Ichthyocenosis of the Podolský Brook spring section in the Hrubý Jeseník mountains (Upper River Odra basin) within the context of the presence of fish predators

The study summarises results of the ichthyologic research of the Podolský and Stříbrný brooks in Hrubý Jeseník. The research was organised for the purpose of finding the actual situation in the fish settlements in the sections of interest and to make suggestions for their further management benefiting the original fish communities. The results have shown that there is the community of water organisms with naturally reproducing Cottus poecilopus and Salmo trutta in both partly adjusted water flows which have not been restocked by man since 1996. The facts found within the research suggest that the biologically correct way for the further development of fish populations in the Podolský and Stříbrný brooks may be the maintenance of the existing natural conditions while no local adjustments of the flow beds along roads should be excluded. The research results have proved that the existing natural conditions and the very limited anthropogenic pressure put on the water biocenoses have been the decisive factors during the formation of the now existing fish population structures which can be assessed as good from the ecological point of view. Because of that we have recommended to the manager of the water flows neither interfering in the development of the current fish populations nor restocking any fishes. We consider the finding that the age structure and the high numbers of Salmo trutta and Cottus poecilopus have been, in the given situations, the indicators of their populations’ ability, even at the sympatric presence of Lutra lutra and Ciconia nigra, resistant against the predators’ pressure, as very important.

Vertical Distribution of Cottus poecilopus Heckel, 1837 in Streams of Tatra National Park in Poland

The aim of the study was to determine the prevalence of Cottus poecilopus in the main streams of the Tatra National Park in Poland. Fishing research was conducted within the summer and in the autumn of 2014 for fourteen streams. The catches were made with pulse fishing device (IUP-24) wading up stream. During fishing caught fishes have been characterized and habitat has been characterized by noting the speed of the current, the presence of obstacles and hiding places for fish, width, type and size of the bottom substrate, the presence of wood and shade. The beginning and end of each transect was described by the geographic coordinates using a Garmin GPS device. Based on the geographical coordinates the project was created in GIS (using ArcMap software 9.3.1) and determined the amount of occurrence of fish above sea level. In the course of fishing three species of fish were found: Cottus poecilopus, Salmo trutta m. fario and Salvelinus fontinalis. In the studied streams Cottus gobio was not found. The most numerous Cottus poecilopus were represented, a total of 485 individuals in 12 streams. Stream Chochołowski Potok (1077.3 m above sea level) was the highest position where the genre occured.

Beaver impact on stream fish life histories: the role of landscape and local attributes

The Eurasian beaver (Castor fiber) has been reintroduced into the Carpathian Mountains and has once again become an important factor for modifying streams. Forty-three sampling sites were compared with 10 reference sites in streams not settled by beavers. Models related to the impacts of beavers on various fish life history stages and a model presenting attributes influencing the ichthyofauna structure in streams with and without beavers were generated. Significant differences in the fish species composition were found between beaver ponds versus the running sections of streams. The changes associated with pond aging caused decrease of Siberian bullhead (Cottus poecilopus) density. For brown trout (Salmo trutta), beaver ponds were the only location where large individuals were found, while the upstream parts of the beaver complexes provided spawning habitat and an area for fry growth. Common minnow (Phoxinus phoxinus) and stone loach (Barbatula barbatula) had higher density in ponds than in streams. The decisive factors for the ichthyofauna in the mountain streams settled by beavers were local attributes related to beaver activity. Our results illustrate interactions among beaver, landscape context, and fish life history in influencing the response of the stream fish assemblages to beaver recolonization. It also helps answer the question of how Eurasian beaver influence stream fish assemblages, at a much larger scale than previous studies.