Eero Helle

Reproduction in the raccoon dog in Finland

Reproduction in the raccoon dog ( Nyctereutes procyonoides ) was studied on the basis of 632 female carcasses in Finland in 1986–1990. In Finland, raccoon dogs usually mate from February to April, with a peak in March. Differences occurred both regionally and with respect to age, with older females breeding earlier than younger ones. Fecundity (number of corpora lutea per breeding female) averaged 11.5, with variation in fecundity occurring both annually and regionally, but not in relation to age of females. Embryonic litter size averaged 9.6 and was highest among females 3–5 years old. Litter size at birth averaged 8.8 and also peaked at 3–5 years of age. Loss of ova and preimplantation mortality averaged 15% in southern Finland, but was as high as 30% in the northeastern part of the study area. Because fetal mortality averaged an additional 5–10%, total prenatal mortality may surpass 20%. The proportion of reproducing females averaged 78%, increasing with age, as did productivity (number of young per female), increasing from 5.5 at 1 year of age to 8.2 at ≥3 years. Reproductive value was highest among 2-year-old females. Reproduction in raccoon dogs is strongly affected by climate and weather, and the availability of food (voles and berries) in relation to population density. The abundance of food and population density influence growth (including sexual maturation) of young raccoon dogs and their condition (fat reserves). In adult females, condition mostly affects annual variation in litter size at birth, whereas, in young females, it affects the regional variation in the proportion of reproducing females.

Habitat selection of adult moose Alces alces at two spatial scales in central Finland

The habitat selection criteria of moose Alces alces at several scales are the basic sets of information needed in moose management planning. We studied moose habitat use in central Finland during 1993–1996 using data from radio collared moose, satellite image based forest and land cover data, and applied the principles of compositional analysis. The habitat compositions of 54 home ranges (10 males during summer, six males during winter, 23 females during summer and 15 females during winter) were first compared with the overall landscape. The habitat compositions around moose locations within their home ranges were then compared with the habitat composition of the home range. Seasons and sexes were compared at both scales. In summer, there was only a slight difference between moose home ranges and the overall landscape. Based on tree species composition, home ranges are located in slightly more fertile areas than the overall landscape. Within their home ranges, moose favoured non-pine dominated habitats and mature forests, and avoided human settlements. In winter, the moose home ranges included significantly more pine-dominated plantations and other young successional stages than the overall landscape. The role of pine-dominated peatland forests/ shrub land was especially pronounced in winter. Winter home ranges included less agricultural land and human settlements than the overall landscape, probably due to the more distant location of important winter habitats from man-made landscapes. Within the home ranges, both sexes used non-pine dominated habitats more, and mature forests and human settlements less than expected. At the home range scale, there were no statistical differences between the sexes with respect to habitat use in either season. Within their home ranges, males and females used slightly different habitats during both seasons, suggesting spatially segregated habitat use by the individual sexes. The difference is more clear in winter when males tend to use more pine-dominated, young successional habitats than females. Compared to the situation in the summer, winter ranges are located in slightly more pine-dominated habitats with fewer settlements and agricultural fields. The shift in habitat use between the two seasons is more pronounced with respect to habitat use within the home range. Our results indicate that moose habitat selection criteria vary among different hierarchical levels of selection. We stress the importance of multi-scale assessment of the habitat and other resource selection of animals.

Comparison between spring and autumn infection by Corynosoma (Acanthocephala) in the ringed seal Pusa hispida in the Bothnian Bay of the Baltic Sea

Corynosoma spp. (Acanthocephala) infection in ringed seals ( Pusa hispida ) is compared in spring and in autumn in the Bothnian Bay, northern Baltic Sea. The material consists of more than 13400 specimens: 7590 from the intestines of 13 seals captured in April and May 1978 and 5850 from 29 seals captured in October and November. Corynosoma strumosum infection had approximately the same intensity in spring and autumn (mean 76 and 66 individuals/infected seal, maxmum 313 and 324 individuals, respectively). C. semerme specimens, on the other hand, were 37 times more numerous in spring than in autumn (504 compared with 136/infected seal, maximum 1700 and 1230 individuals, respectively). The ratio of C. strumosum to C. semerme was 1:6·3 in spring and 1:2·0 in autumn, as calculated from the total material. Corynosoma infection was more recent on average in spring than in autumn, as judged both from the proportion of males and immature females and from the distribution of C. semerme in the intestine. The feeding habits of the ringed seals and the rate of development of Corynosoma infection are discussed.

