Reproductive status of the female Baltic ringed seal
The population of ringed seals in the Baltic Sea was estimated to around 190 000–220 000 individuals in the 1900’s and decreased to approximate 5 000 in the late 1970s. The number of pregnant females also decreased during this time. This decreased pregnancy rate has been explained to be due to hunti...
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| Format: | Other/Unknown Material |
| Language: | English Swedish |
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SLU/Dept. of Clinical Sciences
2019
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| Online Access: | https://stud.epsilon.slu.se/14878/ |
| Summary: | The population of ringed seals in the Baltic Sea was estimated to around 190 000–220 000 individuals in the 1900’s and decreased to approximate 5 000 in the late 1970s. The number of pregnant females also decreased during this time. This decreased pregnancy rate has been explained to be due to hunting and environmental pollutants such as dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyl (PCB) leading to pathological lesions (occlusions) in the uterus blocking the passage from the uterine horn to the ovary. Around 1970, the environmental pollutants were restricted in Sweden and in the 1990s the ringed seal population started to increase. Today the annual growth rate of the ringed seal population is estimated to be 5%. This is still considered to be a slow growth rate compared to other seal populations which can have a growth rate of around 10%. This master thesis includes a study of the reproductive status of 142 female Baltic ringed seals necropsied by personnel at the Swedish Museum of Natural History from 2002–2018. Reproductive parameters were recorded such as lesions, ovary weight, pregnancy and corpus luteum and corpus albicans size. Specific measurements in ringed seal female reproductive organs, such as length and width, and blastocyst flushing were also performed. Data was grouped based on time of death: spring or fall. Specific measurements of the size and weight of the female reproductive organs were described which has not been done before. This master thesis found that occlusions were observed in three females (6.8%) in the last 16 years. This could potentially be at least partially explained by bacterial infections causing abortions which in turn lead to occlusions and sterility. However, tissue concentrations of PCB in the affected females were not analyzed. Future studies including the male ringed seals part in the reproductive status of the species has been found to be needed. Vikarepopulationen i Östersjön var under tidigt 1900-tal uppskattad till 190 000–220 000 individer. ... |
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