| Abstrakt: |
AbstractWe developed a bioenergetics model for steelhead Oncorhynchus mykissthat simulates growth and consumption by separate life history forms in Lakes Michigan and Ontario. We estimated abundances of hatchery and wild smolts during 1975–1990 for both lakes based on stocking rates, survival schedules, and discrimination of the proportion of the lake population that was naturally recruited. Recruitment of wild steelhead varied as a function of presmolt winter severity in both lakes. Wild smolts accounted for 6–44% (during 1982–1989) and 18–33% (during 1978–1985) of total annual smolt production in Lakes Michigan and Ontario, respectively. We developed an age-structured population model with separate accounting for run timing (summer, fall, and spring) using the proportions of life history stages observed at weirs and estimated adult survival rates. We summarized data on growth, diet, water temperature, and energy contents of predator and prey to model lakewide prey consumption in both lakes during 1975–1990. Lakewide prey consumption by steelhead amounted to 9,500 tonnes·year–1in 1987 in Lake Michigan and 2,200 tonnes·year–1in 1990 in Lake Ontario. Because of their limited dietary reliance on alewife Alosa pseudoharengusand rainbow smelt Osmerus mordaxand relatively low stocking density compared with other salmonines, steelhead consumed only 4% of available alewife production and 2% of total smelt production in 1987 in Lake Michigan. Although estimates of alewife production in Lake Ontario are presently unavailable, measures of alewife biomass in 1990 in Lake Ontario indicate that steelhead probably had a negligible effect on these prey fish. Steelhead consumed only 2% of total rainbow smelt production in Lake Ontario in 1990. Population biomass conversion efficiency (16.l%) and production-to-biomass ratio (mean, 1.18) for Lake Michigan steelhead are low compared with those of sympatric Oncorhynchusspecies. Sensitivity analysis of the population submodel indicated that the most sensitive parameters were lake survival and size at stocking. |
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