Saimaa Ringed Seal Research Articles

Home range, survival, and dispersal of endangered Saimaa ringed seal pups: Implications for conservation

AbstractLake Saimaa in eastern Finland is inhabited by a critically endangered ringed seal subspecies Pusa hispida saimensis. Since accidental mortality in gill nets, resulting in reduced pup survival, is considered to be the main factor contributing to the decline in its population, fishing restriction areas have been established. In this study, 10 pups were located daily using very high frequency (VHF) telemetry to estimate their home ranges, movements, and survival. The pups dispersed after weaning at the age of ca. 3 mo and moved up to 15 km a day between consecutive locations and up to 25 km away from their birth sites. The home ranges of the pups at the age of 3–4 mo were variable in size, from 3 to 162 km2. The pups preferred the same shallow water areas (<6 m) that were used for gill net fishing. The annual fishing restrictions covered an average of 83% of the pups’ home ranges. Four of the pups were nevertheless killed in fishing gear. The results have implications for Saimaa ringed seal management and conservation. For instance, large home ranges of pups and the long distances movements should be taken into account when zoning shore use and imposing fishing restrictions.

Vertical fatty acid profiles in blubber of a freshwater ringed seal — Comparison to a marine relative

We investigated the vertical stratification pattern of fatty acids in the blubber of the freshwater Saimaa ringed seal (Phoca hispida saimensis; n=35). Blubber was dissected vertically into 3mm thick sequential subsamples, and the fatty acid composition was analyzed separately for each subsample. The combined vertical fatty acid profiles (expressed as numerical gradients) showed that the blubber of >1year old individuals is stratified into three distinguishable layers: superficial (~1.5cm), middle and deep (~1cm). Thickness of the middle layer varied according to the total blubber thickness. We suggest that the observed layering is related to the differences in the tissue temperatures and metabolic activity in the blubber column. The dissimilarity in the fatty acid composition (measured as Euclidean distance) between the different blubber layers and the 5 most important fish prey species available in Lake Saimaa was largest in the superficial blubber. In fact, the fatty acid composition of superficial blubber resembled more that of marine ringed seal (Phoca hispida hispida) blubber than any of the analyzed fish species. The composition closest to that of the prey was found in the deep blubber of the Saimaa ringed seal. The large vertical differences in the fatty acid composition of blubber lipids, which likely affect the vertical distribution of other endogenous or exogenous lipophilic substances as well, will set conditions for the sampling of blubber for biomonitoring and dietary studies. Thus the knowledge on the potential layers with different composition and the depths they span in different individuals (e.g. young versus old; with thin versus thick blubber) is crucial for improving the validity and reliability of monitoring methods utilizing the blubber tissue.

Vocal repertoire of the Saimaa ringed seal (Phoca hispida saimensis) during the breeding season

Marine Mammal ScienceVolume 25, Issue 4 p. 920-930 Vocal repertoire of the Saimaa ringed seal (Phoca hispida saimensis) during the breeding season Anni Rautio, Anni Rautio Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandE-mail: anni.rautio@joensuu.fiSearch for more papers by this authorMarja Niemi, Marja Niemi Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandE-mail: anni.rautio@joensuu.fiSearch for more papers by this authorMervi Kunnasranta, Mervi Kunnasranta Finnish Game and Fisheries Research Institute, Turku Game and Fisheries Research, Itäinen Pitkäkatu 3A, FI-20520 Turku, FinlandSearch for more papers by this authorIsmo J. Holopainen, Ismo J. Holopainen Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandSearch for more papers by this authorHeikki Hyvärinen, Heikki Hyvärinen Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandSearch for more papers by this author Anni Rautio, Anni Rautio Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandE-mail: anni.rautio@joensuu.fiSearch for more papers by this authorMarja Niemi, Marja Niemi Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandE-mail: anni.rautio@joensuu.fiSearch for more papers by this authorMervi Kunnasranta, Mervi Kunnasranta Finnish Game and Fisheries Research Institute, Turku Game and Fisheries Research, Itäinen Pitkäkatu 3A, FI-20520 Turku, FinlandSearch for more papers by this authorIsmo J. Holopainen, Ismo J. Holopainen Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandSearch for more papers by this authorHeikki Hyvärinen, Heikki Hyvärinen Faculty of Biosciences, University of Joensuu, P. O. Box 111, FI-80101 Joensuu, FinlandSearch for more papers by this author First published: 22 October 2009 https://doi.org/10.1111/j.1748-7692.2009.00299.xCitations: 13Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume25, Issue4October 2009Pages 920-930 RelatedInformation

