Influence of water temperature on rainbow smelt spawning and early life history dynamics in St. Martin Bay, Lake Huron

Rainbow smelt are an important prey species for native and introduced salmonines in the Great Lakes. In Lake Huron, rainbow smelt populations are characterized by variable recruitment and year-class strength. To understand the influence of water temperature on reproduction, growth, and survival during larval-fish stages, we sampled spawning tributaries and larval-fish habitats during 2008 and 2009 in St. Martin Bay, Lake Huron. Spawning by rainbow smelt occurred primarily when stream temperatures were between 3 and 10 °C, which resulted in a 7–10-day spawning period during 2008, and a 15–20-day spawning period during 2009. Regardless of these differences in spawning temperatures and duration, peak larval-fish densities during 2008 were double those observed during 2009. Length–frequency analysis of larval-fish populations during both years revealed stream-hatched fish during May and a later emergence of larval rainbow smelt during summer, presumably originating from lake spawning. Warmer bay water temperatures led to earlier emergence of lake-spawned rainbow smelt larvae during 2009. Stream-hatched fish larvae experienced large-scale mortality during May 2008 resulting in a bay population consisting primarily of lake-spawned rainbow smelt larvae, but during 2009 both stream- and lake-hatched cohorts experienced higher survival concomitant with significantly higher mean population growth rates. Higher larval-fish growth rates during 2009 appeared to be density-dependent and facilitated by warmer water temperatures during late June and cooler water temperatures during July. Temperature-mediated differences in annual growth rates and irregular contributions from stream- and lake-hatched fish larvae are important factors affecting survival and abundance of young-of-the-year rainbow smelt in Lake Huron.