Changes in Growth and Maturity of Walleyes Associated with Stock Rehabilitation in Western Lake Erie, 1964-1983

Abstract

The precipitous decline in abundance of walleyes (Stizostedion vitreum vitreum) in western Lake Erie during the 1960s caused major concerns for the future of this resource. Mercury contamination in walleyes in 1970 resulted in a moratorium on commercial fishing in United States and Canadian waters. The opportunity arose for resource agencies to develop a plan for rehabilitation of the walleye stocks, and quota management for walleyes was begun in 1976. After 8 years, the resource had recovered dramatically and the estimated standing stock in 1983 was more than three times that in 1976. In the mid‐1970s, however, certain detrimental changes suggested that self‐regulatory mechanisms were occurring. The growth rate declined gradually but rather consistently. Growth changes were most evident for young‐of‐the‐year (YOY), yearlings, and 2‐year‐old fish, which usually constituted more than 80% of the standing stock in 1976‐1983. Average lengths of YOY fish in the fall decreased by nearly 50 mm (from about 240 mm in 1961 to 190 mm in 1983). Average lengths and weights of yearling and older fish began to decline after 1975 and decreased markedly after 1980. Historically, growth of walleyes in western Lake Erie exceeded that reported for many walleye populations in other waters. Another sign of self‐regulation was an increasing delay in the onset of maturity. Most (usually more than 90%) of the yearling males were sexually mature each fall before 1979, but this percentage decreased to only 32 by fall 1983. Usually 80% or more of the age‐II females were mature each fall during the 1960s and early 1970s, but this percentage decreased rapidly to only 7 by fall 1983. Prey fish populations declined somewhat in the early 1980s, and their ability to sustain the high abundance of walleyes is a great concern to resource managers.

Individual-Based Model of Yellow Perch and Walleye Populations in Oneida Lake

“…Yellow perch and walleye also provide an excellent case study of density dependence. Studies by Forney (1965Forney ( , 1971Forney ( , 1974Forney ( , 1976Forney ( , 1977a, and others (Tarby 1974, Neilson 1980, Serns 1982, Muth and Wolfert 1986, Buijse and Houthuijzen 1992 indicate these species (and congeneric pikeperch Stizostedion lucioperca and European perch Perca fluviatilis) show strong compensatory responses in growth and age at maturity to changes in mortality.…”

“…3 is based on fitting a function to values of the fraction of females mature (as determined by length), intermediate to those observed for fast and slow walleye growth periods in Lake Erie (Muth and Wolfert 1986). For typical lengths at age, 57% of age-3 yellow perch and 35% of age-5 walleye are mature.…”

“…Similar density-dependent changes in survival, growth, and maturation have been reported for yellow perch and walleye in other systems (see Saila et al 1987). For example, Muth and Wolfert (1986) reported that a 3-fold increase in the walleye stock in western Lake Erie during the years 1976-1983 resulted in shorter mean lengths of age-2 females and a drop from 90% to 7% in the percent mature of age-2 females. In other studies, European perch in Windermere exhibited density-dependent growth (Le Cren et al 1972).…”

Indication of Density‐Dependent Changes in Growth and Maturity of the Barndoor Skate on Georges Bank

“…Although previous elasmobranch studies have not addressed changes in maturity as a result of a biomass increase, several studies in teleosts have suggested that increased competition for fewer available resources can result in delayed maturation and lower reproductive potential, creating an overall compensatory shift in the population (Rose et al 2001). For example, the percentage of mature age-1 male Walleyes Sander vitreus in Lake Erie declined from 99% after drastic population depletion to 32% after the population had recovered in Lake Erie (Muth and Wolfert 1986). In addition, studies on Silver Hake Merluccius bilinearis in the northwest Atlantic Ocean suggest that sexual maturity can be delayed when stock abundance is increased due to added competition (Helser and Almeida 1997).…”

Diet overlap and consumption patterns suggest seasonal flux in the likelihood for exploitative competition among piscivorous fishes

“…Most evidence for competition among piscivorous fishes has been indirect, such as correlations between prey density and predator growth, condition and biomass (Ploskey & Jenkins 1982;Muth & Wolfert Abstract -Competition, both intraspecific and interspecific, among piscivorous fishes (predators) may be more pronounced in reservoirs because of the artificial nature of these systems and the continuous anthropogenic influences that may not allow natural processes to regulate their densities. Most evidence for competition among piscivorous fishes has been indirect, such as correlations between prey density and predator growth, condition and biomass (Ploskey & Jenkins 1982;Muth & Wolfert Abstract -Competition, both intraspecific and interspecific, among piscivorous fishes (predators) may be more pronounced in reservoirs because of the artificial nature of these systems and the continuous anthropogenic influences that may not allow natural processes to regulate their densities.…”