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This annual report presents the results of post-mortem examinations of stranded harbour porpoises in 2020. One of the main objectives of the research is to quantify human-induced causes of death. In 2020, 49 dead harbour porpoises were examined: 27 males and 22 females, 28 adults, 9 juveniles and 12 neonates. In addition 3 foetuses were found. Most of the examined harbour porpoises died as a result of infectious diseases (37%) and grey seal attacks (20.4%). Trauma of other origin was the most likely cause of death for 6 porpoises (12.2%) and bycatch for one porpoise (2%). In dit jaarrapport worden de resultaten gepresenteerd van pathologisch onderzoek aan gestrande bruinvissen in 2020. Een van de hoofddoelen van het onderzoek is het kwantificeren van sterfte van bruinvissen door menselijk toedoen. In 2020 zijn 49 dode bruinvissen onderzocht: 27 mannelijke en 22 vrouwelijke, 28 volwassen, 9 juveniel en 12 neonaat. Er werden daarnaast 3 foetussen gevonden. De meeste van de onderzochte bruinvissen waren gestorven door infectieziekten (37%) en grijze zeehondaanvallen (20,4%). Trauma van andere oorsprong was de meest waarschijnlijke doodsoorzaak van 6 bruinvissen (12,2%) en bijvangst van één bruinvis (2%).

The death and behaviour prior to death of a bottlenose dolphin (Tursiops truncatus) known by the name of “Zafar” created significant national and international public interest. The animal was first observed in the Netherlands on the 2nd of May 2020, closely following a boat from Brittany, France, all the way into the port of Amsterdam after passing the locks at IJmuiden. After a day of residency in the industrial port of Amsterdam, the animal was successfully lured back into the North Sea. The dolphin was observed lastly on the 5th of May following a fishing vessel heading north in coastal waters near Callantsoog. Seven days later, a dead bottlenose dolphin stranded at Wijk aan Zee and through photo-identification, the animal was identified to be Zafar. A post-mortem investigation was carried out with the aim of determining the animal’s most likely cause of death, its health status, and an attempt was made to unravel the animals approximate whereabouts prior to death through stomach content analysis. The post-mortem investigation revealed that this subadult, 14 year old male had a moderate to good body condition, no sign of significant disease, and had been feeding shortly prior to death. Injuries on the animal fit with an anthropogenic source causing mortality, and the nature and severity of the lesions were most consistent with vessel collision. Based on the sightings and stranding location and the stomach content, the animal probably died within the Dutch coastal waters of Noord-Holland. This animal was first sighted in 2017 as a solitary-sociable dolphin. Such individuals have particular home-ranges, typically interact with people and little with conspecifics. It has been reported that solitary-sociable dolphins have a higher chance of suffering from human interference, and the case of Zafar clearly demonstrates this risk.