Organism Movement–Fish

For fish, swimming ability is highly variable among species. While terms related to swimming ability do not have standardized meaning, most researchers use three categories to describe swimming ability. These include, burst speed (relatively high speeds that can be maintain for only a few seconds), prolonged swimming speed (includes the range of speeds between burst and sustained), and sustained speed (speeds that can be maintained for long periods without fatigue). Swimming speeds are significant factors when one considers the ability of animals to move through river and stream ecosystems. Burst speed is most relevant for physical barriers or short sections of relatively high water velocity. Prolonged speed is important for crossing longer sections of high water velocity. Long-distance movements of migratory fish and the ability of fish to maintain position in the stream channel for long periods of time depend on the sustained speed of fish.

The danger in using data on the swimming abilities of fish to design river and stream crossings is that we have the most information about strong swimmers (migratory fish) and know very little about the majority of fish species, especially small fish (including juveniles). We know even less about the swimming abilities of non-fish species that inhabit rivers and streams. Species-specific design is also hampered by a lack of information about how turbulence affects animal passage. Theoretically we can reduce velocities within the crossing structure by increasing roughness, such as through the use of baffles. However, increasing roughness also increases turbulence and we have very little information about the ability of various organisms to move through areas of high turbulence.