were sufficiently fresh to allow macroscopic assessment of grey seal-associated wounds with certainty. In 25% of these, bite and claw marks were identified that were consistent with the marks found on animals that had tested positive for grey seal DNA. Affected animals were mostly healthy juveniles that had a thick blubber layer and had recently fed. We conclude that the majority of the mutilated harbour porpoises were victims of grey seal attacks and that predation by this species is one of the main causes of death in harbour porpoises in The Netherlands. We provide a decision tree that will help in the identification of future cases of grey seal predation on porpoises.

Anisakis spp. induced granulomatous dermatitis in a harbour porpoise Phocoena phocoena and a bottlenose dolphin Tursiops truncatus

Cetaceans are well known definitive hosts of parasitic nematodes of the genus Anisakis (Nematoda: Anisakidae). Anisakid nematodes are also a health hazard for humans, potentially causing gastrointestinal infections or allergic reactions following the consumption of infected fish. In marine mammals, the nematodes develop from third-stage larvae to adults in the stomachs. In the first (or fore-) stomach, these parasites are typically associated with mucosal ulceration; parasites have not been identified in other organs. Two small cetaceans, a bottlenose dolphin Tursiops truncatus and a harbour porpoise Phocoena phocoena, presented marked gastric A. simplex infection, as well as chronic granulomatous and ulcerative dermatitis with intralesional nematodes, bordered by epithelial hyperplasia. Nematodes in the skin of the bottlenose dolphin were morphologically similar to Anisakis spp. Morphology of the parasitic remnants in the skin lesion of the harbour porpoise was indistinct, but molecular identification confirmed the presence of A. simplex. This is the first report of Anisakis spp. infection in the skin of marine mammals.