GALCIT Colloquium

Fishes experience a wide range of velocity variation and vorticity in their natural habitats. Current research shows that response times to disturbances are sufficiently long that powered corrections of resulting disturbances risk "pilot-induced error". Therefore, the ability to stabilize posture and trajectories should be important in habitat choice. To better understand the relationship between habitat choice and fish responses to flow induced perturbations, experiments were performed in three types of environments: a wave-dominated lakeshore, a trout stream and the laboratory. Results are presented for all three situations. For the lakeshore experiment, three fish species (bluegill, yellow perch and spottail shiner) were tested. The velocity was quantified in three directions using an Acoustic Doppler Velocimeter (ADV). The fish responses to wave induced turbulence were documented in terms of roll and surge motions. Significant differences in behavior were observed among the three species in the study. For the trout stream experiment, observations were made on current speeds and turbulence intensity (TI) using an ADV. Exemplary transects showed current speeds ranged from 0 to 60 cm/s and TI ranged from 0 to 0.7. TI was inversely related to current speed. Brown trout were usually found in the lower 5 cm of the stream where shear forces result in high turbulence. Locations occupied by brown trout had lower TI than similar situations lacking trout and yet higher TI than typical of the average stream. In the case of the laboratory experiments, different geometries are tested for a wide range of Reynolds numbers. Fish (Creekchub) responses are quantified in terms of critical swimming speed, fish trajectory and fin usage.