Temperature Effects on Gizzard Shad Production in Two Missouri River Reservoirs: Another Result of the 2011 Flood

Water temperature plays a key role in triggering gizzard shad spawning activity and can also affect larval growth rates.   In 2011, the Missouri River basin had record runoff that resulted in flooding throughout the basin and record releases from upper reservoir controlled reaches.  High releases from main stem reservoirs resulted in lower water temperatures early in the year in Lake Sharpe and Lake Francis Case and likely influenced age-0 gizzard shad abundance, hatch timing, and larval growth.  We investigated this phenomenon by collecting larval trawl samples from Lakes Sharpe and Francis Case throughout the summer of 2011.  Additionally, we collected otoliths from larval gizzard shad to estimate hatch date and daily growth throughout the flood/cold water event.  Water temperatures reached 20^o C approximately 1 month later than average in Lake Francis Case and 1.5 months later than average in Lake Sharpe due to the high cold-water releases from Lake Oahe.  Peak distribution of gizzard shad occurred 43 days later in 2011 when compared to the 2004-2010 average for Lake Francis Case and 54 days later in Lake Sharpe.  Peak gizzard shad density was near average for Francis Case (16.7/100m³; 19.3/100m³ average), however, peak density in Lake Sharpe (6.3/100m³) was much lower than average (343/100m³).  These results indicate that cold-water flood releases from upper reservoirs influenced gizzard shad production in Lakes Francis Case and Sharpe in 2011.