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Post-mortem research on porpoises (Phocoena phocoena) from Dutch waters, 2022. Biological data, health status and causes of death. This annual report presents the results of post-mortem examinations of beached harbour porpoises in 2022. One of the main objectives of the research is to quantify human-induced causes of death. In 2022, 57 dead harbour porpoises were examined: 31 males and 26 females, comprising 18 adults, 27 juveniles and 12 neonates. In addition two male foetuses were examined. Most of the examined harbour porpoises died as a result of infectious diseases (40.4%) and grey seal attacks (24.6%). Bycatch was the most likely cause of death for six porpoises (10.5%) and seven other porpoises died following trauma of unclear origin (12.3%). In dit jaarrapport worden de resultaten gepresenteerd van pathologisch onderzoek aan gestrande bruinvissen in 2022. Eén van de hoofddoelen van het onderzoek is het kwantificeren van sterfte van bruinvissen door menselijk toedoen. In 2022 zijn 57 dode bruinvissen onderzocht: 31 mannelijke en 26 vrouwelijke, waarvan 18 volwassen, 27 juveniel en 12 neonaat. Er werden daarnaast twee mannelijke foetussen aangetroffen, onderzocht en bemonsterd. De meeste van de onderzochte bruinvissen stierven door infectieziekten (40,4%) en grijzezeehondaanvallen (24,6%). Bijvangst was de meest waarschijnlijke doodsoorzaak van zes bruinvissen (10,5%). Zeven andere bruinvissen stierven als gevolg van trauma door onduidelijke oorsprong (12,3%).

This annual report presents the results of post-mortem examinations of stranded harbour porpoises in 2021. One of the main objectives of the research is to quantify human-induced causes of death. In 2021, 54 dead harbour porpoises were examined: 35 males and 19 females, comprising 24 adults, 23 juveniles and 7 neonates. In addition three foetuses found, examined and sampled. Most of the examined harbour porpoises died as a result of infectious diseases (39%) and grey seal attacks (20%). Bycatch was the most likely cause of death of 7 porpoises (13%) and 5 other porpoises died following trauma of unclear origin (9%). In dit jaarrapport worden de resultaten gepresenteerd van pathologisch onderzoek aan gestrande bruinvissen in 2021. Eén van de hoofddoelen van het onderzoek is het kwantificeren van sterfte van bruinvissen door menselijk toedoen. In 2021 zijn 54 dode bruinvissen onderzocht: 35 mannelijke en 19 vrouwelijke, waarvan 24 volwassen, 23 juveniel en 7 neonaten. Er werden daarnaast 3 foetussen gevonden, onderzocht en bemonsterd. De meeste van de onderzochte bruinvissen waren gestorven door infectieziekten (39%) en grijzezeehondaanvallen (20%). Bijvangst was de meest waarschijnlijke doodsoorzaak van 7 bruinvissen (13%). 5 andere bruinvissen stierven als gevolg van trauma door onduidelijke oorsprong (9%).

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.

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’.

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.

This annual report presents the results of post-mortem examinations of porpoises in 2019. One of the main objectives of the research is to quantify human-induced causes of death. In 2019, 57 dead harbour porpoises were examined: 31 males and 26 females, 22 adults, 24 juveniles and 11 neonates. There were an additional six foetuses found. Most of the examined harbour porpoises died as a result of infectious diseases (30%) and grey seal attacks (21%), followed by bycatch (11%). In dit jaarrapport worden de resultaten gepresenteerd van pathologisch onderzoek aan bruinvissen in 2019. Eén van de hoofddoelen van het onderzoek is het kwantificeren van sterfte van bruinvissen door menselijk toedoen. In 2019 zijn 57 dode bruinvissen onderzocht; 31 mannelijke en 26 vrouwelijke, 22 volwassen, 24 juveniel en 11 neonaat. Er werden daarnaast 6 foetussen gevonden. De meeste van de onderzochte bruinvissen waren gestorven door infectieziekten (30%) en grijze zeehond aanvallen (21%), gevolgd door bijvangst (11%).

Studies on the occurrence of fungal communities in the marine environment are still scarce, but mycotic infections in cetaceans are increasingly reported. Fungal disease following infection with Aspergillus species is most frequently reported, with the respiratory tract commonly affected in cetaceans and other taxa, like humans and birds. Infection with Aspergillus spp. is dependent on the characteristics of the fungus as well as the hosts immune status, with dissemination into other organs being relatively common. Along the southern North Sea, harbor porpoise (Phocoena phocoena) strandings increased significantly since 2005 and necropsies to determine causes of death have been conducted since 2008. Here we describe the post-mortem findings in stranded, free-ranging harbor porpoises on the Dutch coast which were diagnosed with fungal disease, to determine the prevalence of mycotic infections, and to compare them to those described in other species. A total of 18/754 (2.4%) harbor porpoises showed lesions compatible with localized or disseminated fungal disease as confirmed by histological examination. The respiratory tract was most commonly affected (67%), followed by the central nervous system (CNS, 33%), and auditory system (AS, 17%). Aspergillosis was confirmed for 11/18, by fungal growth (as A. fumigatus species complex, n = 9) and PCR (as Aspergillus spp., n = 1, and as A. fumigatus sensu strictu by sequence analysis, n = 1). One live stranded and euthanized animal presented partial hemiplegia of the blowhole and therefore an MRI was conducted, which resulted in a unique image of the extensive, fungus-induced lesion in the left cerebellar hemisphere, deforming and displacing the brainstem, and additionally affected the AS. The gross- and histologic lesions in the 18 porpoises diagnosed with fungal disease were similar to changes described in other mammalian species. The prevalence of fungal disease in free-living harbor porpoises is lower than seen in captive and rehabilitated animals, suggesting that captivity increases the risk to develop mycotic infections. Finally, fungal infection in the CNS and AS are usually considered consequences of vascular dissemination originating from pulmonary foci. However, only 1/7 cases with otitis and/or encephalitis demonstrated pulmonary aspergillosis, suggesting a different pathogenesis.

Within 10 days of ingesting boxelder tree (Acer negundo) cuttings, seven fallow deer (Dama dama) died (n=2) or were euthanased (n=5) after showing signs of colic, anorexia and severe depression. Another fallow deer and two Dutch Landrace goats (Capra aegagrus hircus) simultaneously displayed colic signs but survived. Therapy included intramuscular flunixine meglumine. Postmortem investigation revealed subacute renal tubular necrosis and extensive lung oedema in all animals, and three deer had liver degeneration. The combination of clinical history and postmortem findings lead to the presumptive diagnosis of maple leaf intoxication as described in equids. This is the first report of likely boxelder tree (A negundo) intoxication in animals and the first report of maple leaf intoxication in fallow deer and goats.