A total of 1642 individuals of the Chinese mitten crab, Eriocheir sinensis caught in [2001][2002] in the Odra estuary, were measured. The carapace width was found to range from 46.68 to 92.31 mm (mean width 66.61 ± 7.33 mm); the mean carapace widths of females and males were 65.40 ± 6.82 mm (46.68-88.85 mm) and 67.96 ± 7.66 mm (47.04-92.31 mm), respectively. There were distinct differences in the numbers of individuals caught in different months. The highest number of crabs (85.44% of all individuals) was caught in autumn, as a consequence of reproductive migration. In the total number of 1642 specimens examined, males were slightly dominant (51.4%), in particular in October (55.31%) and November (52.01%). Females dominated in spring and summer and contributed 57.2-64.7%. RÉSUMÉUn total de 1642 individus du crabe chinois Eriocheir sinensis capturés en 2001-2002 dans l'estuaire de l'Odra ont été mesurés. La largeur de la carapace était comprise entre 46,68 et 92,31 mm (largeur moyenne 66,61 ± 7,33 mm); la largeur moyenne de la carapace des femelles et des mâles était de 65,40 ± 6,82 mm (46,68-88,85 mm) et 67,96 ± 7,66 mm (47,04-92,31 mm), respectivement. Des différences notables ont été observées dans les nombres d'individus capturés suivant le mois. Le nombre le plus élevé de crabes (85,44% de tous les individus) a été récolté en automne, suite à la migration de reproduction. Sur le nombre total des 1642 spécimens examinés, les mâles étaient légèrement dominants (51,4%), en particulier en octobre (55,31%) et novembre (52,01%). Les femelles dominaient au printemps et en été, dans la proportion de 57,2-64,7%.

The results of an analysis of the autumn diet of the Chinese mitten crab, Eriocheir sinensis, are presented and the crab's effects on the most common species of the flora and fauna of the River Odra estuary are assessed. Examination of crab gut contents showed the diet to be composed of detritus (59.6%), vascular plants (10.7%), and animals, mainly copepods and chironomid larvae (10.4%). The crabs, kept for 2 months in tanks under abiotic and biotic conditions similar to those prevailing in the Odra estuary, diminished the biomass of aquatic plants (particularly that of Elodea canadensis) by almost 12%, and that of aquatic macroinvertebrates (26% reduction of chironomid biomass and more than 21% reduction of tubificid biomass), which, at a high abundance of the crab, may have an adverse effect on the composition of species of plants and animals in the estuary. RÉSUMÉLes résultats des analyses du régime alimentaire d'automne du crabe chinois, Eriocheir sinensis, sont présentés, et les effets de ce crabe sur les espèces les plus communes de la flore et de la faune dans l'estuaire de la rivière Odra (Pologne) sont évalués. L'étude des contenus stomacaux du crabe montrent que le régime alimentaire est composé de détritus (59,6%), de plantes vasculaires (10,7%), et d'animaux, essentiellement copépodes et larves de chironomes (10,4%). Les crabes maintenus pendant 2 mois en aquariums sous des conditions abiotiques et biotiques similaires à celles existant dans l'estuaire de l'Odra, diminuent la biomasse de plantes aquatiques (particulièrement celle d' Elodea canadensis) d'au moins 12% et celle des macroinvertébrés aquatiques (26% de réduction de chironomidés et plus de 21% de réduction des tubificidés), ce qui, avec une forte abondance de crabes, pourrait avoir des effets adverses sur la composition spécifique des plantes et des animaux dans l'estuaire.

ABSTRACT. The aim of the study was to determine individual absolute and relative fecundity in vendace, Coregonus albula (L.), populations from four Western Pomeranian lakes that differ morphometrically and trophically. The highest mean total length and individual weight were recorded in the fish from the mesotrophic lakes Iñsko (229.1 mm and 106.6 g, respectively) and Miedwie (228.1 mm and 105.1 g, respectively). The highest individual absolute fecundity in particular age groups as well as individual relative fecundity were noted in the fish from Lake Miedwie (6635-24620 eggs per female and 10756-11609 eggs per 100 g female body weight, respectively), while the lowest values of these parameters were confirmed in fish from Lake Glinna (4782-6087 eggs per female and 6406-6953 eggs per 100 g female body weight). A high, statistically significant correlation between absolute fecundity and total fish length and a slightly lower correlation between absolute fecundity and fish age were noted in all of the populations studied.

