Assessment of herb field mouse (Sylvaemus uralensis) migration in the area of the East Urals Radioactive Trace using measurements of bone-seeking Sr.

The dynamics of rodent population in the area of East Urals Radioactive Trace (EURT) is one of the controversial issues, which are of key importance for the radiobiological and radioecological interpretation of the observed radiation effects. The objective of the paper is to evaluate the probability of migration in population of the herb field mouse (Sylvaemus uralensis Pall., 1811) based on Sr activity concentrations in the mouse bones. Radiometric data for bones of 768 mice captured at 9 sites in the EURT territory (with different environmental contamination levels) in 2001-2012 were used. The distribution of bone-seeking Sr in the juvenile age group of mice is used as a model of the width of radionuclide distribution in the bones of permanent inhabitants. Comparison of the model predictions and observations in different age and functional groups within the population structure allows simulating the probability of migration and evaluating the fraction of migrants. It is shown that the accumulation of Sr in bones correlates with soil contamination at the capture sites. Individual variability in the specific activity of Sr in the skeleton tends to increase with the age of animals. The rate of herb field mouse migration is estimated as 7 and 15% per year (for underyearlings and wintered individuals, respectively). The animals captured in the EURT area (all animals, including juvenile individuals) are "diluted" with animals from non-contaminated territories by 5-12%. The average half-time of substitution of the exposed population by migrants from non-contaminated territories is 8 years. Today, the fraction of descendants of the animals, that for generations have permanently inhabited the EURT territory since 1957, is negligible (on average-1.2% and not exceeding 17%). The proposed method of probabilistic analysis of Sr in the bones could be used to study migration activity of other species of rodents.