Person, Place, and Knowledge in the Conservation of the Saimaa Ringed Seal

There is a strong connection between people's knowledge of nature and their relationship to place. Local environmental knowledge is multifaceted and influenced by changing social and economic circumstances that affect the way people come to know and relate to nature. A case study from Finland demonstrates how locality, personhood, and environmental perceptions cohere to challenge conservation practices. In this instance, local people fully uphold the conservationists' desire to save a threatened endemic mammal, the Saimaa ringed seal (Phoca hispida saimensis nordq), from extinction. However, local people are far less enthusiastic about the conservationists' chosen means for achieving conservation of the seal. They fail to engage with many aspects of the conservation program because its design and implementation fail to acknowledge local people's collective and personal experiences of place. The case study demonstrates the need for conservation programs to take seriously local people's “place-based” observations and theories.

Comparative use of vendace by humans and Saimaa ringed seal in Lake Pihlajavesi, Finland

The Saimaa ringed seal, Phoca hispida saimensis, is one of the most endangered ringed seals in the world. Its total population consisted of 240 adult seals in the Saimaa lake complex in 2000. We estimated the amount of vendace, Coregonus albula, consumed by the seals and compared it with fishermen’s vendace catches and our vendace stock estimates in Lake Pihlajavesi, Finland. Our study area was the habitat of 43 mature seals and 17 immature seals as well as 12 pups in 2001. Five commercial two-boat trawlers fished in the area. Vendace stock size was estimated at 660 tonnes i.e., 12 kg ha −1 in the study area in August–September 2001. The vendace catch by fishermen was approximately 250 tonnes, and the vendace consumption by the Saimaa ringed seal was estimated at 68 tonnes in 2001. We estimated that during the whole year seals ate approximately 8% of the vendace spawning stock biomass in the area while fishermen caught 30% of it. The seals and the fishermen together used less than 10% of the available vendace biomass in each month. Fishing pressure on the vendace stock was highest in August–October. The amount of vendace eaten by the seals exceeded the vendace catch in fisheries only in December–April. In periods of low vendace density, the seals can consume a higher proportion of the stock and reduce the catch per unit of effort in fisheries. However, our assumption that seals fed only on vendace should be considered as an extreme scenario when considering the conflict between fisheries and the seal.

Attitudes towards fishery and conservation of the Saimaa ringed seal in Lake Pihlajavesi, Finland

The Saimaa ringed seal (Phoca hispida saimensis) is the only endemic mammal in Finland. At present the total population size of this subspecies is c. 250 individuals. Because the seal feeds on fish, and because of its value particularly as a source of meat, oil and leather, hunting was allowed until 1955. Conservation of the seal and some of its lairing areas by means of fishing restrictions requires the adoption of new attitudes. Semi-structured interviews elucidated the basis of conflicts concerning protection of the Saimaa ringed seal and fishing in Lake Pihlajavesi, Finland, where one of the most viable populations of the seal lives. Socio-economic position largely determined personal attitudes towards conservation; local landowners felt that their use of natural resources was restricted, while summer cottage owners wanted strict conservation. Commercial fishers considered the protection of the ringed seal unnecessary and a waste of money. Conservation biologists believed that the proposed actions were necessary to reduce the risk of extinction. Attitudes were also widely influenced by culture and social backgrounds. Those influenced by the traditional Finnish peasant/nature relationship had a different vision of nature from the conservationists who were influenced by modern science. Questions raised by the protection of the Saimaa ringed seal form an example of transition of an environmental conflict to larger-scale criticism of ongoing structural transformation in society. It is obvious that if nature conservation requires the approval of all social groups, it needs a change of authoritarian measures and acceptance of local knowledge, which should be used alongside scientific knowledge in management. Nature conservation policy led by specialists and authorities could be seen as widening the gap between urban and rural areas.

