Adrift at "sea": Episodes and pitfalls associated with survival of marine and freshwater fish larvae

Background/Question/Methods The processes that affect year-class strength in freshwater fishes are typically considered to be much different than those that determine year-class strength in marine fishes. Because early life stages of freshwater fishes are considered to have a short pelagic phase, processes that affect recruitment are typically thought to occur during the larger juvenile stages. Year-class strength of marine fishes is often set early during the larval stage, where starvation and physical factors frequently affect survival. Yet, freshwater species in large lakes such as the Laurentian Great Lakes, can experience an early life history similar to that seen in many marine species. As a result, it may be instructive to compare the patterns affecting year-class strength in large freshwater systems to those of marine environments. In the Great Lakes, many fishes have early life stages with pelagic larvae. We argue that year-class strength of freshwater fishes experiencing extended pelagic stages will be mediated by similar factors to those that structure recruitment in marine systems. 

Results/Conclusions As an example, age-0 yellow perch (Perca flavescens) and other species with pelagic early life stages in Lake Michigan spend at least 60 days in the pelagia, where they drift with the prevailing currents.  During this period, both physical processes and starvation structure mortality of weekly cohorts of age-0 fish.  By the time age-0 yellow perch return to demersal, nearshore nursery areas, year-class strength appears to be set.  We believe that fish with long pelagic early life stages that reside in large systems are subject to similar processes that govern recruitment success. As a result, the size of the water body and the amount of time spent in the pelagia during early life may be more important determinants of year-class strength of fishes than is the amount of sodium chloride in the water.