Long term comparison of the population structure of the Cisco (Coregonus artidii le sueur) in smaller lakes
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Comparisons of the population structure of essentially non-exploited cisco populations in three Wisconsin lakes in 1981-82 with data from 1928-32 revealed that growth has increased significantly in all three lakes and that density appears to have declined since the 1930’s. The magnitude of the increase in growth in two of the lakes was comparable to the largest reported differences in growth among years within exploited cisco populations. This change in population structure is consistent with an explanation based on increased predation pressure from introduced piscivores, primarily walleye and muskellunge. Other possible contributing factors are discussed. Year class strength was variable and asynchronous among lakes both in the 1930’s and in the 1980’s. This persistent asynchrony among lakes supports Hile’s (1936) suggestion that variable year class strength of cisco depends primarily on local conditions within each lake; intraspecific competition may be a major factor.