Oneida Lake: Long-term Dynamics of a Managed Ecosystem and Its Fishery

Chapter 19: Evaluating the Influence of Double-crested Cormorants on Walleye and Yellow Perch Populations in Oneida Lake, New York

Jeremy T. H. Coleman, Robin L. DeBruyne, Lars G. Rudstam, James R. Jackson, Anthony J. VanDeValk, Thomas E. Brooking, Connie M. Adams, and Milo E. Richmond

doi: https://doi.org/10.47886/9781934874431.ch19

Top predators are known to impact community structure in aquatic systems (Carpenter et al. 1985; McQueen et al. 1989), but establishing causality behind observed population-level changes can be difficult, especially in large, complex systems. Steady increases in cormorant populations during the 1980s and 1990s caused concern about the detrimental impact of the resulting predation on economically important wild fish stocks in both North America and Europe (see edited volumes by Nettleship and Duffy 1995; Cowx 2003; van Eerden et al. 2011). However, a definitive understanding of the nature of cormorant impacts on valued fish populations has been elusive due to the complexity of aquatic food-webs, the diversity of species assemblages in study systems, the flexibility in cormorant prey choice, and the general lack of suitable baseline data (Wires 2014). While some authors report a negative impact of cormorants on fish populations (Birt et al. 1987; Burnett et al. 2002; Lantry et al. 2002; Rudstam et al. 2004; Winfield et al. 2005; Fielder 2010a; Dorr et al. 2012), others found no impact on fish species of sport or commercial value (Trapp et al. 1999; Wires et al. 2001; Engström 2001; Diana et al. 2006). A major criticism of nearly all studies of cormorant-fish interactions is that the investigators fail to adequately relate cormorant prey consumption to population level impacts on fish, mostly due to a lack of comprehensive fish data. Comprehensive knowledge of prey populations is a critical element to the study of the predator impacts, and attempts to understand complex species interactions are greatly facilitated by long-term trends that integrate short-term fluctuations associated with population stochasticity (Mills and Forney 1988; Brown et al. 2001). A robust analysis of cormorant impacts on fish populations is therefore facilitated by long-term fish population data, as well as a comprehensive record of additional biotic and abiotic factors that also can affect fish population dynamics in the system. One of the few locations in North America with such comprehensive data is Oneida Lake, New York.