Ekologiczny wpływ aktywności bobra europejskiego (Castor fiber) na populacje ryb w litewskich strumieniach pstrągowych

W artykule zanalizowano wpływ tam bobrów na różnorodność, liczebność, migrację i warunki tarliskowe ryb w potokach pstrągowych, które są licznie zamieszkiwane przez bobry. W zależności od rodzaju zapory i ich lokalizacji, strumienie zamieszkane przez bobry podlegają zmianom hydrologicznym, temperaturowym i chemicznym. Populacje ryb badano stosując elektro połów. Parametry populacji ryb (różnorodność gatunków, liczebność, biomasa) porównano w nienaruszonych przez bobry sekcjach strumieni i w sekcjach pod wpływem działalności bobrów. Ogólny stan ekologiczny strumieni oceniano stosując określone wskaźniki dotyczące ryb i wskaźniki zgodne z Ramową Dyrektywą Wodną. Przeprowadzone badania wykazały, że tamy bobrowe zmieniają skład populacji ryb, zmniejszają ich obszary produkcyjne i pogarszają warunki ów dla migracji rozrodczej pstrąga ora ogólny stan ekologiczny strumieni. Badania przeprowadzono w 2008 roku w 5 strumieniach pstrągowych - Dūkšta, Saria, Derežna, Agluona i Ežeruona zlokalizowanych w różnych częściach Litwy

Impact of the riverbed morphology on the source of organic material and the trophic structure of fish community along the upper reaches of the Nevežis River, Lithuania

Background. The catchment of the Nevežis River, the sixth longest river in Lithuania, is among the most affected by agricultural activities. Although seriously disturbed by land reclamation and agricultural pollution, the Nevežis River still has natural, anthropogenically unaffected stretches. Fish species were studied at two sites of the upper part of the river with different hydrological regime, exhibiting clear differences in the trophic status of fish. The combined effect of hydrogeomorphic and water-chemistry variability on the stable isotope composition of fish assemblages in Lithuania has not been investigated. The presently reported study was intended to explore the possible effects of the riverbed morphology and agricultural activities on the chemistry and stable isotope composition of the three main fish species. Materials and methods. This study covered three species of freshwater fishes: the European perch, Perca fluviatilis Linnaeus, 1758; the roach, Rutilus rutilus (Linnaeus, 1758); and the northern pike, Esox lucius Linnaeus, 1758. The sampling was performed in both natural and regulated river stretches using backpack electrofishing equipment. Stable isotope composition of the samples was revealed by applying stable isotope analyses (SIA) with an elemental analyser connected to an isotope ratio mass spectrometer. To obtain more information about environmental variability and variation of stable isotopes δ13C and δ15N in fish, the entire data matrix was analysed using Principal Component Analysis (PCA). Results. In the study sites on the Nevežis River, algal carbon isotope ratios were more 13C- depleted than those from terrestrial sources. The fishes were clearly dependent on terrestrial carbon sources in natural locations. However, the fishes collected from regulated sites had carbon isotope signatures more similar to algal than to terrestrial sources. Mean values of δ15N of the fishes from the natural sites were lower than those from the regulated ones. Conclusion. The presently reported study revealed impact of abiotic habitat variables indicating the importance of physicochemical and morphological characteristics on δ13C and δ15N isotopic values variance of fish at natural and regulated river sites. Our findings would help to evaluate and predict changes on river food webs that occur due to hydromorphological alterations determined by human activity and climate change. The results could be useful for fisheries, i.e., impact of environmental factors on fish nutrition and growth

Impact of the riverbed morphology on the source of organic material and the trophic structure of fish community along the upper reaches of the Nevežis River, Lithuania

Background. The catchment of the Nevežis River, the sixth longest river in Lithuania, is among the most affected by agricultural activities. Although seriously disturbed by land reclamation and agricultural pollution, the Nevežis River still has natural, anthropogenically unaffected stretches. Fish species were studied at two sites of the upper part of the river with different hydrological regime, exhibiting clear differences in the trophic status of fish. The combined effect of hydrogeomorphic and water-chemistry variability on the stable isotope composition of fish assemblages in Lithuania has not been investigated. The presently reported study was intended to explore the possible effects of the riverbed morphology and agricultural activities on the chemistry and stable isotope composition of the three main fish species. Materials and methods. This study covered three species of freshwater fishes: the European perch, Perca fluviatilis Linnaeus, 1758; the roach, Rutilus rutilus (Linnaeus, 1758); and the northern pike, Esox lucius Linnaeus, 1758. The sampling was performed in both natural and regulated river stretches using backpack electrofishing equipment. Stable isotope composition of the samples was revealed by applying stable isotope analyses (SIA) with an elemental analyser connected to an isotope ratio mass spectrometer. To obtain more information about environmental variability and variation of stable isotopes δ13C and δ15N in fish, the entire data matrix was analysed using Principal Component Analysis (PCA). Results. In the study sites on the Nevežis River, algal carbon isotope ratios were more 13C- depleted than those from terrestrial sources. The fishes were clearly dependent on terrestrial carbon sources in natural locations. However, the fishes collected from regulated sites had carbon isotope signatures more similar to algal than to terrestrial sources. Mean values of δ15N of the fishes from the natural sites were lower than those from the regulated ones. Conclusion. The presently reported study revealed impact of abiotic habitat variables indicating the importance of physicochemical and morphological characteristics on δ13C and δ15N isotopic values variance of fish at natural and regulated river sites. Our findings would help to evaluate and predict changes on river food webs that occur due to hydromorphological alterations determined by human activity and climate change. The results could be useful for fisheries, i.e., impact of environmental factors on fish nutrition and growth

