Changes in Percid Populations and Species Interactions in Lake Erie

Changes in the percid community of Lake Erie from 1915 to 1975 are delineated mainly from recently published material. Sauger (Stizostedion canadense), blue pike (S. vitreum glaucum), walleye (S. vitreum vitreum), and yellow perch (Perca ftavescens) are the percids which have been affected by exploitation, eutrophication and the presence and proliferation of colonizing fish species. Changes in habitat, fishing techniques and gear have also affected percid and nonpercid interactions.Yellow perch, presently the most abundant percid, have experienced irregularity in recruitment, lack of strong year-classes, and increased exploitation. The concern over the status of yellow perch and walleye has led to some important management initiatives. Improved regulation of exploitation and present efforts by United States and Canadian government agencies to improve Great Lakes water quality, are expected to improve the success for long-term maintenance of percids in Lake Erie. Key words: Percidae, populations, Lake Erie, habitat change, exploitation, management, Stizostedion vitreum vitreum, S. canadense, S. vitreum glaucum, Perca flavescens

Properties of Age Structure Models for Fish Populations

The behavior of a class of dynamic population models that can be described as a life table operating on a population with a stock recruit relation formed by the product of the egg production and a survival function was examined. A combination of analytical and simulation methods were used to find necessary conditions for the stability of equilibrium populations and the properties of fluctuations about the equilibrium. Regular oscillations that occurred in populations with an unstable equilibrium were of most interest and these were considered as possible causes of the regular fluctuations in populations of fish such as sockeye salmon, Oncorhynchus nerka, or blue pike, Stizostedion vitreum glaucum.

Contributions of Year-Classes of Blue Pike to the Commercial Fishery of Lake Erie, 1943–59

The blue pike (Stizostedion vitreum glaucum) contributed about 12.7 million lb annually to the commercial production of fish in Lake Erie in 1915–59. Production averaged about 27% of the total for all species; in some years it exceeded 50%. The catch fluctuated greatly and was featured by a series of seven "highs" and "lows" during the 45-year period. The landings ranged between 2 million and 26 million lb; periods of peak production were 5 to 9 years apart. A sharp decline in the catch started in 1957. The take of 79,000 lb in 1959 was the lowest on record to that time.Age and size compositions of the catch were determined from samples of blue pike taken from commercial landings in the fall, 1943–59. Peaks in production in that period were attributed to a few strong year-classes separated by several weak year-classes. Of the 20 year-classes represented in the samples, those of 1944 and 1949 were by far the strongest; together they contributed 42% (by weight) of the fall blue pike production in 1943–59. The strength of the 1939 and 1940 year-classes was moderate and the 1954 year-class was the last one of any importance. The other 15 year-classes were weak.The 1957–59 decline in production was accompanied by a marked increase in rate of growth. Blue pike in age-group III weighed nearly eight times more and were 7.7 inches longer in 1959 than in 1951. Landings after 1958 consisted of only a few large fish. The collapse of the fishery forced blue pike fishermen either to fish for less valuable species or to discontinue operation.