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

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

Czy zapory bobrowe w małych ciekach mają wpływ na efekty zarybiania trocią (Salmo trutta trutta)?

Wpływ zapór bobrowych na stan ichtiofauny cieków jest rozważany od wielu lat. Jedni autorzy twierdzą że zapory bobrowe odgrywają pozytywną rolę w funkcjonowaniu ekosystemów wodnych, ponieważ zwiększają bioróżnorodność ichtiofauny, podczas gdy inni twierdzą, że wpływ tych zapór jest negatywny. Celem pracy było określenie bezpośredniego i pośredniego wpływu piętrzeń bobrowych na liczebność ryb łososiowatych i skuteczność zarybiania nimi małych cieków Sitna i Pokrętna. W latach przed powstaniem zapory bobrowej narybek troci odławiany był na całej długości odcinka. Natomiast później, pomimo, że narybek wsiedlany był również powyżej spiętrzenia spowodowanego zaporą bobrową, to ryby w niewielkiej liczbie odławiane były tylko na odcinku poniżej spiętrzenia. Na podstawie wyników pracy można przypuszczać, że zapory bobrowe przyczyniły się do pogorszenia warunków biologicznych i morfologicznych, właściwych dla przeżycia ryb łososiowatych, jak również negatywnie wpłynęły na efekty zarybień. To negatywne oddziaływanie w największym stopniu widoczne było w przypadku liczby odłowionych ryb. Głównymi powodami spadku liczby odławianych ryb łososiowatych mogły być wywołane powstaniem zapory bobrowej: I) zmiany warunków hydrologicznych; II) zmiany warunków fizyko-chemicznych, szczególnie podwyższenie temperatury wody; III) zwiększenie liczby ryb typowych dla zbiorników limnetycznych, w tym szczupaka i okonia, drapieżników zjadających narybek troci; IV) zamulenie dna cieku

Genetic characterization of Atlantic sturgeon stocking material used in Lithuania to restore the Baltic Sea population

Background. Recent genetic analyses of fish remains, obtained from archaeological sites, revealed that more than 2000 years ago the Baltic Sea was inhabited by sturgeons closely related to the Atlantic sturgeon, Acipenser oxyrinchus Mitchill, 1815. As some wildlife populations of the Atlantic sturgeon are still present in Canadian rivers, we decided to use those fish to restore the extinct Baltic population. Materials and methods. Fin clips of 50 A. oxyrinchus were collected from fry representing two hatcheries. At the hatchery  No. 1 sturgeons were reared from fertilized eggs received from the Acadian Sturgeon and Caviar Inc., Canada. At the hatchery No. 2, larvae provided by the Regional Research Institute for Agriculture and Fisheries (Germany) were reared for several months until they were released into rivers. The molecular data of 22 and 28 specimens from hatcheries  No. 1 and No. 2, respectively, were compared with homological D-loop sequences and some microsatellite loci derived from two museum specimens of sturgeons from the Tadas Ivanauskas Museum of Zoology, Kaunas, Lithuania. Signs of possible introgressive hybridization between Acipenser sturio Linnaeus, 1758 and A. oxyrinchus in two museum specimens were checked by comparison of alleles at loci AoxD161, AoxD188, AoxD297, AoxD242, and AoxC30. A possible affinity of between sturgeons released in Lithuanian rivers in 2015 and samples representing hatcheries  No. 1 and No. 2 was estimated based on multi-locus genotyping data using the Structure software, version 2.3.4. Results. The same D-loop haplotype H1 characteristic for the museum specimens (MK637525 and MK637526) was also found as the only haplotype distributed among sturgeons reared in hatcheries and used for population re-establishment. A possible hybridisation between A. sturio and A. oxyrinchus was not confirmed for two museum specimens studied. The first results of genetic application undertaken in Lithuania also revealed the possibility to discriminate the individuals obtained from different hatcheries based on the set of 13 microsatellite loci Aox45, AoxD54, AoxD161, AoxD297, AoxD188, AoxD234, AoxD242, AoxC45, AoxC30, AoxD241, AoxD64, AoxD186, and Ls-68. The analysis of A. oxyrinchus specimens representing F1 generation of parental individuals reared in two separate hatcheries in Canada and Germany revealed significant differences in the allele composition and high probabilities for individuals released into the natural environment to be assigned to the hatchery of their origin. Conclusion. The results of the molecular analysis will be useful for identification of age, pedigree, and for initiating genetic monitoring of the restored population of the Atlantic sturgeon in the Baltic Sea