Geology topics

Stephen J. Nepszy

Publications and source records attributed to Stephen J. Nepszy.

6 recordsLinked to original sources

USGS1990

Management of percids in Lake Erie, North America

Lake Erie's fish populations and their habitats have undergone very substantial changes since 1945. Of the four percid forms originally present, the blue pike (Stizostedion vitreum glaucum) is presumed extinct, and the sauger (S. canadense) was commercially extinct by the 1950's. The walleye (S. v. vitreum) has remained stable in eastern Lake Erie but the highly productive stock of the western basin collapsed in the 1960's. Closure of the walleye fishery from 1970 to 1973, necessitated by mercury contamination, provided an opportunity for the development of an international management plan for restoration of the stock. An inter-agency Scientific Protocol Committee evaluated walleye dynamics and recommended management by quota beginning in 1976. Although quotas have been exceeded several times, the walleye stock responded well to limited exploitation, steadily increased, and expanded its range. Landings of the yellow perch (Perca flavescens) increased during the 1950's, but a steady decline in abundance, beginning in the early 1970's led to the formation in 1980 of another international inter-agency task group to recommend a basis for quota management. The short-term management recommendation, reported and accepted in 1986, was to reduce fishing effort by 20% by 1990. Both management schemes evolved when the resource agencies of the five jurisdictions (New York, Pennsylvania, Ohio, Michigan, and Ontario), in the two nations surrounding Lake Erie, perceived a need for the increased and improved management of a shared resource. They sought an international forum in which to develop strategies, appointed inter-agency scientific task groups to develop a basis for management recommendations, and adopted a quota management scheme. Each jurisdiction is responsible for the enforcement and allocation of its portion of the quota between user groups. Reports of catch, effort, and biological observations on stock performance are submitted annually to a standing technical committee charged with updating quotas.

Book chapter↗

USGS1989

Hydrological, morphometrical, and biological characteristics of the connecting rivers of the International Great Lakes: a review

The connecting channels of the Great Lakes are large rivers (1, 200-9, 900 m3 • s-1) with limited tributary drainage systems and relatively stable hydrology (about 2:1 ration of maximum to minimum flow). The rivers, from headwaters to outlet, are the St. Marys, St. Clair, Detroit, Niagara, and St. Lawrence. They share several characteristics with certain other large rivers: the fish stocks that historically congregated for spawning or feeding have been overfished, extensive channel modification have been made, and they have been used as a repository for domestic and industrial wastes and for hydroelectric energy generation. Levels of phosphorus, chlorophyll a, and particulate organic matter increase 3- to 5-fold from the St. Marys River to the St. Lawrence River. Biological communities dependent on nutrients in the water column, such as phytoplankton, periphyton, and zooplankton similarly increase progressively downstream through the system. The standing crop of emergent macrophytes is similar in all of the rivers, reflecting the relatively large nutrient pools in the sediments and atmosphere. Consequently, emergent macrophytes are an important source of organic matter (67% of total primary production) in the nutrient poor waters of the St. Marys River, whereas phytoplankton production dominates (76%) in the enriched St. Lawrence River. Submersed and emergent macrophytes and the associated periphyton are major producers of organic matter in the connecting channels. Another major source of organic matter (measured as ash free dry weight, AFDW) in the Detroit River is sewage, introduced at a rate of 26, 000 t per year. The production of benthos ranges from a low 5.4 g AFDW•m-2 in the Detroit River to a high of 15.5 g AFDW•m-2 in the St. Marys River. The rivers lack the organic transport from riparian sources upstream but receive large amounts of high quality phytoplankton and zooplankton from the Great Lakes.

