A major component of an Atlantic salmon population model developed by NMFS is the survival of smolts and kelts passing downstream at hydropower projects. To obtain this information, NMFS contracted Alden to estimate downstream passage survival of Atlantic salmon smolts and kelts at 15 hydroelectric projects on Maine’s Penobscot River and its tributaries. These desktop survival estimates focus on direct mortality attributable to passage at dams and to multiple dam passage. An established turbine blade strike probability and mortality model was used to estimate direct survival of fish passing through turbines at each project. Survival rates for fish that pass downstream over spillways or through fish bypass facilities were estimated based on existing site-specific data or from studies conducted at other hydro projects with the same or similar species. Most of the projects included in the study have upstream passage facilities for anadromous species (river herring, American shad, and/or Atlantic salmon), as well as operating downstream bypasses for juvenile and adult outmigrants. Some of the projects have installed narrow-spaced bar racks or overlays to reduce fish entrainment through turbines.
The results of Alden’s survival analysis provided data in a level of detail that would have been extremely expensive and difficult to accomplish with field studies. Typically, turbine passage survival studies conducted in the field only evaluate one or two turbines operating at one or two gate settings (i.e., flow rates). The methods and model developed for NMFS for Atlantic salmon on the Penobscot River are transferable to other river systems and species. The theoretical model for predicting strike probability is applicable to most species and the blade strike mortality data for rainbow trout are considered representative of many other species.