The determination of the age composition of a population is considered to be a fundamental parameter for the analysis of life-history strategy of the species. In the Tayassuidae, the determination of relative age has been primarily based on molar tooth wear, sometimes combined with other external characteristics, such as hair color or body size. The present study examined the dental composition of white-lipped peccariesTayassu pecari (Link, 1795) . Through the determination of the erupted dental pattern and its relation to the body weight of the animal, six age classes were established. The presence of molar teeth was considered the most accurate parameter for establishing age classes for white-lipped peccaries.
The abundance of the spawning population of roach females from the coastal lakes Gardno (2 468 ha) and Łebsko (7 140 ha) located in the Słowiński National Park was estimated for the 1987-1992 period. Following bream, roach is the second most common cyprinid species in regulated fisheries catches. The size of the spawning population was estimated using Virtual Population Analysis and long-term fisheries statistics. Female roach dominated the exploited population at 62.4% in Lake Gardno and 64.3% in Lake Łebsko. During the analyzed period, more roach females were caught in Lake Gardno, which is more than twice as small as Lake Łebsko. Of the generations analyzed (1985, 1986, 1987, 1988, 1989 and 1990), more abundant years occurred in Lake Gardno. The most abundant generation in the two lakes was that of 1985, and following it, each subsequent generation was weaker than the preceding had been.
Dreissena polymorpha inhabits about 46.5% of the bottom area in Lake Dabie. It is most abundant in the northern part of the lake and sporadically occurs in its southern part. The average density of the zebra mussel is 891 individuals/m², while its wet weight is 1374 g/ m². In the settled areas the density of the zebra mussel reaches 1734 individuals/ m². There were presently established 7 age-groups from 0 to 6+. The highest number of specimens occurred in the age-groups between 1+ and 3+, while the lowest number - in the groups 0, 5 and 6+. Strong eutrophication and pollution of Lake Dabie on its southern side, combined with sedimentation of the extensive amounts of seston carried in by the Płonia and Regalica rivers, do not create favourable conditions for development of Dreissena. D. polymorpha plays a very positive role in the lake ecosystem through its biofiltrating action, contributing thus to an increase of water clarity and to limitation of phytoplankton development through cumulating nutrients in its biomass. Electrophoretic analysis of 9 enzymatic loci revealed strong polymorphism of the studied population of the zebra mussel: percent of polymorphic loci - 100, mean number of alleles in locus – 3.4, coefficient of expected heterozygosity per locus in the population, HS - 0.335, percentage of separate genotypes - 69%, in this number unique genotypes - 58%. A very strong scattering of the alleles was stated within the entire population. In each aggregation, on average, 90% of the specimens have a separate genotype. Each of the five defined groups of D. polymorpha, representing profiles I-V, respectively, had similar genetic composition. The values of the genetic similarity among the studied groups of the zebra mussel ranged from 0.96 to 0.99.
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