Pathological changes in seals in Swedish waters: the relation to environmental pollution

• Main Author: Bergman, Anders
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2007
• Subjects: harbour seal; Phoca hispida; Phoca vitulina; ringed seal
• Online Access: https://pub.epsilon.slu.se/1681/; https://pub.epsilon.slu.se/1681/1/AB-avhandling-epsilon.pdf

This thesis concerns the disease situation for the three seal species that inhabit the Swedish coastal waters; the grey seal (Halichoerus grypus), the ringed seal (Phoca hispida botnica) and the harbour seal (Phoca vitulina). A severe decline of the populations of Baltic grey and ringed seals took place during the second half of the 1960s. It was suggested to be caused by the contamination by industrial chemicals, above all organochlorines such as PCB and DDT. High concentrations of these substances were found in the Baltic biota. The author has performed necropsy or examination of organ samples from animals, which were found dead on shore, by caught at fishery or killed by hunting during 1977-2002. Multiple chronic organ lesions were found most prominent in the female reproductive organs (uterine stenoses and occlusions), intestines (colonic ulcers) and adrenals (cortical hyperplasia). Severe lesions were present also in the skeleton, integument and kidneys. The character and distribution of the lesions was regular and the disease picture tentatively was named the Baltic Seal Disease Complex (BSDC). The changes in the female reproductive organs indicate that reproductive failure is an important factor behind the decline of the Baltic seal populations. Adrenocortical hyperplasia was a regular and striking component of the BSDC. It is a common feature of prolonged stress in animals and man. The animals in this study have suffered from severe inflammatory processes in connection with more or less advanced malnutrition due to hampered ingestion and digestion of food. This is in the author’s opinion the most probable explanation of the adrenal changes. Inflammatory changes were most prominent in the intestines with deep ulcerations, in several cases leading to perforation of the intestinal wall. Bacteriological investigation revealed opportunistic or pathogenic micro-organisms but a common bacterial aetiology could not be suggested. The severity and wide dispersion of the lesions are interpreted as signs of a ...