Walleye Stocks Research Articles

Mortality of Walleye Eggs and Rainbow Trout Yolk-Sac Larvae in Low-pH Waters of the LaCloche Mountain Area, Ontario

Abstract Freshly fertilized eggs of walleye Stizostedion vitreum were incubated in the outlet waters of George Lake (pH 5.4) and sections of a nearby stream (pH 6.0, 6.6). Ten-day bioassays with yolk-sac larvae of rainbow trout Salmo gairdneri were run concurrently at the walleye sites and at additional sites with low pH (4.6) and with humic water (pH 5.5). Walleye egg mortality was low (25.5–33.5%) at pH 6.0. High mortality (90.5%) occurred between fertilization and the eyed-egg stage at the pH 5.4 site. Mortality of rainbow trout yolk-sac larvae approached 100% within 5 days at both pH 4.6 and 5.4. In contrast, total mortality was less than 3% at pH 6.0 and also in low-pH humic water (pH 5.5). The high mortality of walleye eggs in the acidic outlet waters of George Lake suggests that the acidification of this lake was responsible for the extinction of its walleye stock. The striking differences in mortality of rainbow trout yolk-sac larvae between sites of similar pH (5.4–5.5) indicated that H+-toxicity...

Two Methods for Evaluating Fingerling Walleye Stocking Success and Natural Year-Class Densities in Seven Island Lake, Wisconsin, 1977-1981

The contribution of stocked fingerling walleyes (Stizostedion vitreum vitreum) to the population of 138-acre Seven Island Lake was investigated between 1977 and 1981. Population estimates of fingerling and yearling walleyes were evaluated, using both regression analysis based upon a single sample and catch per effort by electrofishing. Two stocked year classes of walleyes contained 2-3 times as many fish at age 1+ as did three natural year classes. Maximum natural year-class densities did not exceed 1.0 fish/acre at age 0+ or 1+. Population estimates of fingerling and yearling walleyes, using a single sample, were closely correlated with mark-and-recapture estimates. The mean estimated densities of fingerling and yearling walleyes were 0.8 fish/acre and 1.5 fish/acre, respectively, for the mark-and-recapture; 0.9 fish/acre and 1.7 fish/acre, respectively, from a single sample.

Evaluation of Scale Shape for the Identification of Walleye Stocks from Western Lake Erie

Abstract We used the method of Jarvis et al. to characterize scale shapes of five stocks of walleye Stizostedion vitreum vitreum from western Lake Erie, to assess the effects of age, sex, and year of collection on scale shape, and to determine the level of accuracy for assignment of test individuals to their respective stocks based upon their scale shape. Neither sex, age, nor year of collection had significant effects on scale shape of walleyes from the Maumee River, Ohio. Using discriminant analysis we found some differences among scale shape from the five western Lake Erie stocks. The three Ohio stocks (Maumee and Sandusky rivers and Toussaint reef) were more similar in scale shape to each other than to the Lake St. Clair stocks (Clinton and Thames rivers), but classification rates of test individuals to their respective stocks were low. Differences in scale shape were more apparent when we compared an eastern-basin stock (Presque Isle, Pennsylvania) with western-basin groups, yet rates of successful c...

Variation among Stocks of Walleye (Stizostedion vitreum vitreum): Management Implications

Identification of races, strains, or subpopulations of walleye (Stizostedion vitreum vitreum) by examining differences in the morphology or biochemistry has met with relatively limited success. Although there is some genotypic evidence for stock discreteness, most evidence points to differences (age, growth, fecundity, maturity) which are believed to be phenotypic expressions induced by the environment. Thus, in the absence of clear genetic evidence, the biological differences are the reliable means of identifying and managing walleye stocks.Walleye populations are spatially distinct, varying greatly in their rate of growth, rate of maturity, and longevity throughout their distributional range. Any genotypic expression of these population characteristics would probably be masked by environmental influences. There is no concrete evidence that differences in growth, age to maturity, fecundity, and longevity among walleyes are inheritable. The possibility of southern walleye populations being obligative riverine spawners suggests genetic differences, but this needs to be substantiated.Some of the physiological variables used to delineate the responses of stocks to their environment can be useful as management tools to measure their responses to various disturbances, for example, exploitation and habitat modification. Measurement of specific fecundity indicates the relative ability of species to replace themselves. Measurements of mean age of the catch and age of onset of sexual maturity provide information used in protecting the brood stock and rate of maturity indices are more recent examples of these management initiatives.The trend in time responses (mean age, age to maturity, catch per unit effort, etc.) to exploitation of walleye stocks in the Great Lakes and larger inland lakes illustrate the appropriateness of monitoring these variables. Age to maturity, mean age of the catch, and fecundity will also be useful variables in determining the compensatory reserve to population reduction among walleye stocks inhabiting various energy and nutrient regimes. Using examples of heavily exploited walleye populations, we have made an initial attempt to show the degree of compensation in different energy regimes. A crisis curve is given to warn when various walleye stocks are in danger of collapse due to commercial overexploitation.Key words: walleye, phenotypic and genotypic difference, stock, distribution, rate of maturity, fecundity, walleye management

Walleye (Stizostedion vitreum vitreum) Fluctuations in the Great Lakes and Possible Causes, 1800–1975

