ECOLOGICAL ASSESSMENT OF FACTORS AFFECTING WALLEYE OVA SURVIVAL IN THE LOWER FOX RIVER
Date
1986-10Author
Balcer, Mary D.
McCauley, Dennis J.
Niemi, Gerald J.
Brooke, Larry T.
Metadata
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The Fox River is a major tributary into Lake Michigan's Green Bay with an average discharge of 117 m3 sec-1 and an average gradient of 0.81 m km-1 in the last 62 km of the river (Epstein et al., 1974). Since the early l900's the river has been subjected to a high degree of urbanization and industrializatio.n The construction of power dams, locks and regularly main tained navigation channels coupled with the development of an industrial setting that includes 15 pulp and paper mills and 11 municipal sewage treat ment plants makes the Fox River one of the most densely developed industrial river basins in the world (WDNR 1978).
As.a result of industrialization, declining water quality is evident in the river. River biota has been adversely affected by rapidly increasing biological oxygen demand (BOD). zones of de-oxygenation and mats of paper fiber debris and bark (Patterson 1980). As early as 1924, fish die-offs were observed in the Lower Fox River near Green Bay. In 1925, the DePere Dam, DePere. WI was identified as a major factor blocking walleye migration upstrea,m thus forcing the fish to spawn on rip-rap areas below the dam (Bertrand et al.. 1976).
The construction and use of primary waste treatment facilities greatly
diminished fiber discharges into the river but did not significantly reduce BOD loadings to the lower Fox River. By 1967 the daily loading from indus trial discharges reached 142,900 kg day-l (Epstein et al.. 1974). In 1973 the daily BOD loading was still greater than 99 ,000 kg day-l (Weckwerth and Fenske 1982). even with the use of secondary waste. treatment facilities.
Recent compliance with the 1972 Federal Water Pollution Control Act has sig nificantly lowered the daily BOD load. In 1981 only 18,000 kg day-1 BOD was discharged into the river (Weckwerth and Fenske 1982).
While primary and secondary treatment of municipal and industrial wastes have led to improved BOD loadings and increased oxygen levels in the Lower Pox River, more serious problems affecting the river biota and man himself are still present. Discharge plumes containing ammonia levels
greater than the acute toxicity limit of fish of 1.5 mg L-1 NH3-N have been identified in the river (WDNR et al., 1983) . Between 1976 and 1977 a total
of 105 chlorinated and non-chlorinated organic compounds were identified from river biota, water, sediment and effluent discharges (WDNR 1978). Many of these chemicals are suspected of. having long term chronic toxicities, affecting fish growth (Warren 1972), causing off-flavor (Shumway 1968), bioaccumulating, and causing tissue damage (Fujiya 1961 and 1965).
Although acute toxicity to river biota has not been demonstrated in the Lower Fox River (Lien et al., 1985), chronic and latent toxicity have not yet been investigated. The effects of chemical discharges on fish migration, reproduction and the subsequent hatching and dispersal of young need to be addresse.d
The walleye, Stizostedion vitreum vitreum, is one of the major species of fish in the Lower Fox River. The walleye populations in the Fox River and southern Green Bay have historically been heavily exploited by man. From 1899 to 1946 the yearly production of walleye averaged 58 ,000 kg. A pro nounced production increase to 600,000 kg in 1950 was followed by a dramatic decline to 137,000 kg by 1952. After 1955, production continued to decline
steadily to only 5400 kg in 1970 (Becker 1983). Wells and McLain ( 1973) attributed this historical decline in the walleye fishery to over exploita tion and a deteriorating environment. They also noted that the generally low abundance since 1950 might logically be blamed on the unsuitable habitat in the heavily polluted area. Harris et al.,(1982) identified the Lower Fox River as the primary source for three of.the four critical stresses influen cing the Green Bay ecosystem (nutrients, suspended solids and toxic chemi cals). Although Colby et al., (1979) consider the walleye a true eurybiont, capable of tolerating a wide range of physical and chemical variability, they stress that under heavy exploitation, density-dependent factors lessen in importance and year class success becomes more and more dependent on abiotic factors within the watershed, (i.e. sedimentatio,n chemicals and
less than optimum spawning conditions.) Thus it would appear that both
exploitation of the fishery and deteriorating water quality in the Lower Fox River have contributed to the decline of walleye in this area.
In 1973, the Wisconsin DNR responded to slightly improved environmetnal
conditions of the Fox River and began a state sponsored stocking program to supplement the low population of walleye in the area. The Fox River received plantings of walleye fingerlings in 1977 and walleye fry in
1978 -1982 (Lychwick and Pellet 1982) . The Lower Fox River also received walleye fry in 1983 and 1984. A study to assess the Fox River walleye popu lation in the river was instituted by the Wisconsin D R in 1981 and conti nued into 1982. Results showed an estimated 60 ,000 walleye below the DePere Dam in the fall of 1981 and an estimated 12 ,000 in the area in the spring of 1982. Six year classes were present, representing primarily the five years
of fingerling/fry stocking (Lychwick and Pellet 1982).
Even though a large adult population had been established, natural walleye recruitment within the Lower Fox River appeared to have remained minimal, possibly because the rehabilitation of the fishery was accomplished before rehabilitation of the ecosystem. The abiotic elements were still suspected of interfering with natural reproduction and fry dispersal in the Lower Fox River.
In o der to more fully understand the effects of these abiotic factors on the successful reproduction of walleye in the Lower Fox River, the Uni versity of Wisconsin-Superior began a research project in 1985 (EPA Grant CR-811723-01-0). The goals of this project included:
1) Locating potential walleye spawning grounds in the Lower Fox River.
2) Determining the fitness of the spawning stock of walleye in the Lower Fox River.
3) Determining the amount and success of walleye spawning in the
river.
4) Developing appropriate in-situ incubators for walleye ova and uti fizing them to examine ova survival in selected are s of the river.
5) Determining the physical and chemical environment of developing ova and the effects of water quality on ova survival.
Subject
ecological assessment
walleye
Lower Fox River
ova survival