A total of 16 fish species have been identified in the Veleka River and its tributaries the Mladezhka River and the Aydere River. Three of the species are included in the Red Data Book of Bulgaria: Anguilla anguilla, Chalcalburnus chalcoides and Rutilus frisii. Mean abundance (N) and mean biomass (B) of fishes were as follows: 3093 ind. ha-1 and 68.19 kg ha-1 in the Veleka River, 1220 ind. ha-1 and 16.73 kg ha-1 in the Mladezhka River, and 1025 ind. ha-1 and 41.18 kg ha in the Aydere River. The values obtained were much lower than the values of N and B of fishes in nine other Bulgarian rivers. The main reasons for the low fish abundance and biomass in the Veleka River and its tributaries were the intensive development of tourist industry in the region and the intensive, practically uncontrolled commercial and sport fishing and poaching.
This study in Lithuania showed that the abundance dynamics of the common dormouse (Muscardinus avellanarius) populations were comparatively “smooth”, without outbreaks and crashes. Decreases and increases of abundance continued for some years, and abundance differed no more than three-fold in two successive years. A close negative correlation was revealed between spring population density and percentage of juveniles in the autumnal population. The last parameter is a consequence of reproduction success, which determined the scale of population increase in autumn and was due to several factors. Among them, proportion of breeding adult females had the greatest significance and was inversely proportional to population density in spring. Some young-of-the-year females usually joined the breeding process, when population density was low. The proportion of late breeding cases, when juveniles were born in September, was also negatively correlated with spring population density. The number of litters produced by one female during the season, and the average litter size also influenced reproduction success. The negative correlation between population density and reproduction success shows the presence of a reproduction success based pattern of density dependent self-regulation in M. avellanarius in the populations investigated.