Aquatic Organism Passage and Road-Stream Crossings: Synthesis and Guidelines for Development of Effectiveness Monitoring

Restoration of passage for fish and other aquatic organisms at stream-road crossings represents a major investment.  Whereas restoring connectivity where it is impaired seems to be an obvious need, the benefits are not always clear.  The benefits of passage restoration should depend on the mode and extent of movement exhibited by potentially impacted species, and whether or not species require habitats isolated by barriers.  Increasingly, threats posed by invasive species have complicated decisions about passage restoration. Restoration of passage should therefore have somewhat predictable consequences, based on these species characteristics.  Recently there have been calls for increased effectiveness monitoring of aquatic organism passage restoration, and a workshop was held in March 2010 to discuss the merits of four approaches: individual movement, abundance, molecular genetic markers, and occupancy models.  We discuss merits and limitations of each of these methods in relation to the diverse species, natural settings where passage is restored, study designs, and logistical considerations.  Together these considerations can be applied to develop a set of guidelines for monitoring the effectiveness of passage restoration for aquatic organisms.