Dynamic Influences of Environment and Stock Size On Recruitment of Rainbow Smelt in Lake Michigan

Rainbow smelt Osmerus mordax represent an important prey for several recreationally valuable piscivores in the Great Lakes and support locally important fisheries throughout the region.  However, rainbow smelt populations have suffered steep declines in abundance over the past two decades, which may be associated with prolonged poor recruitment success.  The objective of this study was to evaluate the importance of environmental variables, such as salmonid predator abundance, lake level, and spring precipitation, in structuring recruitment of young-of-the-year rainbow smelt in Lake Michigan.  To do so, we examined the rainbow smelt stock-recruitment relationship derived from annual fall bottom-trawl surveys carried out by the U.S. Geological Survey from 1973-2012.  Because rainbow smelt growth and length at maturity declined over time, we determined stock biomass by estimating annual length at first maturation from maximum observed lengths, and recruit abundance through assessment of length frequency histograms.  We used a hierarchical stock-recruitment model to assess how stock size and environmental variables have influenced recruitment through time.  By evaluating important drivers of a relatively understudied process in rainbow smelt, we provide useful information for biologists seeking to understand the implications of future environmental change on the population dynamics of this important forage species.