Institutional changes in fisheries governance: the case of the saimaa ringed seal, Phoca hispida saimensis, conservation

AbstractInstitutional and paradigmatic changes in Finnish fisheries and environmental governance in the light of the protection of the Saimaa ringed seal, Phoca hispida saimensis Nordq., are discussed. The analysis is based on written statements by stakeholder institutions in response to a proposal by the Ministry of Agriculture and Forestry to restrict fishing in the breeding areas of the ringed seal. The controversy about the conservation of the Saimaa ringed seal is a revealing example of transition of an environmental conflict into a larger scale criticism of ongoing transformations in society related to paradigmatic changes of fisheries governance institutions. In addition to changed emphasis in different basic world outlooks, the contexts of the paradigms have changed. The policy restricting fishing by the authorities to support seal conservation is located between the paradigms of conservation and rationalisation. The Government has aligned itself with modern conservation ideas, but at the same time aroused strong resistance from the local level of fisheries governance. The local and regional stakeholders emphasised private water ownership, local knowledge and already established local agreements for seal conservation.

The impact of sexual selection on Corynosoma magdaleni (Acanthocephala) infrapopulations in Saimaa ringed seals (Phoca hispida saimensis).

In free-living animals sexual selection is a central force shaping the spatial distribution of individuals in a population as well as sexual size dimorphism. We studied the influence of sexual selection on spatial distribution, female-to-male body size ratio, and female mating success of acanthocephalans in a natural host population of Saimaa ringed seal (Phoca hispida saimensis) harbouring a single intestinal helminth species, Corynosoma magdaleni. The acanthocephalans were always found along the full length of the small intestine; however, the site selection varied among the individual seals according to the age of the infection. The distribution of male acanthocephalans was not random with respect to females, with larger males tending to aggregate around non-mated females. A higher proportion of C. magdaleni females had copulated in seals with relatively more male worms. Male-male competition for access to females can be intense in C. magdaleni infrapopulation and may select for large males. We found that the larger the infrapopulation size, the smaller the males compared to females. In addition, the greater the female bias in the infrapopulation, the smaller the testes of males. Our study shows that sexual selection may be an important determinant of spatial distribution, male body size and female mating success of C. magdaleni in Saimaa ringed seal.

Intestinal helminths of a landlocked ringed seal (Phoca hispida saimensis) population in eastern Finland.

A small, landlocked, endangered ringed seal (Phoca hispida saimensis) population lives as a postglacial relict in Lake Saimaa in eastern Finland. In this study, the intestinal metazoans were examined from a total of 61 Saimaa seals found dead from 1981 to 2001. The helminth fauna was very depauperate. Only one acanthocephalan species, Corynosoma magdaleni, has been able to survive during isolation in the freshwater environment. In addition, only two cestode species were found: Diphyllobothrium ditretum and Schistocephalus sp. However, neither of these larvae developed in the ringed seals. As the newborn pups of Saimaa seals are nursed for about 2 months only one of them was infected by C. magdaleni. At 2-5 months the pups harboured worms; however, the mean intensity did not rise distinctively until the seals were adults. C. magdaleni infection increased with increasing age and the abundances were significantly different between the age groups. There was no correlation between the number of parasites and the adult seal body weight; however, seals weighing 36 kg or more carried the majority of the worms. The distribution of the parasites was aggregated; six seals carried 65% (n=1,182) of all worms (total n=1,809) and 26 seals were uninfected. Variation in the number of worms in individual seals may indicate differences in feeding behaviour and in the diet of seals, and/or variation in the immune status of the seals.

Postglacial loss of microsatellite variation in the landlocked Lake Saimaa ringed seal

