Mechanisms Driving Recruitment Variability in Fishes: Comparisons Between the Laurentian Great Lakes and Marine Systems

In his seminal work, Hjort (1914) observed that fish population levels fluctuated widely, year-class strength was set early in life, and egg production by adults alone could not explain variability in year-class strength. These observations laid the foundation for hypotheses on mechanisms driving recruitment variability in marine systems. We conducted a literature review to determine factors driving recruitment in Great Lakes fishes. We found that temperature, interspecific interactions, and spawner effects (abundance, age, and condition of adults), were the most important factors in explaining recruitment variability in Great Lakes fishes, whereas relatively few studies identified bottom-up trophodynamic factors or hydrodynamic factors as important. Next, we compared recruitment between Great Lakes and Baltic Sea fish populations and found no statistical difference in factors driving recruitment between the two systems, indicating that recruitment hypotheses may often be transferable between Great Lakes and marine systems. Because the Great Lakes are smaller and more enclosed than marine systems, and have abundant fishery-independent data, the Great Lakes are excellent candidates for future hypothesis testing on recruitment in fishes. We suggest that the Great Lakes may be particularly useful for understanding the effects of climate change and invasive species on fish recruitment.