Overwinter survival of brook trout (Salvelinus fontinalis) from the 9-month-old fingerling stage to the 16-month-old yearling stage varied from 35 to 73% during 11 successive winters (1954–65). Mean survival through these first winters of life was 54%.Survival appeared to be independent of fingerling density most winters, and especially when September densities were less than 2200/km, as they were during 7 of 11 years. Overwinter survival tended to increase with an increase in mean length of fingerling stocks (r = 0.83++) and with an increase in winter water temperatures. Intraspecific predation did not appear to be a critical mortality factor. The survival advantage of increased fingerling size was probably related to increased physiological resistance to temperature-associated stresses rather than reduced vulnerability to predation.

Responses of a wild brook trout (Salvelinus fontinalis) population to instream habitat development in a 0.7 km reach of Lawrence Creek were monitored for 7 years and compared to population data for the 3‐year period prior to development. Mean annual biomass of trout, mean annual number of trout over 15 cm (legal size), and annual production increased significantly during the 3 years following development, but more impressive responses were observed during the second 3 years. Maximum number and biomass and number of legal trout did not occur until 5 years after completion of development. The peak number of brook trout over 20 cm was reached the sixth year after development. Where long‐term studies of aquatic systems are needed to evaluate effects of environmental perturbations, it may be desirable to deliberately delay collection of posttreatment data. Such a start‐pause‐finish sequence of research would provide more valid and less costly evaluations and utilize the time of researchers more efficiently.

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Objective: Bioprosthetic heart valves (BHVs) are commonly used in surgical and percutaneous valve replacement. The durability of percutaneous valve replacement is unknown, but surgical valves have been shown to require reintervention after 10 to 15 years. Further, smaller-diameter surgical BHVs generally experience higher rates of prosthesis-patient mismatch, which leads to higher rates of failure. Bioprosthetic aortic valves can flutter in systole, and fluttering is associated with fatigue and failure in flexible structures. The determinants of flutter in BHVs have not been well characterized, despite their potential to influence durability. Methods:We use an experimental pulse duplicator and a computational fluidstructure interaction model of this system to study the role of device geometry on BHV dynamics. The experimental system mimics physiological conditions, and the computational model enables precise control of leaflet biomechanics and flow conditions to isolate the effects of variations in BHV geometry on leaflet dynamics.

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