Long-Term Cyclical Trends in Growth of Lake Whitefish in South Bay, Lake Huron

Abstract

A 39-year series of samples (1947–1985) was obtained with gill nets and trawls from a discrete population of lake whitefish Coregonus clupeaformis within the innermost basin of South Bay, Manitoulin Island, in northern Lake Huron. Back-calculations based on scales allowed growth in weight to be estimated for 47 year classes of lake whitefish. Growth of young fish prior to entry into exploited sizes was slow in the mid-1930s, increased to a maximum in the early 1950s, declined again to a minimum in the late 1960s, and increased again during the 1970s and early 1980s. Trend analyses with Fourier transformations provided cyclic sine wave models with a 32-year period that fit growth trends better (higher r2) than either linear or polynomial models. Long-term cycles in water level and temperature correlate significantly with the observed growth cycle. These two environmental factors account for 88% of the variation in lake whitefish growth, leaving 12% to be accounted for by community interactions. Based on observations in South Bay and fishery studies in other areas of the province, a hypothesis is suggested that long-term fluctuations in the hydrological cycle and other climatic factors interact to control long-term fluctuations in fish production throughout Ontario.