Cormorant Predation and the Population Dynamics of Walleye and Yellow Perch in Oneida Lake

Abstract

Double-crested Cormorants (Phalacrocorax auritus) increased dramatically in North America during the 1990s, providing the opportunity to study the effects of an increase of a top predator on an existing predator-prey system. In Oneida Lake, New York, USA, Double-crested Cormorants were first observed nesting in 1984 and had increased to over 360 nesting pairs by 2000. Concomitant with this increase in piscivorous birds was a decrease in the adult walleye (Stizostedion vitreum) and yellow perch (Perca flavescens) populations. Analysis of a 40-yr data series shows higher mortality of subadults (age 1-2 yr perch and age 1-3 yr walleye) for both species in the 1990s compared to the previous three decades. Cormorant diet was investigated from 1995 to 2000 using a combination of cast pellets, regurgitants, and stomach analysis. Walleye and yellow perch were a major portion of the cormorant diet during these years (40-82% by number). The number of subadult walleye and yellow perch consumed by cormorants suggests that the increase in subadult mortality can be explained by predation from cormorants. Mean mortality rates of adult percids attributed to cormorant predation were 1.1% per year for walleye and 7.7% per year for yellow perch. Our analysis suggests that predation by cormorants on subadult percids is a major factor contributing to the decline in both the walleye and the yellow perch populations in Oneida Lake. Other ecosystem changes (zebra mussels, lower nutrient loading, decrease in alternate prey) are not likely explanations because the potential mechanisms involved are not consistent with auxiliary data from the lake and would not affect subadult mortality. The likely impact of bird predation on percid populations in Oneida Lake occurs because cormorants feed on larger fish that are beyond the size range where compensatory mechanisms are important.

Cormorant predation on PIT-tagged lake fish

“…This add to the growing body of evidence that percids (Perca spp.) are particularly vulnerable to cormorant predation (Lantry et al, 2002;Eschbaum et al, 2003;Rudstam et al, 2004;Fielder, 2010;Vetemaa et al, 2010;Bacheler et al, 2011;Emmrich andDuettmann, 2011, Östman et al, 2012, but see Diana et al, 2006). The underlying reason for the apparent preference for perch could be related to the behaviour of the fish in terms of flight response (Cosolo et al, 2010).…”

“…Some studies suggest that the increasing abundance of cormorants has caused long-term declines of local fish populations (Lantry et al, 2002;Rudstam et al, 2004;Koed et al, 2006;Jepsen et al, 2010;Fielder, 2010). Other investigations from both lake and open coastal ecosystems found cormorants to have a low impact on fish communities and fisheries (Linn and Campbell, 1992;Engström, 2001;Barks et al, 2011;Lehikoinen et al, 2011;Östman et al, 2012).…”

Eating the Invaders: The Prevalence of Round Goby (Apollonia melanostomus) in the Diet of Double-Crested Cormorants on the Niagara River

“…Freshwater game fish species of concern include yellow perch, smallmouth bass, stocked salmonids, and occasionally walleye. Studies clearly documenting negative influences of cormorants on freshwater sport fisheries include two investigations conducted on Oneida Lake showing influences on yellow perch and to a lesser extent on walleye populations (VanDeValk et al 2002, Rudstam et al 2004). Published accounts do not clearly document significant mortality and losses due to cormorant predation but provide correlations between cormorant abundance and reduction in game fish stocks (Collis et al 2001;Derby et al 1997;Elrod et al 1997;Ross et al 1995).…”

Double‐Crested Cormorants: Too Much of a Good Thing?

“…The tendency for cormorant predation to mimic recruitment declines (poor reproductive success) is often given as a competing hypothesis to cormorant-caused declines of a fish population. A number of researchers have documented this reduced recruitment effect of cormorant predation on Yellow Perch (O'Gorman and Burnett 2001;Fielder 2008Fielder , 2010, Walleye Sander vitreus (Rudstam et al 2004;Dorr et al 2010;Coleman et al 2016), and Smallmouth Bass Micropterus dolomieu (Lantry et al 2002), with some describing the phenomena as a mortality bottleneck prior to recruitment (Figure 2). This predation effect may reflect foraging cormorants being tied to a breeding colony (central place foraging) for extended periods.…”

“…Schultz et al (2013) hypothesized that this type-III functional re-sponse of cormorants to multiple prey contributed in part to declines of percids in Leech Lake, Minnesota. While such cormorant predation may occur prior to recruitment to a fishery, it likely still comes at life stages beyond where mortality is largely compensatory and is therefore additive, to some degree, on total mortality (Rudstam et al 2004). If this relationship is correct, then cormorant predation mimicking recruitment declines can lead to misinterpretation of predation impacts that will not be revealed until later investigations (Fielder 2008) or will require elaborate modeling exercises (Rudstam et al 2004).…”