Causes of death of harbor porpoises (Phocoena phocoena) stranded on the coasts of Belgium and Northern France

Abstract

The multidisciplinary research group MARIN (Marine Animals Research & Intervention Network) investigated the causes of death of marine mammals stranded on the continental coastline of the southern North Sea (Belgium and France). Since the end of the 1990s, a significant rise of harbour porpoise (Phocoena phocoena) strandings occurred in the southern North Sea, the annual stranding average being 7 porpoises between 1990 and 2000, and 57 between 2001 and 2008. The aim of the present study is to present the main lesions and causes of death of porpoises stranded on the continental coastline of the southern North Sea and their evolution between 1990 and 2008 During the period, 520 porpoises found dead were necropsied and sampled following a standard procedure (Jauniaux et al, 2002). Frequent observations included fishing net abrasions on the skin and sub-cutaneous, muscular bruises, emaciation, pulmonary and gastric parasitism, acute pneumonia, pulmonary congestion and edema. Two mains causes of death emerged: capture in fishing nets (by-catch) and infectious diseases. The first one was mainly observed in March and April while infectious diseases, mainly acute pneumonia associated with parasites infestation, occurred evenly throughout the year. Only 47% of by-caught animals were in good condition, others having evidence of slight to severe emaciation, acute pneumonia and mild to severe parasitosis. One of the main reason for the recent porpoises stranding rise on the continental coastline of the southern North Sea is linked with the southward shift of the population within the North Sea.