Reproductive Success of Northern Lake Trout Populations: The First Casualty of Climate Change?

Photoperiod is a primary and unambiguous cue for lake trout reproduction whereas temperature appears to be a secondary cue but one exhibiting considerable stochasticity. The extent to which these two factors interact to influence spawning period for this fall spawner is unclear but may be highly important for synchronizing the final stages of gonadal maturation and reproductive success. Climate change associated increases in lake temperature may result in delayed declines in temperature during the fall spawning period such that changes in temperature and photoperiod may become asynchronous. The influence of these changes on lake trout spawning period may be greater at high latitudes because of a greater rate of decline in photoperiod at high latitudes, likely increasing the influence of photoperiod as a reproductive cue. A meta-analysis of published and unpublished observations of lake trout spawning in North America revealed a decreasing ability of lake trout to adjust spawning date for interannual changes in temperature with increasing latitude. In addition there was much lower variation in spawning period for lake trout from high than mid latitude lakes where variation in spawning period appeared more strongly related to variation in temperature than photoperiod. The change in photoperiod one month prior to spawning was highly correlated with latitude, suggesting that with respect to spawning period, the relative influence of photoperiod likely increases while that of temperature decreases, with latitude. This was supported by observations of lake trout spawning in two northern lakes where despite markedly different cooling rates and temperatures at spawning, spawning periods were nearly identical. A marked difference in egg viability between the two lakes suggests that an inability to adjust spawning period for temperature increases predicted to accompany climate change may negatively affect recruitment.