| Abstract [eng] |
Reproduction is a critical period of salmonid fish life history. As early life stages are particularly sensitive to biotic and abiotic constraints, studying these stages in terms of survival is essential in salmonid population ecology, stocks management, conservation and restoration. No characterization of salmonids spawning habitats on scientific basis has been made to date in Eastern Baltic region, which rivers are important for salmonid reproduction and significantly contribute to the sea trout and salmon stocks in the Baltic. The aim of this work was to assess sea trout spawning sites characteristics and to estimate its effects on reproductive success in a typical lowland salmonid stream – Blendžiava. The spawning site selection by sea trout females and characteristics of spawning sites at different spatial scales were determined, spawning nests sedimentary, hydraulic, and water physico-chemical characteristics were assessed. To test how the spawning site selection influence reproductive success, in situ experiment on survival of sea trout eggs, study on fry emergence from natural redds and on dispersal of juveniles after emergence were accomplished. Additionally, the study on reproductive interaction between sympatric lampreys and salmonids was conducted. Study results revealed, that sea trout has specific spawning site preferences at the stream-, reach- and microhabitat scale, and are related with optimal conditions for egg survival. Vertical hydraulic gradient of hyporheic flow was found to be essential factor, which determines spawning site selection at the microhabitat scale and affects intragravel physico-chemical conditions. Upwelling groundwater significantly negatively affects egg incubation efficiency and fry emergence. Detailed sea trout fry emergence study revealed specific fry emergence patterns and long period, which end is critical for body condition of emergent fish. Assessment of conditional status of salmonid fry at emergence was supported by novel approach based on analysis of muscle RNA:DNA ratio in emergent fry. Significant reproductive interaction in terms of sea trout redd superimposition by spring-spawning lampreys was described for the first time, suggesting likely ecological effect on pre-emergent and emerging trout fry. Results of present study supplement our understanding of complex ecology of early life stages of salmonids and ecosystems of salmonid rivers. |
