Does spatial variation in egg thiamine and fatty‐acid concentration of Lake Michigan lake trout Salvelinus namaycush lead to differential early mortality syndrome and yolk oedema mortality in offspring?

Individual variation in fatty‐acid and thiamine concentrations were determined in lake trout Salvelinus namaycush eggs collected at two spawning grounds in Lake Michigan. A suite of predictor variables, including spawning location, egg fatty‐acid and thiamine concentrations, were used to attempt to explain cause‐and‐effect in early life stage mortality among S. namaycush families. Lipid and fatty‐acid composition of S. namaycush eggs differed between spawning locations. Salvelinus namaycush offspring from south‐western Lake Michigan were affected by a high occurrence of yolk oedema, whereas a higher frequency of early mortality syndrome (EMS) was observed among offspring from the north‐western part of the lake. Random‐forest regressions revealed location as the most influential predictor of yolk oedema mortality, whereas thiamine level in eggs was the strongest predictor of EMS‐related mortality. Several polyunsaturated fatty acids were also found to be predictors of both mortalities. There is evidence of spatial variability in egg fatty‐acid concentration among S. namaycush in Lake Michigan that, together with diminished thiamine concentration, contribute to low survival of S. namaycush progeny.