Improved understanding of the causes and consequences of recruitment variability can help sustain fish populations and the fisheries they support effectively.
Recruitment—the process by which new members are added to a population through maturation—governs the status and trajectory of fisheries. Comparing how recruitment dynamics vary among populations, species, and over time can elucidate the biological and physical drivers of recruitment. For example, recruitment synchrony, where the recruitment of distinct populations or species is correlated, can suggest that similar processes regulate recruitment.
The Laurentian Great Lakes of North America form the largest freshwater ecosystem on Earth, analogous to inland seas, and support extensive fisheries. Lake Whitefish (Coregonus clupeaformis) and Cisco (C. artedi) are two closely related species that are ecologically, economically, and culturally significant across the Great Lakes region. Unfortunately, many populations have experienced poor recruitment in recent decades, though the nature of these declines varies between species and among populations. While the five Great Lakes share many characteristics (e.g., climate, biogeography), biophysical conditions such as food web structure can differ substantially. Comparing recruitment dynamics between species and among lakes can help clarify the causes of recent trends and inform management strategies under varying ecosystem conditions.
In this Editor's Choice article, the authors characterized over half a century of Lake Whitefish and Cisco recruitment variability in each of the Great Lakes and Lake Simcoe, another large lake within the Great Lakes region. They integrated catch and age data from 38 long-term surveys spanning 1960–2019. Using these data, they estimated year-class strength—a key measure of recruitment—for both species in each lake and tested for synchrony in year-class strength between species, among lakes, and through time.
The study revealed fundamental differences in recruitment dynamics between Lake Whitefish and Cisco. Year-class strength was not synchronous between the two species within any of the study lakes, suggesting that different biophysical processes regulate recruitment. The degree of recruitment synchrony among lakes also differed between species, highlighting the varying importance of regional versus local processes for each species. Lastly, the authors identified species-specific patterns of year-class periodicity, offering insights into how often strong year-classes may occur for each species.
This study enhances our understanding of Lake Whitefish and Cisco recruitment dynamics, supports ongoing management and stewardship efforts, and provides a foundation for future research on the biophysical drivers of recruitment variability.
Read the full paper, Reconstructing half a century of coregonine recruitment reveals species-specific dynamics and synchrony across the Laurentian Great Lakes, in ICES Journal of Marine Science.
