Technical Report

Swimming Performance of Rio Grande Silvery Minnow

URL: https://webapps.usgs.gov/mrgescp/documents/Bestgenetal_2003_SwimmingperformanceofRGSM..pdf

Date: 2003/05/01

Author(s): Bestgen K.R., Mefford B., Bundy J., Walford C., Compton B., Seal S., Sorensen T.

Publication: Final Report to U. S. Bureau of Reclamation, Albuquerque Area Office, New Mexico, 70 p.

Abstract:

The reach of the Rio Grande, New Mexico that supports remaining endangered Rio Grande silvery minnow Hybognathus amarus is dissected by numerous diversion dams that prevent upstream movement of fish. Upstream movement by adult silvery minnows is needed to offset downstream transport of semi-buoyant eggs and larvae following reproduction. Reestablishment of upstream colonization pathways for Rio Grande silvery minnow may require construction of artificial structures (fishways) for fish passage over low-head diversion dams in the middle Rio Grande. To assist with determining optimal passage designs, we assessed aspects of swimming performance and behavior of the Rio Grande silvery minnow in a variety of experimental settings. Results of experiments conducted showed that Rio Grande silvery minnow were capable and motivated swimmers. Rio Grande silvery minnow were capable of swimming at speeds up to 118 cm/sec for short periods of time in a swimming chamber at water temperatures of 15, 19, and 23 C. Swimming endurance increased as water velocity declined; a threshold for an exponential increase in swimming performance was noted at water velocities of 45 to 60 cm/sec. The threshold may represent a transition from anaerobic sprint swimming to more sustained aerobic swimming. Water temperature and fish length were positively correlated with swimming endurance. Rio Grande silvery minnow were also capable of long distance swimming over a relatively short time period; individuals routinely swam a static water distance equivalent of 50 km or more in less than 72 hr. Flume tests revealed that Rio Grande silvery minnow were capable of swimming over a variety of substrate particle sizes in a range of flow velocity conditions. Silvery minnow in the flume used velocity breaks behind cobble particles and the boundary layer to proceed upstream in an energetically efficient manner. We also measured passage rates of Rio Grande silvery minnows in four constructed fishways. We did not observe passage of silvery minnow released into Denil and single vertical slot fishways. High water velocities and complex, turbulent flow fields were the likely reason for passage failure. Up to 50% passage was observed in a dual vertical slot fishway at a relatively low water velocity; passage was only 8% at a higher velocity. Less turbulent flows were a likely reason for higher passage success compared to Denil and single vertical slot fishways. Wild and hatchery fish successfully ascended a rock channel fishway with a 1% hydraulic gradient. About 75% of all fish released passed the rock channel fishway in both low and high velocity flow conditions. Observations with underwater cameras and vertical velocity profiles suggested silvery minnow 8 used the lower velocity boundary layer and breaks adjacent to high flow zones to swim upstream. The mosaic of water velocities present in the rock channel fishway was likely the reason for relatively high passage success. We integrated time to fatigue relationships with hypothetical passage conditions such as fishway length and flow velocity, water temperature, and fish length, to determine design characteristics for structures. Recommendations made were based on functional swimming relationships and should assist managers tasked with design of structures appropriate for successful passage of Rio Grande silvery minnow. We also discuss uncertainties associated with fish use of the boundary layer, attraction flows, and interpretation of longer distance swimming ability. Because data gathered in this investigation address mostly design considerations related to swimming physiology of silvery minnow, the ultimate decision to construct a fishway should be based on a compendium of other supporting information.