The Lake Saimaa ringed sealPhoca hispida saimensis has lived as anisolated landlocked population in easternFinland since the early post-glacial. In thelast century, the population crashed down to c.200 individuals, and is under a constant threatof extinction. We evaluated the genetic historyof the Saimaa population through a comparisonwith the conspecific sister populations in theArctic Ocean and the Baltic Sea, which haveretained high levels of variation since thedeglaciation. At eight microsatellite loci, thecurrent gene diversity (heterozygosity) of theSaimaa seal was 69% lower than in thereference populations. Allowing reasonablemutation rates (μ = 10−4), thisimplies a long-term post-glacial effectivepopulation size of Ne ≃ 350,and a slow average rate of inbreeding ΔF≃ 0.15% per generation during the c.860 generations (9 500 years) of isolation. Thecurrent Ne is an order of magnitudesmaller and ΔF correspondinglylarger. Whereas the additional loss of markervariation in the short term will not be highrelative to that already taken place, it seemsunwarranted to suppose that the past, slowinbreeding would have effectively purged thepopulation of genetic load and reduced thegenetic risks from small population size.Although the population is now clearlygeographically subdivided in the complex lakesystem, we found little genetic differentiationbetween main breeding areas (FST =0.02). However, at the current low populationdensities, the subdivision may markedly furtherincrease the future rate of inbreeding.

Organochlorine concentrations in the saimaa ringed seal (Phoca hispida saimensis) from Lake Haukivesi, Finland, 1981 to 2000, and in its diet today

Organochlorine and mercury (Hg) pollution has been one possible reason for a decline in the size of the population of the Saimaa ringed seal (Phoca hispida saimensis) in Lake Haukivesi, Finland. In this study, we analyzed changes in the concentrations of organochlorine compounds (OCls) and extractable organic halogen (EOX) in the blubber of Saimaa ringed seals that died from 1981 to 2000. In addition, the present concentrations and biomagnification factors of OCls and Hg from the main prey fish of ringed seal and pike (Esox lucius) were determined. Concentrations of pollutants in bream (Abramis brama) also were analyzed. The decline in the OCl concentrations in blubber was, on average, 25% during the two decades since polychlorinated biphenyls and DDT compounds were banned. Today, concentrations in blubber of Saimaa ringed seals are similar of those in ringed seals from the Arctic. Correspondingly in fish, the OCl and Hg concentrations were, on average, similar to those found in other studies on Finnish and Arctic areas. The low diet concentrations and metabolism of OCls also reflect the lower age correlation of OCls in the male ringed seals in the 1990s than in the 1980s. Biomagnification was considerably higher from fish to the ringed seal than from prey fish to pike because of higher feeding rate of ringed seals and differences in the metabolisms of these animals.

Dive types and circadian behaviour patterns of Saimaa ringed sealsPhoca hispida saimensis during the open-water season

Diving and circadian behaviour patterns of 7 free-ranging Saimaa ringed sealsPhoca hispida saimensis Nordquist, 1899 were examined by VHF-radiotelemetry during open-water seasons between May and November in Lake Saimaa, eastern Finland. The mean recorded dive duration ranged from 2.8 to 6.5 min, with a maximum of 21 min. The mean dive depth ranged from 9.8 to 15.7 m, with maximum of 39.6 m. The maximum dive depth of each seal was limited by water depth in the study area. The dive depths were positively correlated with dive duration and body mass of the seal. Five different dive types were defined, as based on their depth-time characteristics, each falling into one of the three functional categories: travelling, feeding, and resting. Long duration diving bouts occurred mostly at night and were presumed to be resting dives. Saimaa ringed seals exhibited a circadian pattern of haul-out behaviour that shifted seasonally. During molting (May–June) the seals hauled-out both day and night, but later in summer haul-out was more frequent at night.

Analysis of organochlorine compounds and extractable organic halogen in three subspecies of ringed seal from Northeast Europe

AbstractOganochlorine compounds in blubber samples of the ringed seal (Phoca hispida saimensis, P. h. ladogensis, and P. h. hispida) were analyzed in order to estimate the state of pollution in three different water areas in Northeast Europe, namely, Lake Saimaa in Finland, Lake Ladoga, and the White Sea in Russia. Geographic differences in concentrations and in relative concentrations of tri‐ and tetrachlorocymenes, hexachlorobenzene, α‐HCH, β‐HCH, ‐γ‐HCH (Lindane), seven polychlorinated bi‐phenyl (PCB) congeners, and p,p′‐DDT and its metabolites in ringed seals were compared. Concentrations of chlorinated hydrocarbons varied between the water areas. The highest concentrations were found in Saimaa ringed seals, followed by Ladoga ringed seals, and the lowest concentrations were detected in ringed seals from the White Sea. Extractable organic halogen (EOX) concentrations in blubber were also analyzed. The concentrations showed a geographic trend similar to those for the individual compounds identified. In Lakes Ladoga and Saimaa, the concentrations of EOX and chlorinated hydrocarbons in the blubber were dependent on the age and sex of the seals, but no such relationship was observed in samples from the White Sea.

