Anthony J. VanDeValk

CORMORANT PREDATION AND THE POPULATION DYNAMICS OF WALLEYE AND YELLOW PERCH IN ONEIDA LAKE

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...

Comparison of Angler and Cormorant Harvest of Walleye and Yellow Perch in Oneida Lake, New York

Abstract Since at least the beginning of the last century, sport anglers and commercial fishers have often held cormorants responsible for declining catches. The recovery of double-crested cormorant Phalacrocorax auritus populations throughout the Great Lakes region since the late 1970s has rekindled efforts to assess their impact on sport fish populations. In this paper we compare the species and age composition of fish consumed by double-crested cormorants (diet study) and harvested by anglers (creel survey) with abundance estimates of walleyes Stizostedion vitreum and yellow perch Perca flavescens (mark-recapture and catch per unit effort). The numbers of walleyes consumed by cormorants were similar to those harvested by anglers; however, cormorants consumed only subadults, whereas anglers harvested only age-4 and older adults. Cormorants and anglers combined harvested 7% of age 1-3 walleyes and 14% of the adult walleye population. Cormorant consumption of adult yellow perch was similar to angler harve...

Size-Dependent Alewife Predation on Larval Walleyes in Laboratory Experiments

Abstract Alewives Alosa pseudoharengus can be significant predators on larval fish, and fishery managers must consider potential predation when developing stocking strategies. We conducted laboratory experiments to determine sizes of larval walleyes Stizostedion vitreum that alewives can capture. Adult alewives (122 ± 1.52 mm total length, TL) preyed intensely on larval walleyes from the time the larvae hatched until they reached about 16 mm TL. All larval walleyes smaller than this size were captured on the first strike by an alewife. Avoidance behavior by larval walleyes was first observed when they reached 16–19 mm TL, and although some survived the first strike, all were consumed by the end of 1 h. When larvae averaged about 25 and 30 mm TL, few were captured on the first strike, and 75% and 33%, respectively, were consumed within 1 h. When larvae were about 34 mm TL, only 5% were eaten by the end of 1 h. Alewife gape height and width were both about twice as large as the largest larval walleye body h...

Depensatory Mortality, Density-Dependent Growth, and Delayed Compensation: Disentangling the Interplay of Mortality, Growth, and Density during Early Life Stages of Yellow Perch

Abstract We present long-term (>40-year) patterns in the density of age-0 yellow perch Perca flavescens in Oneida Lake at four early life stages (at egg deposition, at the attainment of a total length of 18 mm, on 1 August, and on 15 October), from which we calculated mortality and growth rates during the three intervals between these early life stages. At each of these stages, age-0 yellow perch densities have been lower in recent years than in the 1960s and 1970s. Mortality rates showed no time trend from egg to 18 mm (interval 1 [the larval stage]), increased from 18 mm to 1 August (interval 2 [the limnetic stage]), and decreased from 1 August to 15 October (interval 3 [the demersal stage]). We also tested previous hypotheses for density-dependent effects on mortality and growth using the entire long-term data set. Contrary to expectations from the 1960s, the mortality rates of age-0 yellow perch in Oneida Lake are no longer depensatory. Overall, the growth rate of age-0 yellow perch has increased over...

GIZZARD SHAD PUT A FREEZE ON WINTER MORTALITY OF AGE-0 YELLOW PERCH BUT NOT WHITE PERCH

Four decades of observations on the limnology and fishes of Oneida Lake, New York, USA, provided an opportunity to investigate causes of mortality during winter, a period of resource scarcity for most juvenile fishes, in age-0 yellow perch (Perca flavescens) and age-0 white perch (Morone americana). This time series contains several environmental (e.g., winter severity) and biological (e.g., predator abundance) signals that can be used to disentangle multiple effects on overwinter mortality of these fishes. A multiple regression analysis indicated that age-0 yellow perch winter mortality was inversely related to fish length in autumn and to the abundance of alternative prey (gizzard shad [Dorosoma cepedianum] and white perch). However, no length-selective predation of yellow perch by one of the main predators, adult walleye (Sander vitreus), was detected. In contrast, white perch mortality was directly associated with total predator biomass and abundance of white perch in autumn, and inversely related to yellow perch abundance as a potential buffer species, but not to the abundance of gizzard shad. Winter severity was not a significant predictor of mortality for either perch species. Predicted winter starvation mortality, from a model described in the literature, was much lower than observed mortality for yellow perch. Similar models for white perch were correlated with observed mortality. These results collectively suggest that predation is the main mechanism shaping winter mortality of yellow perch, while both predation and starvation may be important for white perch. This analysis also revealed that gizzard shad buffer winter mortality of yellow perch. Although winter duration determines the northern limit of fish distributions, in mid-latitude Oneida Lake and for these species, predator-prey interactions seem to exert a greater influence on winter mortality than starvation.

