Analysis of Compensatory Responses in Land-Locked Alewives to Walleye Predation: A Tale of Two Lakes

Abstract

We compared one established population (Cayuta Lake) and one expanding population (Canadarago Lake) of landlocked alewives Alosa pseudoharengus to evaluate compensatory responses of alewives to predation by walleyes Sander vitreus. Alewives have been present in Cayuta Lake since at least 1977, and during the years 1995 to 2009 the population ranged from 24,470 fish/ha in 2000 to 3,800 fish/ha in 2007. Alewives were first observed in Canadarago Lake during 1999, and the population remained at low densities (<26 fish/ha) until reaching 370 fish/ha in 2006 and 1,050 fish/ha in 2009. Differences in zooplankton reflected higher planktivory rates in Cayuta Lake than in Canadarago Lake. Density of age-3 and older walleyes was higher in Canadarago Lake (21–24 fish/ha) than in Cayuta Lake (12–14 fish/ha), despite elevated stocking rates of fingerling walleyes in Cayuta Lake during 2002–2006. Alewife density explained 77–84% of the variation in alewife length at age and 48–84% of the variation in condition (ages 0, 1, and 2) among years and lakes. Alewife length at age under low densities in Canadarago Lake was similar to observations in anadromous populations. Alewife recruitment (number of fall age-0 recruits/spawner) was higher in Canadarago Lake than in Cayuta Lake. The combined data yielded a Beverton–Holt stock–recruitment curve that rose rapidly at low alewife densities, and 50% of the maximum recruitment was predicted to occur at 400 spawners/ha. Compensatory responses of alewives at low densities include decreased cannibalism and increased growth rates of both adults and age-0 fish. Compensatory responses should be considered when evaluating the piscivore levels needed to control alewife populations or, conversely, when evaluating the risk of alewife population collapse in response to increased predation rates. Although alewife abundance declined in response to the experimental walleye stocking in Cayuta Lake, we were unable to increase the walleye population sufficiently to decrease alewife recruitment.

Received November 27, 2010; accepted May 10, 2011

ACKNOWLEDGMENTS

We thank Norm McBride at the Department of Environmental Conservation (DEC) Region 4 and David Green for help with sampling Canadarago Lake; the staff at DEC Regions 4 and 8, Oneida Fish Cultural Station, and Bath Fish Hatchery for stocking walleyes in Cayuta Lake; Roland Wang, Kathleen Marean, Rahmat Naddafi, Jonathan Swan, Chris Hotaling, Tony VanDeValk, William Fetzer, and Victoria Whitenour for help with sampling and laboratory processing; and Jeff Loukmas, Jeff Schaeffer, Patrick Kocovsky, and an anonymous reviewer for helpful comments on the manuscript. Maureen Walsh and Robert O’Gorman provided advice on alewife aging. We are also grateful to John Seeley for the gracious use of his dock and help in the field and to the angler cooperators for help with understanding catch rates. Funding for this project was provided by the New York Federal Aid in Sport Fish Restoration Program (Grant F-56-R to Cornell University). Funding for the Schuyler County Soil and Water Conservation District was provided in part by the Finger Lakes/Lake Ontario Watershed Protection Alliance. This is Contribution Number 283 from the Cornell Biological Field Station.