Can the invasive New Zealand mud snail (Potamopyrgus antipodarum) threaten fisheries of temperate lakes? A case study from Lake Dusia, Lithuania

Background. To date, numerous studies of the impact of snail Potamopyrgus antipodarum (Gray, 1843) on invaded ecosystems have been conducted. However, the majority of such studies intended to assess changes induced in macroinvertebrate assemblages, while the possible effects of P. antipodarum on higher trophic levels have not hitherto been studied. Of particular interest from the point of view of fisheries management is the elucidation of how this invasive snail can alter the energy flow towards higher trophic levels. When abundant, P. antipodarum consumes a substantial part of the primary production, but it is poorly consumed by native fishes. Consequently, part of its assimilated energy may become locked in lower trophic levels and fail to reach higher levels directly. Therefore, invasion of this snail may decrease fish production. Materials and methods. Several years after establishment of P. antipodarum in a temperate mesotrophic Lake Dusia, we assessed: (1) changes in the biomass of littoral macroinvertebrates (proxy to secondary production), (2) assimilation of P. antipodarum by benthivorous fish (energy flow), and (3) changes in growth and catches of littoral benthivorous fish (fish production). All the analyses were based on a merger of “grey” literature and original data during the pre- and post-invasion periods. Results. There was an evident increase in the biomass of littoral macroinvertebrates, and the assemblage changed from crustacean- to gastropod-dominated due to over-domination of P. antipodarum. However, P. antipodarum did not replace the native prey of fish. Moreover, a marked decrease was recorded in littoral fish growth and catches after the invasion of P. antipodarum. Conclusion. Dense populations of P. antipodarum may reduce the channelling of primary production towards higher trophic levels and, consequently, the invasion may threaten fisheries of temperate mesotrophic lakes

Intestinal Parasites of Juvenile Salmonids from the Lower Oder River Basin and from the Middle of the Neman River

Atlantic salmon died out in Poland during the 1980s. The current population was recreated with Latvian salmon and now forms part of the southern Baltic cohort. Polish sea trout and brown trout come from the home cohort, but have survived only with regular restocking. In Lithuania, all the salmonides are from the home cohort and have not been restocked. The aim of this study was to compare parasitic invasion in juvenile salmonides that come from Poland and Lithuania. The juvenile salmonides in this study came from the lower Oder River basin and from the middle of the Neman River. 153 fish were caught using electrofishing from 2004 to 2006. The salmonides in the Oder had been artificially restocked and those in the Neman were wild. 33 salmon, 58 sea trout and 24 brown trout came from small tributaries of the Oder; 22 salmon, 5 sea trout and 11 brown trout came from tributaries of the middle Neman River. The fish were either 0+, 1+, or 2+ years old. Their size was characteristic for their species at that age, which suggested that they were in good condition. Our examination found 6 species of parasites from 3 taxa: Cestoda – Cyathocephalus truncates; Nematoda – Cystidicoloides ephe¬meridarum and Raphidascaris acus; and Acanthocephala – Acantho¬cephalus lucii, A. anguillae and Metechinorhynchus truttae. We found all three taxa of parasites in all the salmonides that came from the tributaries of the Oder, but all three taxa were found only in salmon from the Neman tributaries. In sea trout and brown trout from tributaries of the Nemen River we found only Nematoda. The invasion frequency was much higher in salmonides that came from tributaries of the Oder River than in salmonides from tributaries of the Nemen River. In tributaries of the Oder River, 57.6% of the salmon, 62.1% of the sea trout, and 58.3% of the brown trout had parasites. In tributaries of the Nemen River, 27.3% of the salmon, 40% of the sea trout, and 36.4% of the brown trout had parasites. In salmonides from both rivers the most common parasites were C. ephemeridarum, M. truttae, and C. truncatus. The other species of parasites were found in very few cases. Older salmonides had greater numbers of parasites. Although the salmonides came from different rivers and had different origins, the species of parasites that they had were typical for their family. In conclusion, parasite invasion is similar in salmonides both from the lower Oder River basin and from the middle of the Neman River