Pathological findings in stranded harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) in the Netherlands between 2009 and 2014.

Abstract

In this study necropsy has been performed on 206 wild seals from the Wadden Sea, of which 158 harbour seals (Phoca vitulina), 22 grey seals (Halichoerus grypus) and 26 of which the species could not be determined, to determine what caused the animals to strand. The seals stranded on the Dutch coastlines between 2009 and 2014. They were further divided depending on the fact if the animal was found dead or died soon after stranding or if the animal was euthanized. The presence of morphologic abnormalities were the highest in the alimentary tract (203 abnormalities were scored in this category. In most cases the cause of death remained unknown after necropsy (50,5%). The hypothesis of the study was, that there were no differences in causes of death between the species, between the animals that were found dead or that were euthanized and that there were no differences between this studies results when comparing the to earlier studies. The cause of death that was established the most in the seals that were examined, was parasitic bronchopneumonia (13,5%), followed by septicaemia (12,6%). The grey seals significantly died more often due to emaciation (P=0.023) or inferred bycatch (P=0.040), in comparison with the harbour seals. Euthanized harbour seals, in comparison with harbour seals that were found dead or died soon after stranding (<24 hours), significantly died more often due to parasitic bronchopneumonia (P=0.004) and significantly more often the cause of death could be determined in this group (P=0.012). In a previous study that examined seals between 1996 and 2005(1), significantly more harbour seals died from parasitic bronchopneumonia (P=0.007), perinatal death (P=0.000) and ecto- and endoparasitism (P=0.012). The other way around, more harbour seals along the Dutch coastline died due to flipper abscesses (P=0.029), pup starvation (P=0.009), foreign bodies (P=0.001) and causes Comparing the findings in seals in the Wadden Sea with earlier periods, significantly more harbour seals died due to pup starvation (P=0.012) and inferred bycatch (P=0.000) between 1979 and 2008. On the other hand, between 2009 and 2014 significantly more harbour seals died due to parasitic bronchopneumonia (P=0.000), septicaemia (P=0.000), emaciation of unknown origin (P=0.000) and physical trauma (P=0.026).