Fish spawning in a large temperate floodplain: the role of flooding and temperature

1. Floodplains are a key habitat for foraging, spawning and as a nursery for many riverine fish species. The lower Volga floodplains (Russian Federation) are still relatively undisturbed, while in Europe and North America, about 90% of floodplains have effectively been lost. 2. We examined relationships between the extent and timing of the spring flood, lateral spawning movements of fish species and timing and duration of spawning in the floodplain by sampling during spring 2006 and 2007. 3. Only the spawning of rheophilic species, that released their eggs in the floodplain, coincided with the flood. In contrast, the timing of spawning by eurytopic and limnophilic species was unrelated to flooding. 4. For most fish species, we found no indication that the majority of spawners in the floodplain originated from the main river channel, with the exception of sabrefish Pelecus cultratus. 5. We postulate that in the vast Volga-Akhtuba floodplain, fish spawning stocks mainly originate from permanent floodplain waterbodies, whereas hydrological conditions are dominated by the river. Both the river and waterbodies on the floodplain may serve as sources for recolonisation after local extinction because of extreme environmental conditions, such as freezing or desiccation.