Stranding potential of young fishes subjected to simulated vessel-induced drawdown

During early life stages, fish in the Mississippi River system may become s tranded by shoreline drawdowns induced by the passage of commercial vessels . We examined the stranding of larval shovelnose sturgeon Scaphirhynchus pl atorynchus, paddlefish Polyodon spathula, and bigmouth buffalo Ictiobus cyp rinellus and of juvenile blue catfish Ictalurus furcatus, largemouth bass M icropterus salmoides, and bluegill Lepomis macrochirus in a laboratory flum e. Stranding was measured at three vertical drawdown rates (0.76, 0.46, and 0.21 cm/s) and two bank slopes (1:5 and 1:10). Blue catfish, shovelnose st urgeon, and paddlefish were not tested at both bank slopes. Susceptibility to stranding varied among species and was independent of drawdown rate. At a slope of 1:5, shovelnose sturgeons had the highest stranding percentage ( 66.7%), followed by paddlefish (38.0%), bluegills (20.0%), bigmouth buffalo (2.2%), and largemouth bass (0.0%). At 1:10, blue catfish had the highest stranding percentage (26.7%), followed by largemouth bass (15.3%), bluegill s (5.3%), and bigmouth buffalo (0.0%). The likelihood of stranding was rela ted to the behavioral response of fishes to receding water levels. Species that typically occur in littoral and backwater areas swam with the current or passively drifted, whereas the young of main-channel fishes, such as stu rgeons and paddlefish, exhibited positive rheotaxis and were more likely to become stranded.