Orca (Orcinus orca) strandings are rare and post-mortem examinations on fresh individuals are scarce. Thus, little is known about their parasitological fauna, prevalence of infections, associated pathology and the impact on their health. During post-mortem examinations of two male neonatal orcas stranded in Germany and Norway, lungworm infections were found within the bronchi of both individuals. The nematodes were identified as Halocercus sp. (Pseudaliidae), which have been described in the respiratory tract of multiple odontocete species, but not yet in orcas. The life cycle and transmission pathways of some pseudaliid nematodes are incompletely understood. Lungworm infections in neonatal cetaceans are an unusual finding and thus seem to be an indicator for direct mother-to-calf transmission (transplacental or transmammary) of Halocercus sp. nematodes in orcas.
Cortisol is known to reflect the level of the stress response. However, measuring the cortisol concentration only once fails to provide sufficient information about the duration of the stress exposure. Moreover, handling is an acute stressor and increases cortisol secretion especially in wildlife species. Yet, in phocids reliable indicators are missing that reflect potential chronic effects of stress. The adrenal-derived steroid hormone dehydroepiandrosterone (DHEA) has been described as biomarker for the assessment of the stress status but has not been applied to marine mammal stress research. Therefore, DHEA, the sulfated precursor DHEAS and the cortisol/DHEA ratio were determined in serum of different seals. One group consisted of harbor ( Phoca vitulina) and gray seals ( Halichoerus grypus) that were habituated to human handling. The other two groups included healthy and free-ranging seals suffering from a disease. Blood samples were taken from 11 habituated (six males, five females), 17 wild_healthy (13 males, four females), and nine wild_diseased seals (four males, five females). No differences in serum cortisol levels could be detected between wild_healthy and wild_diseased seals. On the contrary, wild_diseased seals showed the lowest DHEA concentration compared to the other two groups. Wild_diseased seals also revealed the highest cortisol/DHEA ratio compared to the habituated_zoo (2,074.7 ± 351.4 vs. 121.5 ± 26.8, P < 0.001) and wild_healthy seals (827.9 ± 214.3, P < 0.01). DHEA and the cortisol/DHEA ratio may reflect differences in the functionality of the hypothalamic-pituitary-adrenal axis and therefore represent valuable tools for the assessment of stress-related effects in seals.
Intestinal displacements including volvulus, torsion and invagination have been reported in various terrestrial and marine mammals. We conducted pathological investigations on 157 seals that had either stranded on the coasts of the North or Baltic Sea between 1996 and 2015 (115 harbour seals, >19 mo old; 21 grey seals, >13 mo old) or died while in human care (18 harbour seals, >19 mo old; 3 grey seals, >13 mo old). Intestinal displacements were found in 23% of the examined free-living harbour seals, in 5% of the stranded grey seals and in 17% of the harbour seals in human care. Intestinal volvulus, found in 24 cases, was characterized by twisting of the intestine along the mesenteric axis (180-540°) resulting in vascular obstruction and haemorrhagic infarction. In harbour seals, the sex ratio of individuals suffering from volvulus tended to be biased towards females during April to June, suggesting an elevated risk for pregnant females around birth time. Invagination was detected in 11 cases, 5 of which suffered from additional volvulus. Pathological findings associated with intestinal volvulus and invagination were sero-haemorrhagic effusions in the abdominal cavity. Enteritis, parasitic infection with gastric nematodes and intestinal acanthocephalans and bacterial infection with predominantly Clostridium perfringens and Escherichia coli were observed in most of the affected animals. In total, 30 investigated harbour and grey seals suffered from intestinal displacements. Pregnant females seemed to be more vulnerable around birth time. Causes of intestinal displacements remain undetermined, but are likely multifactorial.
In order to conduct an objective evaluation of potential ecological effects of grey seal predation on marine mammals, it is essential to establish a broad knowledge base helping in the thorough identification of such cases during post-mortem examination. The aim of this work is to report and discuss outcomes resulting from a retrospective evaluation of harbour (Phoca vitulina) and grey seal (Halichoerus grypus) stranding and necropsy data (n = 3274). In addition, the results are compared to a recent case of definite grey seal predation from Germany as well as reports from other countries. Carcasses potentially subjected to grey seal predation show severe lacerations with a circular pattern leaving a smooth, linear and cut-like wound margin. Large parts of skin and underlying tissue are detached from the body and loss of blubber is common. Occurrence frequencies of encountered lesions are presented and a list of parameters to be used for the assessment of similar cases as well as a complementary decision tree are suggested. With the proposed parameters, categories and tools, a baseline can be built in order to facilitate the standardised recognition of predation cases during post-mortem examinations of seals between groups working with populations across several geographic ranges.
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