Changes in walleye (Stizostedion vitreum vitreum) stocks in the Great Lakes from 1800 to 1975 were linked to proliferation of foreign species of fish and culturally induced sources of stress — exploitation, nutrient loading, alteration of spawning habitat, and toxic materials. During the 1800s, three small spawning stocks (and probably many others) were damaged or destroyed because of either overfishing or elimination of spawning habitat through logging, pollution, or damming.During 1900–40, stocks in the Michigan waters of Lake Superior, southern Green Bay, the Thunder Bay River of Lake Huron, the North Channel of Lake Huron, and the New York waters of Lake Ontario declined gradually. Pollution, in general, and degradation of spawning habitat, in particular, probably caused three of the declines and overexploitation was suspected in two instances. In addition, the decline of three of these stocks occurred when rainbow smelt (Osmerus mordax) were increasing.During 1940–75, stocks in seven areas declined abruptly: Saginaw Bay (1944), northern Green Bay (1953), Muskegon River (mid-1950s), western Lake Erie (1955), Nipigon Bay (late 1950s), Bay of Quinte (1960), and Black Bay (mid-1960s). The decline of each stock was associated with a series of weak year-classes. The stocks were exposed to various sources of stress, including overexploitation, pollution, and interaction with foreign species, which, if not important in the decline, may be suppressing recovery. Only the western Lake Erie stock recovered, in part due to a reduction in exploitation and, possibly, because of the relatively low density of smelt and alewives (Alosa pseudoharengus) in the nursery areas.Relatively stable stocks persisted in five areas: Wisconsin waters of Lake Superior, Lake St. Clair — southern Lake Huron, eastern Lake Erie, northern Lake Huron, and parts of Georgian Bay. Pollution problems were relatively minor in these areas and exploitation was light during recent decades. Apparently these stocks were more capable of withstanding the additional stresses exerted by alien species. Key words: population fluctuations, Percidae, Stizostedion, Great Lakes walleye, history of fisheries, summary of stresses, harvests, management implications

Percids in the Canadian Waters of Lake Huron

Percids have never dominated the commercial catch from Canadian waters of Lake Huron but coincident with declining salmonid production, they contributed about 17% of the commercial landings from 1940 to 1975. Walleye (Stizostedion vitreum vitreum) production declined gradually over the past century whereas yellow perch (Perca flavescens) production increased irregularly since 1910.Walleye occur in relatively discrete stocks associated with rivers, inlets, and estuaries in the North Channel and Georgian Bay whereas southern Lake Huron stocks are seasonal residents of the southeastern rim of the main basin. Yellow perch are ubiquitous throughout the littoral waters of the lake. Growth rates of walleye are similar to those for more southerly populations in the Great Lakes and year-class strength is highly variable. Angling and commercial fishing contribute significantly to mortality rates in exploited stocks but deteriorating environmental conditions are probably more important to the persistence of walleye stocks in Lake Huron. At least one stock is presently threatened by industrial acidification of the watershed. Key words: Percidae, Lake Huron, production, population biology, Stizostedion, Perca

Lake Superior: Effects of Exploitation and Introductions on the Salmonid Community

Lake Superior is highly oligotrophic and not very productive. It has not, however, been much affected by man's activities. Substantial quantities of woody allochthonous materials entered the lower reaches of tributaries and their estuaries from the pioneer lumbering industry. These undoubtedly depreciated the shallow-water benthic environment and may have adversely affected fish stocks in the immediate areas concerned, especially those of lake sturgeon (Acipenser fulvescens) and lake whitefish (Coregonus clupeaformis). At present, local areas of urban or industrial pollution can be identified but, in general, appear to have had little adverse effect on fish stocks, although the collapse of one walleye stock has been attributed to pollution from a paper mill. Every commercial species has, however, been severely depleted. Recent declines can be correlated with predation by sea lamprey (Petromyzon marinus) but, without exception, all species give evidence of extensive overfishing long before sea lamprey entered the lake. That this has not been more obvious is due to the stratification of catch statistics by arbitrary geographic areas (statistical districts) which are too large to relate meaningfully to either fish distributions or patterns of fishery operations. Because fish are generally distributed as local, often small, quasi-discrete stocks, they were exploited sequentially by the young, developing fishery. In this way stock after stock was depleted while conventional yield statistics gave an impression of relative stability. The lag before these statistics indicated the decline appears to be related to the degree of dispersal characteristic of each species. Thus the decline of the sturgeon was first evident, that of the lake trout (Salvelinus namaycush) last. Recovery has been slight but modern hatchery technology clearly provides a prospect for rejuvenating existing stocks or developing new ones. In either case, such synthetic populations will offer favorable opportunities for detailed investigation of the nature of fish distribution and its bearing on the interpretation of catch statistics.

Dynamics and Exploitation of Mature Walleyes, Stizostedion vitreum vitreum, in the Nipigon Bay Region of Lake Superior

Walleye stocks in Nipigon Bay of Lake Superior were homogeneous with those in tributary inland waters but were discrete from Black Bay stocks. Returns from 2200 tagged walleyes in Lake Superior and tributary inland waters between 1955 and 1958 varied from 7.8 to 31.0% for 2 years after release. The commercial fishery in Lake Superior recovered 64.9% of the tags, the sports fishery in inland waters captured 27.6%. Fish tagged in the Nipigon River travelled a mean distance of 11.8 miles from the point of release and were recovered in 191 days (average). Total mortality rates for Nipigon Bay walleyes were 55.0% (1955–57). Mature walleyes on the spawning grounds in the Nipigon River in 1957 were estimated at 22,000, and fish in Nipigon Bay over 14 inches (total length) the same year at 41,000. All male walleyes were mature at 15 inches and females at 18 inches. Walleyes exploitation rates increased with the decline of the lake trout fishery. Wounding and scarring rates by sea lampreys increased during 1955–57 but never exceeded 1.0% on adult walleyes. Severe pollution on the west side of Nipigon Bay originated from a kraft mill. High concentrations of total solids and dense sedimentation of wood fibres created an environment unfavourable to Hexagenia limbata and Pontoporeia affinis. The recent elimination of the walleye fishery in Nipigon Bay is most likely attributable to industrial pollution rather than to overexploitation or sea lamprey predation.