Finnish lake fisheries and conservation of biodiversity: coexistence or conflict?

The conservation of biodiversity in aquatic habitats has become an increasingly important challenge in the management of water resources. In addition to the complexity of the lake fishery and the management structure, the popularity of gill net fishing, in particular, has brought problems when re‐establishing populations of Arctic charr, Salvelinus alpinus (L.), collecting genetically sustainable numbers of spawners of the land‐locked salmon, Salmo salar m. sebago (Girard), and increasing the population of the Saimaa ringed seal, Phoca hispida saimensis (Nordq.) to a sustainable level in the Vuoksi watercourse, south‐east Finland. The attitudes towards protection among the users and other interested parties vary. In order to enhance the coexistence of the lake fishery and endangered species over large water areas, improved institutional linkages are needed among the local, regional and governmental levels of the fragmented decision‐making regime. Environmental interests should also be integrated into the communication structure.

Short-code paleolimnological investigation of Lake Pihlajavesi in the Saimaa Lake complex, eastern Finalnd: assessment of habitat quality of an endemic and endangered seal population

A short-core paleolimnological investigation was carried out to acquire knowledge of the recent history of Lake Pihlajavesi, Saimaa Lake complex, and define its natural state before cultural disturbances. In the natural state, with negligible human interference, the basin was oligotrophic and oxygen-rich. The bioproductivity in the littoral zone was low and the profundal benthic quality was good according to Wiederholm's Benthic Quality Index.Based on diatom analyses, no significant changes have taken place in the phytoplankton communities during the past decades. Sedimentary chironomid communities reveal, however, slight changes on profundal life in the Pihlajavedenselka basin, near the main pollution sources, whereas there were no significant changes in the outer basin. Three stages could be distinguished in the pollution history of Pihlajavedenselka: (1) 'The natural state' up until the 1960s, (2) 'the period of increasing loading' during the 1960s and 1970s, and (3) 'the recovery of the basin' during the past two decades.Untreated municipal waste water from the town of Savonlinna was partly responsible for the commencement of eutrophication in the Pihlajavedenselka basin in the 1960s. The paper and pulp industry in Varkaus, some 40 kilometres upstream from Lake Pihlajanvesi, has also increased eutrophication, especially during the worst period of water quality in the 1960s and 1970s. More effective waste water purification has markedly reduced effluent loading and led to a general recovery of the area. Neverthless the effects of slight nutrient loading can still be seen, especially in littoral bioproductivity.Our paleolimnological data indicate that the present ecosystem will offer living conditions for the endemic Saimaa ringed seal population that are similar to those that existed prior to human disturbances.

The diet of the Saimaa ringed seal Phoca hispida saimensis

The diet of the Saimaa ringed seal Phoca hispida saimensis Nordquist, 1899 was studied by the analysis of stomach contents and by feeding trials with a captive seal. Nine prey species were found in the stomachs, the most important being small schooling fish species: perch Perca fluviatilis, roach Rutilus rutilus, vendace Coregonus albula, smelt Osmerus eperlanus and ruff Acerina cernua. The importance of crustaceans in the diet of the ringed seal in Lake Saimaa is insignificant. Length of the intestinal tract of the Saimaa ringed seal is relatively shorter than those of marine ringed seals. In cafeteria tests on one captive seal the preferred fish species were vendace and smelt. The captive seal displayed clear seasonal variation in feeding activity. The consumption of fish was lowest in springtime and highest in autumn and winter.

