Mervi Kunnasranta

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.

Spatial and temporal variation in genetic diversity of an endangered freshwater seal

Molecular-genetic assessments of demographic history, population structure, and loss of genetic variation in small natural populations are often hampered by a lack of information on initial diversity, isolation time, and migration rates. The landlocked population of currently less than 300 ringed seals inhabiting Lake Saimaa in southeastern Finland offers a unique model for studying these questions in small populations. It has remained completely isolated since the last ice age, information on its initial genetic diversity can be inferred from the large marine source population in the Baltic Sea, and its ecology is well studied. We analyzed the mitochondrial DNA diversity of 215 Saimaa ringed seals spanning three decades in order to assess long- and short-term changes in the gene pool of this critically endangered subspecies. The mtDNA diversity of the Saimaa ringed seal is low, consisting of only eight haplotypes. Nevertheless, coalescent simulations show that the diversity is unexpectedly high when contrasted with the over 800 generations of isolation and the estimated historical carrying capacity of the lake. In the short term, marked temporal and spatial differentiation was observed among three decades and four regions of Lake Saimaa, suggesting extremely low effective subpopulation sizes and limited migration of females within the lake. Our study strongly suggests that enhancing gene flow and population growth is crucial for maintaining the remaining genetic diversity of the Saimaa ringed seal.

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.

Causes and consequences of fine-scale population structure in a critically endangered freshwater seal

BackgroundSmall, genetically uniform populations may face an elevated risk of extinction due to reduced environmental adaptability and individual fitness. Fragmentation can intensify these genetic adversities and, therefore, dispersal and gene flow among subpopulations within an isolated population is often essential for maintaining its viability. Using microsatellite and mtDNA data, we examined genetic diversity, spatial differentiation, interregional gene flow, and effective population sizes in the critically endangered Saimaa ringed seal (Phoca hispida saimensis), which is endemic to the large but highly fragmented Lake Saimaa in southeastern Finland.ResultsMicrosatellite diversity within the subspecies (HE = 0.36) ranks among the lowest thus far recorded within the order Pinnipedia, with signs of ongoing loss of individual heterozygosity, reflecting very low effective subpopulation sizes. Bayesian assignment analyses of the microsatellite data revealed clear genetic differentiation among the main breeding areas, but interregional structuring was substantially weaker in biparentally inherited microsatellites (FST = 0.107) than in maternally inherited mtDNA (FST = 0.444), indicating a sevenfold difference in the gene flow mediated by males versus females.ConclusionsGenetic structuring in the population appears to arise from the joint effects of multiple factors, including small effective subpopulation sizes, a fragmented lacustrine habitat, and behavioural dispersal limitation. The fine-scale differentiation found in the landlocked Saimaa ringed seal is especially surprising when contrasted with marine ringed seals, which often exhibit near-panmixia among subpopulations separated by hundreds or even thousands of kilometres. Our results demonstrate that population structures of endangered animals cannot be predicted based on data on even closely related species or subspecies.

Application of change-point analysis to determine winter sleep patterns of the raccoon dog (Nyctereutes procyonoides) from body temperature recordings and a multi-faceted dietary and behavioral study of wintering

BackgroundA multi-faceted approach was used to investigate the wintertime ecophysiology and behavioral patterns of the raccoon dog, Nyctereutes procyonoides, a suitable model for winter sleep studies. By utilizing GPS tracking, activity sensors, body temperature (Tb) recordings, change-point analysis (CPA), home range, habitat and dietary analyses, as well as fatty acid signatures (FAS), the impact of the species on wintertime food webs was assessed. The timing of passive bouts was determined with multiple methods and compared to Tb data analyzed by CPA.ResultsRaccoon dogs displayed wintertime mobility, and the home range sizes determined by GPS were similar or larger than previous estimates by radio tracking. The preferred habitats were gardens, shores, deciduous forests, and sparsely forested areas. Fields had close to neutral preference; roads and railroads were utilized as travel routes. Raccoon dogs participated actively in the food web and gained benefit from human activity. Mammals, plants, birds, and discarded fish comprised the most important dietary classes, and the consumption of fish could be detected in FAS. Ambient temperature was an important external factor influencing Tb and activity. The timing of passive periods approximated by behavioral data and by CPA shared 91% similarity.ConclusionsPassive periods can be determined with CPA from Tb recordings without the previously used time-consuming and expensive methods. It would be possible to recruit more animals by using the simple methods of data loggers and ear tags. Hunting could be used as a tool to return the ear-tagged individuals allowing the economical extension of follow-up studies. The Tb and CPA methods could be applied to other northern carnivores.

