Reproductive success of nase (Chondrostoma nasus L.) and its influence on population dynamics
Huber, M.; Kirchhofer, A.
Human habitat degradation can alter important factors for fish reproduction and survival of youngest life stages and therefore interfere with reproductive success. Although periodic species like nase (Chondrostoma nasus L.) can compensate for single years with unfavourable conditions for reproduction, an increase in numbers of years with unfavourable conditions for spawning could bring local subpopulations to extinction. If habitat fragmentation prevents recolonization, a massive regional population decline can be expected. In the present study, a simulation model including 4 different scenarios was used to explore the regulation of population development. Basic population parameters, survival of different stages of 0+ nase and reproduction were investigated on five different spawning grounds in the River Aare near Berne during three years. Missing data were obtained from the literature. Because of a high proportion of years with unfavourable conditions for reproduction of nase and an unbalanced population structure, a massive population decline has to be expected in the next years. Reproductive success, mortalities of early life stages and population structure are crucial for the population dynamics of the nase. Conclusions should be drawn for local habitat management. Small-scale habitat improvements promise best results to increase survival of 0+ stages. The protection of spawning sites and habitats with reduced currents for larval and juvenile nase under different discharge levels are proposed.