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Odevall, Alexandra, 2019. Reproductive status of the female Baltic ringed seal. Second cycle, A2E. Uppsala: SLU, Dept. of Clinical Sciences

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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. Denna siffra sjönk till ca 5 000 individer under sent 1970-tal. Även antalet dräktiga honor minskade under denna period vilket förklarats av jakt och miljögifter så som dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyl (PCB). PCB och DDT ska ha medfört patologiska lesioner (ocklusioner) i uterus som lett till att passagen mellan uterushorn och äggstock blockerats. Dessa miljögifter förbjöds i Sverige runt 1970 och på 1990- talet sågs en populationsökning. Idag uppskattas den årliga tillväxthastigheten hos vikare i Östersjön att vara ca 5 % vilket anses lågt jämfört med andra sälpopulationer som ligger runt ca 10 %.

Detta examensarbete har undersökt reproduktionsstatus hos 142 vikarehonor från Östersjön som obducerats av personal på Naturhistoriska Riksmuseet mellan 2002–2018. Parametrar såsom lesioner, ovarievikt, dräktighet, och storlek på corpus luteum och corpus albicans noterades. Specifika mätningar hos vikarehonors reproduktionsorgan, så som längd och bredd, och blastocystsköljning utfördes också. Datan delades sedan in i vår eller höst beroende på när vikaren dog.

Specifika mätningar av storleken och vikten av det honliga reproduktionsorganet har beskrivits, något som inte gjorts tidigare. Detta examensarbete fann att 3 (6,8 %) fall av ocklusioner har observerats under de senaste 16 åren. Detta kan åtminstone delvis förklaras av bakterieinfektioner som gett upphov till abort som i sin tur gett ocklusioner och sterilitet. PCB koncentrationer hos dessa individer har dock ej undersökts och framtida studier inom området behövs.

Main title:Reproductive status of the female Baltic ringed seal
Authors:Odevall, Alexandra
Supervisor:Persson, Sara
Examiner:Dalin, Anne-Marie
Volume/Sequential designation:UNSPECIFIED
Year of Publication:2019
Level and depth descriptor:Second cycle, A2E
Student's programme affiliation:VY002 Veterinary Medicine Programme 330 HEC
Supervising department:(VH) > Dept. of Clinical Sciences
Keywords:Baltic ringed seal, occlusion, PCB, DDT, reproduction
Permanent URL:
Subjects:Animal physiology - Reproduction
Deposited On:03 Oct 2019 10:50
Metadata Last Modified:04 Jun 2020 13:55

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