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Rapid changes of marine ecosystems resulting from human activities and climate change, and the subsequent reported rise of infectious diseases in marine mammals, highlight the urgency for timely detection of unusual health events negatively affecting populations. Studies reporting pathological findings in the commonly stranded harbor porpoise (Phocoena phocoena) on North Atlantic coastlines are essential to describe new and emerging causes of mortality. However, such studies often cannot be used as long-term health surveillance tools due to analytical limitations. We tested 31 variables gained from stranding-, necropsy-, dietary- and marine debris data from 405 harbor porpoises using applied supervised and unsupervised machine learning techniques to explore and analyze this large dataset. We classified and cross-correlated the variables and characterized the importance of the different variables for accurately predicting cause-of-death categories, to allow trend assessment for good conservation decision. The variable ‘age class’ seemed most influential in determining cause-of-death categories, and it became apparent that juveniles died more often due to acute causes, including bycatch, grey-seal-predation and other trauma, while adults of infectious diseases. Neonates were found in summer, and mostly without prey in their stomach and more often stranded alive. The variables assigned as part of the external examination of carcasses, such as imprints from nets and lesions induced by predators, as well as nutritional condition were most important for predicting cause-of-death categories, with a model prediction accuracy of 75%. Future porpoise monitoring, and in particular the assessment of temporal trends, should predominantly focus on influential variables as determined in this study. Pathogen- and contaminant assessment data was not available for all cases, but would be an important step to further complete the dataset. This could be vital for drawing population-inf

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.

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.

In het broedseizoen van 2022 werden veel wilde vogels in Noordwest Europa getroffen door een zeer besmettelijke, dodelijke variant van het vogelgriepvirus. In negen van de tien Nederlandse kolonies van de grote stern stierven grote aantallen broedvogels (tientallen procenten van alle aanwezige broedvogels) en vervolgens ook de kuikens. In verschillende kolonies, binnen Nederland en in het buitenland, werd hierop verschillend gereageerd door beheerders en onderzoekers, wat achteraf de mogelijkheid gaf om na te gaan hoe het beste om te gaan is met een dergelijke uitbraak. In dit rapport wordt nagegaan, wat de impact is geweest van deze uitbraak en massasterfte en wat het handelingsperspectief is bij volgende uitbraken. Gebleken is, dat het structureel weghalen van dode vogels (broedvogels en kuikens) bij een besmetting in een kolonie, kan helpen om het sterftepercentage te verkleinen. Geadviseerd wordt daarom, om bij iedere volgende uitbraak, zo snel mogelijk te starten met het weghalen van dode vogels uit getroffen kolonies. De infectiegolf kent een aanloopfase van één tot drie weken, waarin er dagelijks nog weinig slachtoffers vallen in de kolonie. Het is zaak om een uitbraak zo vroeg mogelijk te detecteren en daar dan meteen op in te spelen: dit biedt de beste kans om de infectie nog te beteugelen. Voorwaarde voor een snelle en adequate respons is een goede surveillance en een draaiboek, inclusief materiaal om veilig te kunnen werken, dat vooraf beschikbaar is. Andere mogelijkheden om infectiegolven te beteugelen lijken vooralsnog beperkt. Het is aan te raden om kolonies, na een infectiegolf als het broedseizoen voorbij is, te ontdoen van achtergebleven karkassen. Dit om een eventuele persistentie van virus in de bodem, of het doorgeven van het virus aan andere vogels die het gebied in de seizoenen na het broedseizoen gebruiken, zo klein mogelijk te maken. Of, en zo ja hoe lang, het virus in (de omgeving van) dode vogels levensvatbaar aanwezig blijft in kolonies

Humans impact natural systems at an unprecedented rate. The North Sea is one of the regions in the world with the highest levels of anthropogenic activity. Here, the harbor porpoise (Phocoena phocoena) is an abundant species and is often regarded as an ecosystem sentinel. A post-mortem surveillance program was established in the Netherlands aimed at increasing knowledge of the effects of human activities on harbor porpoises. In this study, we describe the pathological findings related to anthropogenic and natural causes of death categories in 612 harbor porpoises that stranded between 2008 and 2019, and assess their relations to age, sex, season, and location. The largest anthropogenic category was bycatch (17%), with mainly juveniles affected and peak periods in March and September–October. Other, infrequently diagnosed anthropogenic causes of death were trauma (4%), largely most likely due to ship collisions, and marine debris ingestion and entanglement (0.3%). The risk of dying from anthropogenic causes was highest for juveniles. Lesions compatible with noise-induced hearing loss were investigated in carcasses which were fresh enough to do so (n = 50), with lesions apparent in two porpoises. Non-direct human-induced threats included infectious diseases, which were by far the largest cause of death category (32%), and affected mainly adults. Also, gray seal (Halichoerus grypus) attacks were a frequently assigned cause of death category (24%). There were more acute predation cases in the earlier study years, while porpoises with lesions that suggested escape from gray seal attacks were diagnosed more recently, which could suggest that porpoises adapted to this threat. Our study contributes to understanding porpoise health in response to persisting, new, emerging, and cumulative threats. Building up such knowledge is crucial for conservation management of this protected species.