How long-term water level changes influence the spatial distribution of fish and other functional groups in a large shallow lake

We numerically explored the effects of long-term water level changes on biotic biomass and spatial distribution of fish in a large shallow lake. We calibrated Ecospace model (Ecopath with Ecosim modelling suite) with data from various functional groups (ranging from phytoplankton to piscivorous fish), and considered 14 different habitats. Two scenarios representing, respectively, a long-term water-level increase and decrease by 1 m were constructed and run for a period of thirty eight years (1979–2016). The results showed a very uneven spatial distribution of fish biomass in the lake, with the highest con- centration in the southern basin. The 1 m decrease scenario caused a diminution in the biomass of all groups but piscivorous fish. The 1 m increase scenario saw a weak decrease in most species biomass. Consequently, in both scenarios, long-term water level changes would be generally detrimental to the lake biota. In the context of more frequent climate-induced hydrological fluctuations, we encourage the use of these simulations as effective tools for future prediction and assessment of ecosystem-based fisheries management and ecological status maintenance of shallow lakes. This research was supported by Estonian Research Council grant PSG32 to FC and UB, by Environmental Investment Center project-T180209PKKH, by IUT 21-2 of the Estonian Ministry of Education and by European Union Regional Development Fund program DoRa+ and ASTRA. This research was supported by Estonian Research Council grant PSG32 to FC and UB, by Environmental Investment Center project-T180209PKKH, by IUT 21-2 of the Estonian Ministry of Education and by European Union Regional Development Fund program DoRa+ and ASTRA.