Geology topics

David R. Wolfert

Publications and source records attributed to David R. Wolfert.

10 recordsLinked to original sources

USGS1992

Selection of prey by walleyes in the Ohio waters of the central basin of Lake Erie, 1985-1987

Walleyes (Stizostedion vitreum vitreum) were collected at five locations in the central basin of Lake Erie in 1985-87. The contents of the fishes' stomachs were examined to identify the species of prey. The seasonal availability of potential prey was determined from sampling with trawl tows. Food electivity indexes for young-of-the-year (YOY) and older walleyes were calculated. Electivity indexes changed monthly in YOY walleyes that consumed mostly YOY gizzard shads (Dorosoma cepedianum) in July and fed moderately on gizzard shads, but more on smelts (Osmerus mordax), in August. In September and October YOY walleyes did not consume YOY white perch (Morone americana). During October, they continued to eat YOY gizzard shads moderately but consumed mostly emerald shiners (Notropis atherinoides). Older walleys were highly partial to YOY gizzard shads, emerald shiners, and smelts and consumed no YOY white perch. The numbers of YOY yellow perch (Perca flavescens) in stomachs were limited. Prey selection by walleyes in the central basin was species-specific irrespective of abundance of prey.

Resource Publication↗

USGS1986

Changes in growth and maturity of walleyes associated with stock rehabilitation in western Lake Erie, 1964-1983

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 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.

North American Journal of Fisheries Management↗

USGS1978

Age, growth, and food of northern pike in eastern Lake Ontario

Northern pike ( Esox lucius ) from eastern Lake Ontario were sampled with gill nets and trap nets in 1972-1973. Fish of age-groups IV, V, and VI were predominant in the catch. Although males were slightly longer after the 1st yr of life, females gained a 25-mm advantage in the 2nd yr and a 30-mm advantage in the 3rd yr. In later years, the increments of growth of males and females were similar. All males were mature after 2 yr and females after 3 yr. The stomachs of northern pike contained only fish; the alewife ( Alosa pseudoharengus ) was the principal forage species consumed. Electivity indexes for alewives, white perch ( Morone americana ), and yellow perch ( Perca flavescens ), the three most common species in the diet, indicated a positive selection for alewives that increased from June to October during a period when the relative abundance of alewives steadily decreased.

Transactions of the American Fisheries Society↗

USGS1978

Movements of walleyes tagged in eastern Lake Erie

In May, October and November of 1968, 2,456 walleyes of various ages were captured, tagged and released in eastern Lake Erie to determine seasonal movement of walleyes in that basin and the degree to which they intermingled with fish of the central and western basins. From 1968 to 1971, 275 of the tagged fish were recovered. Walleyes tagged in the spring on spawning grounds near Barcelona (N.Y.) moved northeasterly along the shore soon after spawning and spent the summer near the Buffalo-Niagara River Inlet area. Later returns indicated that they then reversed their direction of travel in late summer and fall and followed the shoreline back toward the spawning grounds off Barcelona. Young fish, tagged in the fall, also showed this pattern the following year. Westward movement into the central basin was insignificant, and no recoveries were reported from Canadian waters. Therefore, it is concluded that walleye populations in the United States waters of eastern Lake Erie are geographically separate from those in the western basin and that their management should be based on this inference.

New York Fish and Game Journal↗

USGS1977

Age and growth of the walleye in Lake Erie, 1963-1968

Age and length distributions are given for 6,764 walleyes, Stizostedion v. vitreum (Mitchill), sampled during 1963-1968 from commercial landings of walleyes representing discrete populations in the eastern and western basins of Lake Erie. In the eastern basin, where all catches were made with gill nets, age-groups III and IV predominated in samples from large-mesh nets and age-group I in samples from small-mesh nets. In the western basin, where nearly all walleyes were taken in trap nets, age-groups I and II predominated in 1963-1965, and II and III in 1966-1968 (after the legal commercial size limit was raised from 330 to 394 mm). Study of 5,082 walleyes from the two basins showed that at any given age during the first 3 years of life, females were longer than males and, on the average, fish from the western basin were longer than those from the eastern basin. The greatest difference in growth of fish of the same sex for the two basins was apparent at the end of the first year of life, when fish from the eastern basin were only about half as heavy as those from the western basin. After the second year, relative growth in weight of fish in the eastern basin improved: the weight of females exceeded that of females in the western basin by the end of the fourth growing season and the weights of males in the two basins were about equal by the end of the sixth growing season.