Survival and Growth of Intensively Reared Large Walleye Fingerlings and Extensively Reared Small Fingerlings Stocked Concurrently in Small Lakes

Abstract Size of walleyes Stizostedion vitreum at the time of stocking is thought to play a key role in determining the success of stocking programs. Because starvation and predation risk are size-dependent processes, fingerlings stocked at larger sizes are expected to survive better than fingerlings stocked at smaller sizes. However, large fingerlings often require different culture techniques that make them more expensive to produce. Therefore, large fingerlings should only be used if returns are high enough to offset costs. We evaluated the relative success of two sizes of stocked walleye fingerlings in four lakes in New York State. For four consecutive years (1993–1996), each lake was stocked with equal densities (50 fish/ha) of small (30–50-mm), extensively reared pond fingerlings in June and large (120–140-mm), intensively reared fall fingerlings in September. In October, we electrofished each lake to determine growth and survival of stocked fingerlings. Despite being stocked at a much later date, a...

Angler Catch Rates and Catchability of Walleyes in Oneida Lake, New York

Abstract Understanding the relationship between anglers and fish is important to the management of angling fisheries. We compared angler catch rates estimated from creel surveys with (1) population density estimates of age-3 and older walleyes Sander vitreus based on mark–recapture and (2) mean growth of walleyes aged 4–6 in Oneida Lake during 1957–1959, 1997, and 2002– 2003. We also compared walleye catchability to walleye population density. Angler catch rates were not related to walleye population density; however, by combining population density and walleye growth, we were able to explain 97% of the variability in angler catch rates, perhaps because growth rates were related to prey abundance. Catchability of walleyes decreased as population density increased. Consideration of these effects should improve our understanding of angler–fish dynamics and allow fishery managers to better predict the effects of management actions.

Comparisons between consumption estimates from bioenergetics simulations and field measurements for walleyes from Oneida Lake, New York

Abstract Daily consumption was estimated from the stomach contents of walleyes Sander vitreus collected weekly from Oneida Lake, New York, during June-October 1975, 1992, 1993, and 1994 for one to four age-groups per year. Field rations were highly variable between weeks, and trends in ration size varied both seasonally and annually. The coefficient of variation for weekly field rations within years and ages ranged from 45% to 97%. Field estimates were compared with simulated consumption from a bioenergetics model. The simulation averages of daily ration deviated from those of the field estimates by −20.1% to +70.3%, with a mean across all simulations of +14.3%. The deviations for each time step were much greater than those for the simulation averages, ranging from −92.8% to +363.6%. A systematic trend in the deviations was observed, the model producing overpredictions at rations less than 3.7% of body weight. Analysis of variance indicated that the deviations were affected by sample year and week but not...

Relationships between Relative Weight, Prey Availability, and Growth of Walleyes in Oneida Lake, New York

Abstract Assessment of predator–prey dynamics is a central feature of community-based fisheries management, and a variety of fish condition indices have been developed from length–weight data to make inferences about feeding conditions. Relative weight (Wr ) is useful for measuring fish condition, is easily calculated, and has simple data requirements; however, few studies have empirically validated Wr indices. We compared the Wr of walleyes Sander vitreus in Oneida Lake, New York, with prey fish availability and walleye growth observed over 23 years (1961–1983). For each year, we calculated the Wr for three length-classes (350, 400, and 450 mm total length) of walleyes caught in October. Prey fish availability was calculated from annual estimates of (1) prey biomass in bottom trawl catch and (2) biomass of age-3 and older walleyes estimated from mark–recapture studies. Growth of walleyes (ages 4–6) was determined using lengths at age that were back-calculated from scale annuli. The Wr declined as walleye...

Influence of Party Size and Trip Length on Angler Catch Rates on Oneida Lake, New York

Abstract Angler catch rates have been used to compare angler success in sport fisheries among years or systems, to assess relative fish abundance, and to evaluate management efforts. Understanding the factors that influence angler catch rates is critical for the proper interpretation and application of these data. Information for 10,998 angler trips was collected through an angler diary program conducted during 1994–1998 and direct-contact roving creel surveys conducted during 1997 and 2002–2004 to examine the influences of angler party size and trip length on the catch rates for walleye Sander vitreus, smallmouth bass Micropterus dolomieu, and yellow perch Perca flavescens at Oneida Lake, New York. Party size and trip length were correlated; therefore, we constructed separate models combining data for year, party size, and trip length to examine the relationship between these factors and the angler catch rate. In both the diary program and the creel survey, the angler catch rates for all species decrease...