Health condition of the Baltic grey seal (Halichoerus grypus) during two decades. Gynaecological health improvement but increased prevalence of colonic ulcers.

Abstract

Results obtained at postmortem examinations of 159 Baltic grey seals during the 20-year period 1977-1996 are presented. The investigation was initiated due to a serious reduction of the Baltic grey and ringed seal populations. Earlier, reduced reproductive ability with occlusions and stenoses of the uterus, as well as a disease complex in adult individuals of both sexes, was reported. The disease complex comprised lesions of claws, skull bone, intestine (colonic ulcers), kidneys (glomerulopathy, tubular cell proliferations), arteries (sclerosis) and adrenals (cortical hyperplasia, cortical adenomas). Besides occlusions and stenoses, tumours (leiomyomas) were common in the uterus. This report focuses on the results of a time-trend study covering the two decades 1977-1986 and 1987-1996. The prevalences (%) in the two decades of moderate to severe lesions of claws, intestine, arteries and adrenals are compared, as well as the prevalences of lesions of the female reproductive organs and rate of pregnancy. A similar comparison was made of animals born before 1980 and those born after 1979, in order to investigate a possible relation between the evident decrease in PCB and DDT pollution of the Baltic which occurred in the 1970s and seal health. A positive time trend respecting gynaecological health was confirmed, with a decreased prevalence of uterine obstructions, from 42 to 11%, and an increased prevalence of pregnancies, from 9 to 60%. The high incidence of uterine tumours (leiomyomas) seems to have decreased slowly (from 53 to 43%). Of special interest is the increased prevalence of colonic ulcers in young animals. The findings indicate that the food consumed by the Baltic seals may contain "new" or increased amounts of hitherto unidentified toxic factors which affect their immune system.