Age Structure, Mortality, and Sex Ratio of the Raccoon Dog in Finland

We studied the age, sex structure, and mortality of a population of the raccoon dog ( Nyctereutes procyonoides ) in southern Finland from 1986 to 1990. The sex ratio was 1:1. There were no sexual differences in age structure. In the course of the study, the population declined slightly, which was taken into account when life tables were calculated. The age structure of the captures in autumn were rather stable in successive years. Life tables were calculated by two methods; by treating the captures from the breeding season (March–April) as a random sample of the population, and by treating the year-round captures (from August to May) as a sample of the animals that die in the course of 1 year. The two life tables did not differ statistically; the annual mortality rate of the population in southern Finland was 80.5% (54 and 51% for adults, and 88 and 89% for juveniles, respectively). According to the life table based on the random sample of the population, the mortality rate was lowest among 2–4-year-old raccoon dogs and increased after 5 years of age; maximum life span was 7–8 years. Because of heavy pressure from hunting, mortality among juveniles was high, which may have resulted in a high rate of reproduction.

Contracaecum osculatum (Nematoda: Anisakidae) in fish and seals in Bothnian Bay (northeastern Baltic Sea)

Abstract The occurrence of C. osculatum in 7400 fish specimens of 30 species and in two seal species is reported from Bothnian Bay, Baltic Sea. Seven fish species were infected with C. osculatum, the highest prevalences occurring in the salmon, bull-rout, burbot and cod (20%, 20%, 16% and 15%, respectively). Prevalences tended to increase in the larger fish, but no seasonal variations were found in either the prevalence or the intensity of infection. C. osculatum occur and mature only accidentally in the resident seal species, the ringed seal (Phoca hispida botnica), but a mean of 640 worms were found in the grey seal (Halichoerus grypus) with a maximum of 1244 worms. Grey seals regularly visit the present study area for a few weeks in late spring and it is thought that these serve to maintain the C. osculatum infection in the fish of the area. The nematodes were found in the stomachs of the grey seals, where they tended to occur in aggregations of both third- and fourth-stage larvae and adult worms simultaneously. The presence of third-stage larvae demonstrates that the origin of the C. osculatum infection in these seals may also be in Bothnian Bay. in addition to the more southerly areas where grey seals are to be found for most of the year.

Experimental infection of laboratory rats with Corynosoma semerme (Acanthocephala).

Ten albino rats injected with hydrocortisone were infected with 36-66 cystacanths of Corynosoma semerme in order to study the course of infection in a warm-blooded animal. Surveys were carried out 2, 5, 8, 14, 18, 21 and 28 days after infection. Recovery decreased from 60% after 2-5 days to 22% after 28 days. The proportion of males dropped markedly before the 8th day of infection. The worms were concentrated in the latter half of the intestine, the males being in a more anterior location on average. The males matured between the 2nd and 5th day of infection. Disintegrated ovaries were observed in some of the 2-day-old females, but mature free ovaries were seen only in 5-day-old females. By the 14th day many females contained fully developed eggs, but it was only after the 18th day that the number of eggs increased considerably. Male worms were not encountered in the 4-week-old infection. The females were longer than the males. In the present study, experimental infections are compared with other acanthocephalan infections in both birds and mammals.

Population ecology of the raccoon dog in Finland - a synthesis

The population ecology of the raccoon dog Nyctereutes procyonoides was investigated in Finland from 1973 to 1992. Annual mean temperature explained most of the regional variation in the growth rate and present density of the population. Climate explained most of the regional variation in the productivity of the raccoon dog population; the length of the annual snow-free period accounted for most of the regional variation in the weight and fat reserves of young females in late autumn which, in turn, affected the proportion of reproducing females in the population the following spring. Of the independent variables examined, the abundance of wild berries is the dominating factor in explaining the annual variation in density; mortality is highest during the first year of life and the availability of berries probably affects the mortality of juveniles during autumn and winter. The abundance of voles and the population density of raccoon dogs in spring affects the fat reserves of adult females which, in turn, affect their litter size. The productivity of adult females is density dependent, and, thus, regulates population density to some extent. Changes in population size seem to be density dependent after the population peaked around the mid-1980s.