Improving the reliability of fishway attraction and passage efficiency estimates to inform fishway engineering, science, and practice

Of late there have been several syntheses that consider the biological effectiveness of fishways. These syntheses emphasize the importance of generating estimates of attraction and passage efficiency, using electronic tagging techniques, as the “gold standard” for determining if a fishway is indeed successful at passing target species upstream to meet ecological, management, and conservation goals. Such an emphasis on efficiency is potentially problematic if estimates of attraction and passage efficiency are biased or otherwise fail to reliably represent the true biological effectiveness of a fishway. Indeed, erroneous estimates could lead to management decisions (in terms of both design criteria and operational decisions) that are costly in terms of economic expenditures and failed conservation outcomes for populations, species and ecosystems. Here we review the factors that are necessary to consider when determining the reliability of efficiency estimates for fishways and provide suggestions for improving such estimates. Clearly there is need for greater attention to the effects of various capture (including gear and the timing and location of capture), handling, and tagging protocols on fish necessary to monitor individual passage success given the potential for procedures to influence organismal condition and behavior. In addition, there is need for more long-term tagging studies (monitoring individuals across multiple seasons), mechanistic studies to understand the biological basis for differences in efficiency estimates, greater use of control studies to account for natural levels of migration failure/behavioral heterogeneity, technical validation of electronic tagging equipment (to account for tag failure and detection efficiency), and the use of approaches that combine individual monitoring with population-level studies (including modeling exercises). Also relevant is the need to better understand the proportion of fish that need to pass a fishway to address ecological, management and conservation targets, as well as identify the proportion of a population that is actually motivated to attempt passage in a given season. Failure to think critically about the factors for a given study/site that have the potential to influence estimates of passage and attraction efficiency will impede the ability of science and monitoring activities to inform fishway design and operation and ultimately improve aquatic ecosystems.