. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. LAKES AND IMPOUNDMENTS I D 11*1 B Averts D dgoe M <I850 1060 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 Figure 17. Number of species introduced into Lake Michigan each decade. No fish per lOmin trow* 500 T. 1973 1074 1975 1976 1977 1979 1979 I960 1961 1982 1963 1964 1B8S 1966 1967 1968 1969 19. Figure 18. Abundance ofalewife in Lake Michigan, 1973-1990 (USFWS trawl data). By the
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. LAKES AND IMPOUNDMENTS I D 11*1 B Averts D dgoe M <I850 1060 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 Figure 17. Number of species introduced into Lake Michigan each decade. No fish per lOmin trow* 500 T. 1973 1074 1975 1976 1977 1979 1979 I960 1961 1982 1963 1964 1B8S 1966 1967 1968 1969 19. Figure 18. Abundance ofalewife in Lake Michigan, 1973-1990 (USFWS trawl data). By the early 1960s, however, effective sea lamprey controls were in place through a combination of physical and electrical barriers on spawning streams and the chemical control of the larvae in the stream bottoms. This allowed the reintroduction of native salmonids and also the stocking of non-native salmo- nids. The sea lamprey problem persists and must be kept in check continuously using the controls men- tioned above. Sea lampreys do occur in the Illinois waters of Lake Michigan but not in detrimental numbers. The wound- ing rate on lake trout examined in fall assessments by state agencies is used to determine abundance and trends in the sea lamprey population. The wounding rates in southern Lake Michigan have been low since the 1970s. Southern Lake Michigan has few tributary streams suitable for sea lamprey reproduction, so most sea lampreys appearing in Illinois waters travel down from the northern end of the lake. Alewives are native to the Atlantic Ocean and were probably native to Lake Ontario. They spread through- out the upper Great Lakes when canals and locks opened the lakes to shipping. Alewives were first noted in the Illinois waters of Lake Michigan in 1953, and young-of-the-year were first noticed in 1956 (Wells and McLain 1973). By the winter of 1956-1957, commercial fishing nets were clogging with alewives (Wells and McLain 1979). In the absence of sufficient large p
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