John L. Forney

Impact on Daphnia pulex of Predation by Young Yellow Perch in Oneida Lake, New York

Abstract The response of a Daphnia pulex population to fluctuations in abundance of young (age-0) yellow perch Perca flavescens was examined in Oneida Lake, New York, 1975–1979. Comparison of yellow perch biomass and Daphnia pulex abundance suggested daphnid populations could tolerate predation by 10 kg of young fish˙hectare-1 but reproduction could not compensate for predation when biomass of young exceeded 20–40 kg˙hectare-1. Consumption by young yellow perch exceeded Daphnia pulex production in 1975 and 1977, when daphnids disappeared, but maximum daily consumption was less than 27% of production in 1976 when daphnids were abundant through late summer. Since 1968, D. pulex populations have persisted through late summer in years when young yellow perch were scarce and disappeared when young were abundant. The decisive role of young yellow perch in the regulation of Daphnia pulex abundance is of importance to the broader fish community in Oneida Lake.

Interactions Between Yellow Perch Abundance, Walleye Predation, and Survival of Alternate Prey in Oneida Lake, New York

Abstract Species of forage fish in stomachs of walleye and their abundance in trawl catches were compared in 1968–71. Young yellow perch were the predominant species in trawls and were consistently selected by walleyes. Consumption of young white perch and walleyes by older walleyes increased during periods of low yellow perch abundance which suggested that young yellow perch might act as a buffer controlling intensity of predation. This possibility was assessed by comparison of relative survival of white perch and walleye cohorts between the first and second year of life with indices of yellow perch density between 1959 and 1970. Close correlations between these variables support the conclusion that abundance of young perch governs intensity of predation on other forage size fish and indirectly controls the size of the walleye population by regulating cannibalism.

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...

INDIVIDUAL‐BASED MODEL OF YELLOW PERCH AND WALLEYE POPULATIONS IN ONEIDA LAKE

Predator–prey dynamics and density dependence are fundamental issues in ecology. We use a detailed, individual-based model of walleye and yellow perch to investigate the effects of alternative prey and compensatory responses on predator and prey population dynamics. Our analyses focus on the numerical and developmental responses of the predator, rather than the traditional emphasis on functional responses. The extensive database for Oneida Lake, New York, USA was used to configure the model and ensure its realism. The model follows the daily growth, mortality, and spawning of individuals of each species through their lifetime. Three ecologically distinct periods in the history of Oneida Lake were simulated: baseline, high mayfly densities, and high forage fish densities. Mayflies and forage fish act as alternative prey for walleye. For model corroboration, the three periods were simulated sequentially as they occurred in Oneida Lake. Model predictions of abundances, size at age, and growth and survival ra...

Trophic Dynamics and Development of Freshwater Pelagic Food Webs

The open water or pelagic zones of lakes are characterized by complex interactions that sometimes include edge effects from nearshore and near-bottom areas (Hutchinson 1957). The freshwater pelagia occur in water bodies ranging from small lakes to the world’s great lakes and communities inhabiting this zone are affected by small- to large-scale physical, chemical, and biological processes. Community interactions in pelagic food webs are trophically dynamic and are governed by nutrient limitation, competition, predation, and other ecological forces. Rate processes in pelagic food webs are generally faster than those in terrestrial systems (Paine 1980) and consequently producer controlled and consumer controlled trophic level interactions are more readily observed. Freshwater pelagic food webs have been studied intensively in this century and there is growing awareness of their complexity and uniqueness in aquatic ecology (Persson et al. this volume).

Energetics, Food Consumption, and Growth of Young Yellow Perch in Oneida Lake, New York

Abstract A study to determine the energy content of young (age-0) yellow perch Perca flavescens and their prey, measure metabolism, and relate energy supply and intake to fish growth was conducted in Oneida Lake, New York during the summers of 1975–1977. Growth rates in these years were similar in early summer when young yellow perch were 20 to 50 mm total length and fed almost exclusively on Daphnia pulex but varied widely in late summer when the diet was more diverse. In early summer, food intake averaged 23% of body energy content, young yellow perch assimilated about 68% of the daily ration, and gross efficiency averaged 27%. Comparison of observed growth and energy available for growth calculated from an energy budget indicated estimates of food intake and respiration were reasonable. In years when the D. pulex population collapsed in late summer, young yellow perch shifted to alternate prey and growth declined. Variation in first-year growth, mediated by D. pulex abundance, may determine the contrib...

Development of Dominant Year Classes in a Yellow Perch Population

Abstract Abundance of young-of-the-year yellow perch in Oneida Lake, New York was estimated in 1959 through 1968 by shore seining in July and trawling in late summer. Seine and trawl catches were high in 1960, 1962, 1964, and 1968 and catches of age I+ perch in subsequent years confirmed that these were dominant year classes. Variation in numerical size of year classes was less in the first year than in the second which indicated a divergence in year class abundance. Estimates of mortality based on the catch in trawls from August to October confirmed that weak year classes generally experienced higher mortality than strong year classes, thus mortality was depensatory. Changes in year class bio-mass and estimates of perch consumed by the walleye population were consistent with the assumption that depensatory mortality was caused by predation.

Diet, Growth, and Potential Competitive Interactions between Age-0 White Perch and Yellow Perch in Oneida Lake, New York

Abstract Diet and growth of age-0 white perch Morone americana and age-0 yellow perch Perca flavescens were compared during July–October 1980 and 1987. Both fish species fed on Daphnia pulex in 1980 and growth was rapid; prey biomass per gram of fish was 2–12 times higher for white perch than for yellow perch. In 1987, white perch consumed up to three times more prey biomass than yellow perch, but the subsequent disappearance of D. pulex caused both fish species to switch to macroinvertebrates and growth of both species declined. Between 1977 and 1987, mean weights and specific growth rates of white perch exceeded yellow perch by October in all years, and weights of white perch were closely tied to the density of D. pulex in late summer–early fall (Spearmans rank correlation = 0.58, P = 0.07). Diet overlap for age-0 white and yellow perch was high when D. pulex was present, and the potential for interspecific competition was greatest when these fish were similar in length. Because of a prolonged spawning...

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...

Reduction in recruitment of white bass in Lake Erie after invasion of white perch

Abstract Recruitment to the adult population of white bass Morone chrysops in Lake Erie sharply declined during the early 1980s. To explain this phenomenon, we formulated the following four hypotheses: (1) the biological characteristics of adult spawners changed during the early 1980s, so that the ability to produce eggs decreased; (2) the decrease in phosphorus loadings to Lake Erie during the 1970s resulted in a lower abundance of crustacean zooplankton and thus in reduced survival of age-0 white bass; (3) the increase in the population of adult walleyes Stizostedion vitreum in Lake Erie during the 1970s and 1980s led to reduced survival of age-0 white bass; and (4) establishment of the white perch Morone americana population in Lake Erie during the early 1980s led to reduced survival of the early life stages of white bass. The growth, maturity, and fecundity of adults during the period 1981–1997 were compared with the same characteristics found by earlier studies. The mean length, weight, and condition...