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We monitor the demographic structure and health (reproduction, body condition and the occurrence of parasites) of the Baltic seals in Finland. Goals We collect samples of grey and ringed seals from hunters and fishermen: the lower jaw, reproductive organs and liver. Hunters/fishermen also measure the head-body length and the thickness of the blubber layer of the seals, and, if possible, weigh the seals. We wish to get samples both from hunted and by-caught seals.
Age determination is done from the sections of lower canine teeth. We examine uteri for embryos, fetuses or placental scars. We also check uteri for occlusions. We examine the occurrence of corpus luteum and corpus albicans in ovaries. The reproductive potential of females is determined from the information obtained from uteri and ovaries: ovulation rate, pregnancy rate and birth rate. Body condition is determined from the thickness of the blubber layer. Pregnancy rate/birth rate and blubber thickness are used (e.g. by Helcom) as health indicators of seals when monitoring the environmental status of the Baltic Sea. Livers are examined for the liver fluke in the Finnish Food Safety Authority Evira.
Results Seal samples have been collected since 2000. Most samples are from grey seals, in recent years we have received 100-150 grey seal samples/year, altogether about 1800 samples. The demographic structure of the grey seal population has changed during the 2000s: the mortality rate of females <10 years of age has increased, which may affect the population growth rate. The proportion of females (especially those in the best reproductive age) has decreased in the population. Because also the birth rate has decreased, the population now produces fewer pups than in the early 2000s.
The demographic structure of the grey seal catch differs between the sea areas: in the Gulf of Bothnia hunting mainly takes place on the ice in late spring and the majority of the catch is females (except pups), while in the Archipelago Sea hunting more often takes place in autumn and the majority of the catch is males. Human induced mortality, i.e. hunting and by-catch mortality may be a significant mortality factor of grey seals.
Impact of research On the basis of the results of this project we can estimate the status of the grey seal population in the Finnish sea area (demographic structure, reproductive potential, mortality rate, nutritional status, parasite load) and further, the environmental status of the Baltic Sea (HELCOM CORESET indicators) as well as human impact (e.g. hunting and fisheries) on seal populations. Researcher in charge Kauhala Kaarina, Finnish Game and Fisheries Research Institute
Contacts
Project Partners Finnish Food Safety Authority Evira, hunters, fishermen, Finnish Wildlife Agency, Swedish Museum of Natural History Project phase: Completed
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