Breeding habitat and lair structure of the ringed seal (Phoca hispida ladogensis) in northern Lake Ladoga in Russia

Abstract The breeding habitat and lair structures of the ringed seal (Phoca hispida ladogensis) were studied by snowmobile expeditions in northern Lake Ladoga, Russia, during 1996 to 1999. Mostly flat ice and no large pack ice existed in northern Lake Ladoga during this study. All birth lairs and 88% of haul-out lairs were located in snowdrifts in the shorelines of islands or islets and 12% of the haul-out lairs occurred in pressured ice ridges. Some large haul-out lairs had been used communally by the seals. A total of 15% of the lairs observed had been attacked or marked by red fox (Vulpes vulpes), wolf (Canis lupus) or unidentified canines. The colour of the lanugo fur of the Ladoga ringed seal pup appeared to be dark grey. We conclude that the northern part of Lake Ladoga is an active breeding area for the ringed seal, which attests conservation needs for this area.

Estimating and Mitigating Perinatal Mortality in the Endangered Saimaa Ringed Seal (Phoca hispida saimensis) in a Changing Climate

The ringed seal (Phoca hispida) is dependent on sufficient ice and snow cover for a breeding habitat. Therefore, climate change has a negative effect on pup survival. We developed methods to estimate perinatal mortality and to mitigate the effects of mild winters on the critically endangered subspecies (P. h. saimensis). Underwater surveys were used for collecting pup carcasses and placentas. Lanugo pup mortality was 13.5% and Brucella sp. was not found in the placentas. Camera traps showed sporadic human and medium-sized carnivore activity in the breeding habitat. Although carnivore activity was most intensive at lair sites, no penetration of the lairs was observed. We developed a method to mitigate the effects of poor snow cover by piling up snowdrifts (n = 117) at potential lair sites. Seals subsequently occupied 62% of these snow drifts. We suggest that the methods developed in this study should be implemented to conserve the Saimaa ringed seal.

The Effects of Sex and Season on Home Range in European Hedgehogs at the Northern Edge of the Species Range

Limited data exist on ecology of European hedgehog (Erinaceus europaeus) at the northern edge of the species’ range. In our study, spatial analysis using radio-tracking data from Finland showed that sex and season had significant effects on the homerange size of hedgehogs. Although males were heavier than females, body weight had no effect on home-range size. Total home ranges (male 98, female 55 ha) were larger than those in southern areas. Thus, male home ranges were larger than those of females during the mating (male 72, female 21 ha) and post-mating seasons (male 48, female 20 ha), but the differences were small and reversed before hibernation (male 17, female 29 ha). Home ranges of individuals of both sexes overlapped, but females shared core areas with other females only during the mating season. Our results imply possible differences in hedgehog ecology probably due to a less productive and harsh northern habitat.

Demographic Structure and Mortality Rate of a Baltic Grey Seal Population at Different Stages of Population Change, Judged on the Basis of the Hunting Bag in Finland

We examined the demographic structure and mortality rate of the Baltic grey seal (Halichoerus grypus) population from the early 2000s when the population increased rapidly to the late 2000s when the growth rate slowed down. We calculated life tables based on the age structure of hunted grey seals in the Finnish sea area. The catch was treated as a sample of the dying part of the population. The catch was male biased and the proportions of female pups and mature males in the catch increased from the early to late 2000s. Annual mortality rate of the youngest age classes was high and higher among males than females, which resulted in low sex ratio (males to females) of the population. Sex ratio was, however, higher in the latter years due to the increased mortality rate of females, especially those < 10 years of age. Accordingly, the proportion of mature females in the population decreased and relatively fewer pups were produced during the late 2000s than in the early 2000s.

Demographic histories and genetic diversities of Fennoscandian marine and landlocked ringed seal subspecies

Island populations are on average smaller, genetically less diverse, and at a higher risk to go extinct than mainland populations. Low genetic diversity may elevate extinction probability, but the genetic component of the risk can be affected by the mode of diversity loss, which, in turn, is connected to the demographic history of the population. Here, we examined the history of genetic erosion in three Fennoscandian ringed seal subspecies, of which one inhabits the Baltic Sea ‘mainland’ and two the ‘aquatic islands’ composed of Lake Saimaa in Finland and Lake Ladoga in Russia. Both lakes were colonized by marine seals after their formation c. 9500 years ago, but Lake Ladoga is larger and more contiguous than Lake Saimaa. All three populations suffered dramatic declines during the 20th century, but the bottleneck was particularly severe in Lake Saimaa. Data from 17 microsatellite loci and mitochondrial control-region sequences show that Saimaa ringed seals have lost most of the genetic diversity present in their Baltic ancestors, while the Ladoga population has experienced only minor reductions. Using Approximate Bayesian computing analyses, we show that the genetic uniformity of the Saimaa subspecies derives from an extended founder event and subsequent slow erosion, rather than from the recent bottleneck. This suggests that the population has persisted for nearly 10,000 years despite having low genetic variation. The relatively high diversity of the Ladoga population appears to result from a high number of initial colonizers and a high post-colonization population size, but possibly also by a shorter isolation period and/or occasional gene flow from the Baltic Sea.