Analysis of stranding data and pathological findings in stranded harbor seals and grey seals on Texel and the North-West coast of the Netherlands between 2009 and 2012.

Abstract

Stranding data and pathological findings were analyzed for harbor seals and grey seals that stranded on Texel and the North-West coast of the Netherlands between 2009 and 2012. Stranding data were analyzed for 170 stranded seals (137 harbor seals, 16 grey seals, 17 unknown) and consisted of the date of stranding, stranding location, age category, sex and species. Pathological findings were evaluated for 40 seals (38 harbor seals and 2 grey seals) that died or were euthanized due to severe illness in rehabilitation centre Ecomare during the winter of 2011 to 2012. Weight, sex, lengths, decomposition condition code, nutritive condition code and macroscopical observations of organs and lesions were analyzed. Samples of organs were collected for histological, virological (morbillivirus, phocine herpesvirus, influenzavirus), bacteriological and parasitological examination. Stranded seals were mainly in the age category of juvenile. Strandings were most frequent in June and July (neonate harbor seals) which corresponds with the pupping season of this species. The highest stranding rate was during the winter months (December and January), which indicates that juveniles in particular may have difficulties with surviving winter due to bad weather conditions and a not completely developed immune system. Most frequently found observations in rehabilitation seals were a poor nutritive condition (52,5%), skin ulceration (28,9%), subcutaneous hemorrhage (18,4%), lungworm infection (70%), interstitial edema (62,5%) and hyperemia (47,5%) (acute pneumonia), lung atelectasis (26,3%), multifocal necrosis in the liver (10,5%) and parasite infections of the gastro-intestinal tract (72,5%). Acute pneumonia was in most cases associated with the presence of lungworms (Otostrongylus circumlitus and Parafilaroides gymnurus). Bacterial infections were suggested to be secondary to verminous pneumonia. Poor nutritive condition in stranded seals was probably due to disease and a lack of feeding because of separation from the mother. Lungworm infections were in most cases mild, but because of the frequent findings of acute pneumonia and the relatively high number of unexpected deaths of seals after an apparently successful completed treatment, it is suggested that that the provided treatment in rehabilitation was not sufficiently effective in overcoming the lungworm infestation and associated inflammation.