Estimates of egg deposition and effects of lake trout (Salvelinus namaycush) egg predators in three regions of the Great Lakes

Excessive mortality from spawning through the first year of life is likely responsible for recruitment failures in many lake trout (Salvelinus namaycush) populations. We evaluated relationships between interstitial predator species and lake trout egg deposition in three regions of the Great Lakes. The introduced crayfish Orconectes rusticus dominated the nearshore zone in northern Lake Michigan, whereas other sites in Lake Michigan and Parry Sound were dominated by native Orconectes propinquus. In Lake Champlain, sculpin (Cottus spp.) were the most common interstitial predator, yet densities were comparable with those in Lake Michigan. Predator densities in Lake Michigan (mean +/- standard error = 15.5 +/- 0.4 predators center dot m(-2)) were twice those in Lake Champlain or Parry Sound (6 +/- 1 predators center dot m(-2)). Densities of eggs were higher in Lake Champlain (2994.1 +/- 398.3 eggs center dot m(-2)) and Parry Sound (454.7 +/- 36.3) than in Lake Michigan (7.5 +/- 1.3; Kruskal-Wallis, P <= 0.05). Ratios of eggs to predator provide simple measures of the effectiveness of lake trout rehabilitation efforts. The average ratio calculated from 10 successful spawning locations is 190 eggs center dot predator(-1 center dot)m(-2). Ratios may help establish target egg densities for restoration efforts and the concentration of spawning adults required to allow survival to the fry stage.