Early life history dynamics and recruitment processes of rainbow smelt in Lake Huron

Rainbow smelt are an important prey species for native and introduced salmonines in the Great Lakes, as well as being a competitor and predator of native fish species. In Lake Huron, rainbow smelt populations have been characterized by variable recruitment and year class strength. To understand growth and survival dynamics during early life history, larval rainbow smelt populations were sampled during 2008 and 2009 in St. Martin Bay, Lake Huron. Growth rates of larval rainbow smelt and relative survival of stream cohorts was higher during 2009 than in 2008, a consequence of warmer water temperatures during June and cooler, more optimal temperatures during July. Early hatching stream cohorts experienced high mortality during 2008 and fish surviving experienced lower growth relative to cohorts during 2009. To investigate long term recruitment dynamics for these populations, Ricker stock-recruit models were developed for Lake Huron rainbow smelt sampled from 1976-2009. Ricker models were developed with the inclusion of four external variables that have been reported to affect rainbow smelt production: precipitation, water temperature, water levels, and lake trout abundance as measured by catch per unit effort (CPE). The best model describing rainbow smelt recruitment during 1976-2009 included lake trout CPE, Lake Huron water levels, and over basin precipitation. A separate model for the 1994-2009 time period identified lake trout CPE as an important regulator of rainbow smelt recruitment. These findings indicate that variability in growth and survival of rainbow smelt during early life history stages influences year class formation, but recruitment is strongly regulated by lake trout predation on adults or age-0 recruits.