Predation on lake trout eggs and fry: a modeling approach

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush, associated with spawning reefs. Three kinds of predation were simulated: epibenthic e gg predators consuming eggs on the substrate surface during spawning, inter stitial egg predators that can move in rocky substrate and consume incubati ng eggs, and fry predators. Also simulated was the effect of water temperat ure on predation rates. The model predicted that interstitial predation on eggs accounted for most (76 to 81%) of the predation on early life history stages of lake trout; epibenthic egg predation (12 to 19%) and fry predatio n (0 to 12%) had less effect on lake trout survival. Initial predation cond itions chosen for the model were: epibenthic egg predation peaked at 2 eggs /m(2)/d over 30 d, interstitial egg predation at 2 eggs/m(2)/d over 180 d, and fry predation at 1 fry/m(2)/d over 60 d. With a starting egg density of 100 eggs/m(2) and initial predation conditions, no lake trout were estimat ed to survive to swim-up. At egg densities of 250 eggs/m(2), 36% of the lak e trout survived. At the highest egg densities examined 500 to 1,000 eggs/m (2), estimated survival increased to about 70 to 80%. Simulated survival ra tes of lake trout decreased dramatically as predation rate increased but we re not as sensitive to increases in the duration of predation.