Status and biology of Saimaa (<i>Phoca hispida saimensis</i>) and Ladoga (<i>Phoca hispida ladogensis</i>) ringed seals

Saimaa (Phoca hispida saimensis) and Ladoga (P. h. ladogensis) seals are subspecies of ringed seals that live in freshwater lakes. The founding populations for these two subspecies became separated from Arctic ringed seals (P. h. hispida) during the last ice age. The Saimaa seal population currently numbers approximately 200 seals with 36 - 40 pups born annually. The Ladoga seal population contains at least 5,000 seals. The weight of adult animals in Lake Saimaa is 45-100 kg (mean 62 kg) and in Lake Ladoga adults weigh 32-56 kg (mean 47 kg). The lanugo of Saimaa seals is grey. Normally pups in Lake Ladoga are born with white lanugo, although some pups have been found that have black hairs in the natal pelt. Adult Saimaa seal vary a lot in colour, ranging from dark to pale animals, but all colour morphs have regular ringed patterns on the pelt. Ladoga seals are usually quite dark, with irregular, light ringed patterns. Saimaa seals are usually found hauledout alone or in pairs along shorelines. Ladoga seals haul out in herds of up to 300 animals, and are very vocal when they are hauled out. The lairs of Saimaa seals are situated in snowdrifts adjacent to shorelines of islets, which are the only places where snow piles up in Lake Saimaa. Most Ladoga seal lairs are situated near hummocked or ridged ice along the shoreline of the lake, but some lairs are also found along the shorelines of islets in northern Lake Ladoga. Saimaa seals are an endangered population. The main threats to these seals are fisheries conducted using nets and destruction of breeding habitat. The Ladoga seal is vulnerable, and it also is threatened by fishing. Mercury in both lakes presents an anthropogenic risk factor, but present levels probably do not affect the breeding of either seal population.

Estimating the demographic effective population size of the Saimaa ringed seal (Phoca hispida saimensis Nordq.)

A common ‘rule of thumb' in conservation biology is that populations of more than 100 individuals are not threatened by demographic stochasticity alone. However, the effect of demographic stochasticity on population survival may be strengthened if the population has a non-homogeneous demography. A recently developed measure, the demographic effective population size ND, scales population size by taking the differential contribution of individuals into account. We exemplify the estimation of ND with the current population of the Saimaa ringed seal, comprising about 200 individuals. The estimate of ND is shown to be dependent on how independently individuals can be assumed to reproduce. Completely independent reproduction leads to ND∼ 250, suggesting a safe future for the population. However, when acknowledging the potential of breeding failure due to habitat limitation and difficulties of dispersal among the different subareas of Lake Saimaa, ND lies in an alarming range from six to 30 individuals. The effective means to increase the ND value are limited. Although subdivision itself decreases the value of ND, improving dispersal of individuals is shown to be of limited aid. Instead, the most effective way to enhance future prospects of the Saimaa seal population is to improve pup survival to maturity.

Mercury Pollution and the Saimaa Ringed Seal (Phoca hispida saimensis)

Mercury concentrations in the hair and various tissues of the Saimaa ringed seal were monitored from 1980 to 1995. In the liver, muscle and kidney of weaned pups mercury concentrations dropped in the middle of the 1980s. In the natal hair and liver of young pups, however, no clear decrease was seen. In the natal hair and main fish prey species of the seals mercury concentration were highest in areas of humic water. Mercury concentration in the liver of adults has not changed significantly since 1981. Age of the seal is clearly correlated with mercury concentration in the liver. Shortage of selenium is assumed to be one reason for high concentrations of mercury in muscle. The mercury concentration in hair decreased markedly in an adult seal in captivity, after giving selenium. Based on these findings, one reason for the decrease in population density of the Saimaa seal in this century may have been mercury pollution.

Mercury pollution and the Saimaa ringed seal ( phoca hispida saimensis)

Mercury concentrations in the hair and various tissues of the Saimaa ringed seal were monitored from 1980 to 1995. In the liver, muscle and kidney of weaned pups mercury concentrations dropped in the middle of the 1980s. In the natal hair and liver of young pups, however, no clear decrease was seen. In the natal hair and main fish prey species of the seals mercury concentration were highest in areas of humic water. Mercury concentration in the liver of adults has not changed significantly since 1981. Age of the seal is clearly correlated with mercury concentration in the liver. Shortage of selenium is assumed to be one reason for high concentrations of mercury in muscle. The mercury concentration in hair decreased markedly in an adult seal in captivity, after giving selenium. Based on these findings, one reason for the decrease in population density of the Saimaa seal in this century may have been mercury pollution.