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Diet-related thiamine deficiency increases the acute mortality, known as early mortality syndrome, of salmonines from some of the Great Lakes. The consequences of thiamine deficiency as measured at the egg stage for other important early life stage processes like growth, foraging efficiency, and predator avoidance that may also result in mortality, are unknown. Accordingly, we investigated the impacts of low thiamine on the specific growth rate (SGR) of first-feeding fry, the ability of first-feeding fry to capture Daphnia, fry emergence in the presence of a potential predator (round goby Apollina [formerly Neogobius] melanostomus), and predation by slimy sculpin Cottus cognatus. We used a combination of thiamine-deficient and thiamine-replete wild stocks of lake trout Salvelinus namaycush for this purpose. From these investigations we developed predictive relationships. Specific growth rate was related to egg thiamine concentration. From the exponential relationship, it was predicted that the threshold egg thiamine concentrations associated with 20% and 50% reductions in SGR are 8.1 and 5.1 nmol/g, respectively. The foraging rate on Daphnia was also related to egg thiamine concentration by an exponential relationship. It was predicted that the threshold concentrations associated with 20% and 50% reductions in this rate are 6.9 and 2.9 nmol/g, respectively. The presence of a round goby significantly reduced emergence success, but the level of goby predation was unrelated to egg thiamine concentration. Sculpin predation was related, although weakly, to the initial egg thiamine concentration. This research found that thiamine deficiency affected growth, foraging, and predator avoidance in lake trout fry. Growth effects resulting from thiamine deficiency may represent the most sensitive means of monitoring the impact of the secondary consequences of thiamine deficiency. Mortality associated with the combined effects of reduced growth and foraging has the potential to seriously impair lake trout recruitment.

The influence of egg predators and physical disturbance on lake trout Salvelinus namaycush egg mortality was investigated in situ in Lake Michigan where recruitment is below detectable levels and egg predator abundance is high. Comparisons were made with Lake Champlain where recruitment is low and egg predator abundance is also low and with Parry Sound (Lake Huron) where recruitment is moderate and egg predators are in low abundance. A multi-density egg seeding method (100 to 5000 eggs m À2 ) was used to quantify the effect of physical disturbance and egg predation on egg loss. Wind fetch was used as an index of physical disturbance and comparisons across all locations and egg densities suggested that at sites with high wind fetch (>5 km), physical disturbance may be a greater source of egg loss than predation. When analyses were limited to those sites having a wind fetch of <5 km, the percentage of eggs recovered was found to be linearly related to predator density. The strength of this relationship was based largely on egg recovery at 500 and 1000 eggs m À2 because recovery at lower (100, 250 eggs m À2 ) and very high (5000 eggs m À2 ) densities was not significantly related to predator density. The reason for this is probably that at low egg densities, crayfish Orconectes spp., the major egg predator at most sites, had difficulty finding and consuming eggs and at high egg densities they became satiated. Egg loss was directly related to wind fetch for Lake Michigan and on average six-fold greater than for Parry Sound suggesting that without corresponding changes in fecundity and age structure, lake trout populations in large lakes like Lake Michigan are inherently less productive than those from enclosed inland waters.