A Half-Century of Walleye Research on Oneida Lake, New York: From Confidence to Confusion in the Face of Exotic Species

Oneida Lake, New York, is the State’s second most heavily fished body of water, receiving some 300,000 angler-hours of effort annually.  Walleye account for 60-80% of the targeted effort on the lake and harvest rates typically run over 90% of the legal-sized catch.  With support of the New York State Department of Environmental Conservation, the Cornell Biological Field Station has monitored walleye population dynamics for 55 years.  Through the 1980s, the adult walleye population fluctuated between 500,000 and 900,000 fish, and was tightly linked to yellow perch dynamics.  Both angler catch rates and survival of young walleye were linked to abundance of young yellow perch, serving to stabilize the predator-prey dynamics of the lake.  Beginning in the 1980s, a series of perturbations disrupted the dynamics of the system.  In the late 1980s, white perch and gizzard shad, previously present at low levels, began to increase in abundance.  In the early 1990s, zebra mussels colonized the lake and a breeding colony of double-crested cormorants established one of the lake’s islands.  Significant increases in water clarity associated with the establishment of zebra mussels led to increased mortality rates of larval walleye and yellow perch, likely contributed to by increased abundance of white perch.  Predation by double-crested cormorants reduced survival of sub-adult walleye and yellow perch.  By the late 1990s, the adult walleye population had declined to 200,000 fish and the adult yellow perch population declined by more than 50%, to just below a million fish.  An intensive cormorant management program initiated in the early 2000s, combined with more restrictive harvest regulations, allowed walleye numbers to almost double from the lows of the late 1990s, but yellow perch numbers remained well below historic levels.  Early life stage mortality for both species remains high, and most signs indicate that both walleye and yellow perch populations have reset at levels approximately 50% of their historic abundances.  The predator-prey dynamics between walleye and yellow perch are no longer the driving force behind recruitment variability and large year classes that traditionally support the walleye fishery are much less frequent.  While current levels of recruitment and harvest appear sustainable, the walleye fishery now appears to be more vulnerable to overharvest.  The combined impacts of multiple invaders has disrupted an historically stable fishery and reduced the ability to accurately forecast population numbers in order to manage proactively.