Ecology of a northern pike (Esox Iucius) population in a small, oligotrophic Lake : with comparisons to other northwestern Ontario populations

Abstract

The life history and population dynamics of the northern pike (Esox lucius) within Squeers Lake, Ontario were studied in order to provide information on pike found within oligotrophic lakes. Results clearly demonstrate the Squeers Lake northern pike population is relatively stable but small in size, has a very low production rate, exhibits rapid growth, an early age of maturity and an intermediate life span. The low availability of spawning (and to a lesser extent nursery) habitat apparently regulates population size. The rapid growth may be the result of abundant food, lack of serious competition for food resources and presence of favourable environmental conditions. Epilimnetic summer temperatures 16-21°C) within the main lake basin were very near optimal for "adult" pike (ie 18-20°C, Casselman, 1978), whereas summer temperatures within the Western Arm (which formed the main spawning and nursery area within the lake) were near optimum for young-of-the-year and yearling pike (ie 26°C, Hokansen et al 1973). To assess accuracy in age and growth assessment for the Squeers Lake northern pike population, the validity of using scales and cleithra was examined. The high percent frequency of agreement, low index of average error (Beamish and Fournier 1981) and index of precision (Chang 1982) indicate both scales and cleithra are equally suitable tissues for assigning age structure to Squeers Lake northern pike provided that marks interpreted as annuli are in fact annually formed. An examination of the accuracy of age estimates through the use of partly known aged fish (via iii tetracycline labelling and mark-recapture methods) confirmed that the checks identified on both aging tissues were in fact annuli. Cleithra, were, however, more accurate for northern pike > age 10. Therefore, when age estimates are required without killing the fish, the use of scales can be recommended provided that the population is relatively fast growing and precision levels between the two tissues do not exceed 5%. In order to further determine what factors may influence northern pike growth and population size, the influences of lake morphometry and chemistry on 14 northwestern Ontario populations (including Squeers Lake) were investigated. Northern pike populations found within deep-oligotrophic lakes exhibited low population densities, a superior growth rate, piscivory and were spawning and nursery habitat limited. Northern pike populations from meso-eutrophic lakes had much greater population densities, exhibited much poorer growth rates, were generally opportunistic predators and appeared to be food limited. Northern pike from mesotrophic and shallow-oligotrophic lakes exhibited intermediate population size and growth rates with the maximal individual size of fish from these populations approaching that of northern pike from deep-oligotrophic lakes. With the increased acceptance of individual lake management, a number of management alternatives are proposed.