Pozorování hejnového chování ryb v pelagickém habitatu umělé vodní nádrže prostřednictvím videokamery

HOLUBOVÁ, Michaela

The research presented in this thesis contributes to broadening of the knowledge on free-living adult fish schools and behavioural patterns in a temperate freshwater reservoir. The behaviour of fish in the pelagic zone is rather poorly studied. Naturally, schooling tendency varied between species mostly due to increasing vulnerability to predation. Heterospecificity in schools was not a rare phenomenon, mainly for vulnerable species that shared the same space and food niche with a predatory less attractive species. The individual needs fluctuate as factors might be reconsidered in short time periods and most probably are reflected in behavioural responses. Individual responses are also reflected in the distribution of the fish in the reservoir and density in particular habitat. There is a "critical density" that triggers the formation of fish schools, followed by a slowing increase in density of fish clusters (observed units). This corresponds to increasing proportion of fish in a school and declining proportion of singletons. The trend of count of clusters tended to have an upper limit that should result in constant count of fish clusters after reaching a particular fish density. In other words, fish in the habitat maintain maximal distances even when the density increases. During high density periods the distances are kept by school formation. Overall the usage of the visual census as presented, proved to be a convenient tool for observation and assessment of freshwater fish. It has been demonstrated that the method can obtain comparable results to hydroacoustic survey amounts as well as purse seining.

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