Long-Term and Interannual Dynamics of Walleye and Yellow Perch in Saginaw Bay, Lake Huron

Walleye Sander vitreus and yellow perch Perca flavescens are well-studied, ecologically important fish species that co-occur in a wide range of systems and experience complex interactions; on the one hand, they are physiologically and ecologically similar and therefore may respond analogously to environmental variation, while on the other hand they interact antagonistically as competitors, predators, and prey. In Saginaw Bay, Lake Huron, walleyes and yellow perch have supported a combination of commercial and recreational fisheries and have been exposed to a series of ecosystem-level stressors and management actions that may have impacted these populations via multiple pathways. We used dynamic factor analysis and correlation analysis of walleye and yellow perch annual fall trawl catch data to elucidate the overall trends in walleye and yellow perch populations in Saginaw Bay. The results suggest that walleyes and yellow perch trend differently; while the relative abundance of age-0-2 walleyes generally increased and their mean length decreased from 1980 to 2008, the trends in yellow perch abundance and length differed among the young-of-year, yearling, and age-2 age-classes. Moreover, interannual negative associations between yellow perch relative abundance and mean size are suggestive of compensatory, density-dependent control on growth, while similar evidence is lacking for walleyes. Correlation analyses indicate that walleye year-class strength is set by the fall of age 0, while the age at which recruitment is set for yellow perch is less clear and may not occur until the fall of age 1. Thus, we suggest that future studies evaluating environmental determinants of year-class strength in Saginaw Bay evaluate age-0 walleyes and age-1 yellow perch. Finally, while age-0 yellow perch and age-0 walleyes appear to respond similarly to annual environmental conditions, the recent increase in walleye abundance and decrease in the mean size of age-0 yellow perch may have contributed to the reduced abundance of adult yellow perch via walleye predation and overwinter mortality.