We conducted studies in the laboratory, experimental ponds (0.8 and 2.0 hectares), and small impoundments (69 and 253 hectares) to define temporal patterns of tiger muskellunge mortality and to identify factors controlling their mortality and growth. Total mortality 50 days after stocking in ponds or impoundments ranged from 5 to 100% and averaged about 70% in sixteen trials. Mortality of hybrids due to stresses associated with transport, handling and temperature changes at stocking were reduced when fish were stocked in early autumn at water temperatures below 20°C. Mortality attributable to predation by largemouth bass ranged from 0-100% (mean 30%) and was related directly to largemouth bass densities and inversely to indices of abundance of largemouth bass prey. Predation on hybrids was most intense when small fish (168-184 mm long) were stocked in summer and was inconsequential when large hybrids (196-255 mm long) were stocked in autumn. The presence of aquatic macrophytes did not influence intensity of predation by moderate to high densities of largemouth bass, even though hybrids preferred vegetated areas/
Overwinter survival of hybrids was directly related to their length. Largest hybrids (mean length 255 mm) had highest survival to spring (at least 40%) and to the following autumn (13%). Hybrid diet was related to prey type, density and size. When gizzard shad were present they were the most common prey and growth of hybrids was faster in lakes with a gizzard shad-cyprinid forage base than in lakes with only centrarchids. Because hybrid growth was positively related to prey density and hybrid size was directly related to survival, an assessment of available forage should provide guidance on number and size of hybrids to stock in a given lake. By stocking relatively large hybrids in autumn, short term survival can be enhanced. However, factors affecting overwinter survival need to be identified before appropriate measures can be develop to increase survival to age 1.