Effects of Seasonal Flooding on Fish

By Damon Mullis, Research Scientist

Katie with Carp
Research Scientist Katie Johnson processes a large carp collected during a fish sampling event in April 2016 after flood waters recede.

This past fall and winter, the Savannah River experienced unusually high water levels. Although flooding can have negative impacts in the form of property and infrastructure damage, it can have many benefits. Floods are normal occurrences that fill natural depressions, reservoirs, irrigation canals, and help recharge ground water supplies, which all are important sources of drinking water or essential for agriculture.  This periodic inundation of the floodplain is critical for the maintenance of the river’s ecological, geomorphological, and hydrological integrity. This interaction between the river and its floodplain is believed to be a major driving force for the maintenance of biotic diversity and the production of plant and animal biomass, including fish. This suggests that the floodplain provides an abundance of food for riverine fish and increases overall production. Many fishermen have observed this relationship, catching larger fish after flooding events.

Flooded Boat Landing at Oxbow
December 29th 2015- Flooded boat landing and parking area at Savannah River Oxbow (Miller Lake, Tuckahoe WMA)

In addition, high flows allow fish access to floodplain environments which are believed to be ideal spawning habitats for some species. It seems the timing of periodic flooding is also important for successful fish recruitment, with good recruitment occurring in situations when the rise in water level and temperature are coupled, and conversely, poor recruitment occurring if seasonal flooding does not occur or retreats too quickly during the spring.  This relationship suggest that flooding enhances recruitment by directly stimulating spawning and/or providing adequate spawning habitat, and indirectly by enhancing larval and juvenile survival by providing abundant food and habitats on the inundated floodplain. Since this recent flooding event occurred during our ongoing Savannah River Oxbow research project (http://phinizycenter.org/phinizy-researchers-to-study-savannah-river-oxbow-lakes/), we will be able to explore the effects of flooding on the fish in these lakes as well as many other communities and ecological processes.