The vendace, Coregonus albula (L.), is one of the most valuable fish species caught in Polish lakes. The factors contributing to its high value are: high quality meat, fast growth rate, shoaling behaviour, and high market value. These qualities explain why, despite the high environmental requirements of this species, its catch had been increasing systematically in Poland, in the 1980s, reaching almost 600 t per year. However, due to the transformation of the fishing industry, the vendace fishery decreased twofold in the 1990s (Leopold and Wo³os 1999). The disappearance of Coregonus sp. in lakes has also been related to adverse changes resulting from . Vendace are found in 44 out of 1575 lakes of Polish western Pomerania (Filipiak and Raczyñski 2000), although only 23 of them are explored by professional fishermen (Czerniejewski and Filipiak 2001). Unfortunately, due to a lack of knowledge on the biological features of vendace populations inhabiting these waters it is impossible, in many cases, to implement a reasonable fisheries management. We decided to focus our attention on three, hitherto not studied, vendace populations inhabiting lakes Pe³cz Wielki, Bytyñ Wielki and We³tyñ (Table 1) and to determine the biological features of those fish, in particular their age structure, growth rate, and condition. MATERIALS AND METHODSVendace, Coregonus albula (L.), collected for the presently reported study were caught at night with a 24-mmmesh-size gillnets in lakes: Pe³cz Wielki (136 specimens; ACTA ICHTHYOLOGICA ET PISCATORIA (2006) 36 (1): [65][66][67][68][69][70][71][72] Background. Vendace, Coregonus albula (L.), is one of the most valuable components of Polish lake ichthyofauna. The vendace from different lakes differ in their principal vital characteristics (such as growth rate etc.) and it is therefore crucial to determine those characteristics from different throphic types of lakes in order to implement proper measures of fisheries management for those coregonids. The aim of the present paper was therefore to learn principal biological features of vendace populations representing three different Pomeranian lakes. Materials and Methods. Comparative biological studies were carried out on 136 vendace from Pe³cz Wielki Lake, 304 from Bytyñ Wielki Lake, and 62 from We³tyñ Lake (Pomerania Lakeland) collected within 2002-2003. The age and growth rate of the fish were determined from scales. Fulton's condition factor and the total length-weight relation were used to determine fish condition. Results. Gillnet selectivity influenced fish age structure and size. For example, among 502 vendace obtained, in total, from the three lakes, 75.7% (380 specimens) were 2+. The results of back-calculations and the parameters of von Bertalanffy's growth equation revealed distinct disproportions in the total length in individual age groups (Pe³cz Wielki Lake: L t = 213.22[1 -e -0.49576(1 + 1.055013) ]; Bytyñ Wielki Lake: L t = 219.17[1 -e -0.733553(1 + 0.040147) ]; We³tyñ Lake: L t = 255.08[1 -e -0.571108(1 + 0.023036) ]) Slower leng...

Mussel shells are often found in archaeological excavations and can provide information useful for ecological reconstruction and assessment of anthropogenic impact on waters. In this study, two sample groups of swollen river mussel (Unio tumidus) which occurred during the Early Middle Ages (EMS) and currently (MS) in the Oder river estuary (Baltic basin) were compared. Allometric shell growth, morphological characteristics of the shell (length, width, height and thickness), age structure and growth of mussels were analysed using the von Bertalanffy equation. All three types of allometric growth (isometry and both positive and negative allometry) were observed in the studied mussels. In both groups, typical values of shell length, width, height and thickness were recorded. However, higher values of these morphological characteristics were recorded in the EMS group. Moreover, the EMS group, compared with the MS group of U. tumidus, was characterised by a higher longevity (12 and 10 years, respectively) and asymmetric length (L∞) (93.09 and 83.23 mm, respectively). Both groups of mussels had a similar growth rate (k). Larger shell sizes in the EMS group were probably caused by differential preservation and/or differential archaeological recovery, and resulted from differences in the age structure, especially higher mortality rate amongst individuals older than 6 years in the MS group.