Does River Restoration Increase Fish Abundance and Survival or Concentrate Fish? The Effects of Project Scale, Location, and Fish Life History

Despite billions of dollars spent on various river restoration techniques, we still find ourselves debating whether habitat restoration increases fish abundance or concentrates fish. Based on the available literature, I discuss three important questions related specifically to the restoration of salmonid habitat: (1) “Does river restoration increase fish abundance or concentrate fish?”; (2) “Does river restoration increase fish survival or increase abundance?”; and (3) “Does the size or amount of river restoration influence fish response?” First, there is scant evidence to support the contention that river restoration leads to the concentration of fish at restoration projects. Second, the literature suggests that river restoration may lead to increased survival, increased abundance, or both. Third, recent studies have found little relationship between restoration project length and physical or biological response. The scientific literature does suggest that fish response to restoration varies greatly depending on the watershed template, location, and characteristics of the habitat restoration, and the life history of and limiting factors for a species. Thus, adequately determining whether changes in fish abundance observed in a restored area are due to increased movement, survival, or the amount of restoration will require detailed monitoring of these factors simultaneously.