Canadian Special Publication of Fisheries and Aqua↗

USGS1987

Meeting future information needs for Great Lakes fisheries management

Description of information needs for management of Great Lakes fisheries is complicated by recent changes in biology and management of the Great Lakes, development of new analytical methodologies, and a transition in management from a traditional unispecies approach to a multispecies/community approach. A number of general problems with the collection and management of data and information for fisheries management need to be addressed (i.e. spatial resolution, reliability, computerization and accessibility of data, design of sampling programs, standardization and coordination among agencies, and the need for periodic review of procedures). Problems with existing data collection programs include size selectivity and temporal trends in the efficiency of fishing gear, inadequate creel survey programs, bias in age estimation, lack of detailed sea lamprey ( Petromyzon marinus ) wounding data, and data requirements for analytical techniques that are underutilized by managers of Great Lakes fisheries. The transition to multispecies and community approaches to fisheries management will require policy decisions by the management agencies, adequate funding, and a commitment to develop programs for collection of appropriate data on a long-term basis.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1987

Dynamics of the recovery of the western Lake Erie walleye (Stizostedion vitreum vitreum) stock

After its 1957 collapse under intensive fishing and environmental stresses, the walleye (Stizostedion vitreum vitreum) stock of western Lake Erie remained low throughout the 1960s. A moratorium on both sport and commercial fishing, resulting from the 1970 discovery of mercury concentrations in walleye flesh, provided an opportunity for the development of an international interagency management plan. The quota management plan developed depended on sequential projection of the fishable stock on the basis of estimated annual recruitment and reports of total withdrawals from the stock. The fishery reopened gradually and quota management (including allocation among jurisdictions) was implemented in 1976. The stock, which had been gradually increasing as a result of relatively strong year-classes produced in 1970, 1972, and 1974, responded well to limited exploitation and produced a record year-class in 1977. Quotas were exceeded in 1978-80, but the stock continued to improve to the extent that the recommended rate of exploitation was increased in 1980 and again in 1981. As the population expanded, growth began to decline; the decline became apparent in young-of-the-year in the early 1970s and in older walleyes in the late 1970s. This trend toward progressively slower growth, which continued in the 1977 and subsequent year-classes, was accompanied by an increase in length at sexual maturity and a decrease in the percentage of female walleyes reaching sexual maturity at age III. As a net result of these changes, the proportion of mature females in the stock (an index of stock fecundity) decreased slightly during the interval 1975-84, while the estimated biomass of the standing stock rose from 9 000 to nearly 26 000 t. Both sport and commercial catches increased markedly after 1980 in Lake Erie's central basin.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1980

Minimum size limits for yellow perch (Perca flavescens) in western Lake Erie

During the 1960's yellow perch (Perca flavescens) of Lake Erie supported a commercial fishery that produced an average annual catch of 23 million pounds, as well as a modest sport fishery. Since 1969, the resource has seriously deteriorated. Commercial landings amounted to only 6 million pounds in 1976, and included proportionally more immature perch than in the 1960's. Moreover, no strong year classes were produced between 1965 and 1975. An interagency technical committee was appointed in 1975 by the Lake Erie Committee of the Great Lakes Fishery Commission to develop an interim management strategy that would provide for greater protection of perch in western Lake Erie, where declines have been the most severe. The committee first determined the age structure, growth and mortality rates, maturation schedule, and length-fecundity relationship for the population, and then applied Ricker-type equilibrium yield models to determine the effects of various minimum length limits on yield, production, average stock weight, potential egg deposition, and the Abrosov spawning frequency indicator (average number of spawning opportunities per female). The committee recommended increasing the minimum length limit of 5.0 inches to at least 8.5 inches. Theoretically, this change would increase the average stock weight by 36% and potential egg deposition by 44%, without significantly decreasing yield. Abrosov's spawning frequency indicator would rise from the existing 0.6 to about 1.2.

Technical Report↗

USGS1977

Establishment of white perch, Morone americana , in Lake Erie

White perch, Morone americana, was first reported in Lake Erie in 1953. No further reports of capture were recorded until 1973, when one fish was taken. Three other captures were confirmed in 1974, and 34 in 1975. All but 3 of the 38 specimens were taken in the warm, shallow western basin and the extreme eastern end of the central basin. The widespread distribution and the sizable numbers of specimens collected in 1975 strongly indicate that this nonendemic species has become established in Lake Erie.

Journal of the Fisheries Research Board of Canada↗