Movement and Survival of Stream Fishes During Periods of Low Flow

Only ecological-relevant instream flows will adequately protect lotic biota from the extreme consequence of flow alterations.  By linking flows to key biological processes, managers can identify actual environmental thresholds for target species.  Connectivity is a good example where loss of functional connectivity occurs at a discharge above where structural connectivity is lost.  We conducted a community wide mark-recapture study to evaluate the consequences of lowered discharge on channel-unit connectivity and survival of fishes.  Transition probabilities and survival estimates were calculated in Program MARK from the recapture of passive-integrated-transponder (PIT) tagged fishes (n = 419).  From June to November 2012, 60% (n = 253) of PIT-tagged fish were recaptured and 29% (n = 73) of recaptures indicated movements between channel-unit types.  Species that moved most often included: cardinal shiner Luxilus cardinalis, central stoneroller Campostoma anommalum, northern studfish Fundulus catenatus, redspot chub Nacomis asper, and juvenile smallmouth bass Micropterus dolomieu.  These data were used to develop survival thresholds relative to habitat connectivity to guide minimum-flow standards as a management option.