Transactions of the American Fisheries Society↗

USGS1968

An improved girthometer for studies of gill net selectivity

Gill nets are effective for collecting samples of many fish species. These nets may be highly selective in their catch, depending on the mesh size or sizes used and on the size distribution and body shape of the fish in the population. Early studies related mesh selectivity to length or, in a few instances, to length and weight. Later studies showed that the selectivity of gill nets was related more closely to the girth of the fish than to the length, weight, or a combination of these. The girthometer presented here was designed for rapid and accurate measurement of the fish girth. Both speed and accuracy are important when very large numbers of fish are sampled for mesh-selectivity studies. It is also important that a girthometer be sturdy and rigid enough to provide accurate measurements in spite of rough handling and difficult working conditions.

Progressive Fish-Culturist↗

USGS1968

Distribution and abundance of the Japanese snail, Viviparus japonicus, and associated macrobenthos in Sandusky Bay, Ohio

A survey of the macrobenthos of Sandusky Bay, Lake Erie, in June, 1963, provided information on the abundance and distribution of the introduced Japanese snail, Viviparus japonicus, which has become a nuisance to commercial seine fishermen. The abundance and distribution varied considerably within the bay; at the time of the survey, most snails were found near the north-central shore. Environmental characteristics were nearly uniform and had no apparent effect on the distribution; concentrations in different areas at different times appeared to result from water movements induced by winds. The time of the study coincided with a period of reproduction; young-of-the-year snails were most abundant in areas where adults were most common. The frequency distributions of shell height and diameter suggested the presence of two age groups of adults in the population. Considerable natural mortality was seen, both at the time of the study and in other seasons. Only three other gastropods were observed in the bay; the most abundant was another viviparid, Campeloma decisum. Other mollusks present were four species of Sphaeriidae and 18 species of Unionidae. A summary of invertebrates found, other than the mollusks, is also presented.

Ohio Journal of Science↗

USGS1967

Infection of the walleye, Stizostedion v. vitreum, of western Lake Erie with Bothriocephalus cuspidatus (Cooper)

In recent years appreciable changes have taken place in the biota and physiochemical conditions in Lake Erie. The accelerated eutrophication of the lake has been accompanied by the near disappearance of several fish species, e.g., blue pike (Stizostedion vitreum glaucum), lake herring (Coregonus artedi), lake trout (Salvelinus namaycush), sauger (Stizostedion canadense), and whitefish (Coregonus clupeaformis). Interest in the biology of the remaining species has increased as means have been sought to preserve their numbers in the lake. This report, which describes the caecal and intestinal parasites of the walleye, Stizostedion vitreum vitreum, is a contribution to the natural history of this fish in western Lake Erie. This study concerns: the type and degree of intestinal parasitic infestations in a single year class of walleyes during their first 3 years of life; seasonal changes in the incidence and maturity of the dominant parasite Bothriocephalus cuspidatus; and the effects of the infestations on the physical condition of the host.

Papers of the Michigan Academy of Science, Arts, a↗

USGS1966

Food of young-of-the-year walleyes in Lake Erie

Stomach contents were examined for 794 young-of-the-year (0-group) walleyes (Stizostedion vitreum vitreum) captured by trawls at 17 locations in western Lake Erie in June-November 1962. Food organisms were found in 92.5 percent of the stomachs. Food varied with geographic location and season of capture, but within areas and seasons, selection for certain species and sizes of prey was strong. Walleyes from the extreme western end of Lake Erie fed primarily on gizzard shad and alewives during the summer and shifted to emerald shiners during the fall. The stomach contents of walleyes from the Island region changed from mainly yellow perch during the summer to emerald shiners by the end of the year. Walleyes collected east of the Islands had consumed only smelt and yellow perch. The numbers of forage species caught with walleyes in trawls showed little correlation with the representation of these species in walleye stomachs. Walleyes fed on the smallest individuals of each species regardless of species preferences.

Fishery Bulletin↗

USGS1963

The movements of walleyes tagged as yearlings in Lake Erie

A total of 3,998 yearling walleyes, Stizostedion vitreum vitreum (Mitchill), were captured, tagged, and released along the south shore of western Lake Erie to determine their movements and their dispersal from a known nursery area. Four hundred ninety-nine recoveries were made over a period of 3 years. Tagged walleyes traveled primarily north toward the islands in the Western Basin during their first year of liberation, and in succeeding years moved progressively toward the extreme western end of the lake. Some walleyes were recaptured within 6 months in the Detroit River, Lake St. Clair, the St. Clair River, and southern Lake Huron, and the percentage of fish recaptured in these waters north of Lake Erie increased annually. Movement eastward into the Central and Eastern Basins of the lake appeared negligible. The greatest distance traveled by a marked walleye was 236 miles. The average distance traveled by all tagged fish was 25 miles.

Transactions of the American Fisheries Society↗