Seasonal growth and year class strength variations of perch near the northern limits of its distribution range
Abstract:The effects of temperature on seasonal growth and year class strength of perch Perca fluviatilis were studied in a subarctic lake in northern Finland. Two growth models, power and von Bertalanffy, were used to estimate the growth of perch during the growing season from 1988 to 1990. Air temperature, estimated as degree-days >10° C, significantly improved both model fits. The sum of degree-days also correlated positively with the year class strength of perch. The strongest year class was born in a warm summer 1988, while the 1987 year class was totally absent, which was due to the very cold summer of that year. The backcalculation of lengths of fish caught in 1990 showed that the overall growth of perch was slow in the cold summer of 1987 and relatively rapid in the warm summer of 1988. The subsequent growth of the abundant 1988 year class was rapid, even though the summers of 1991 and 1992 were relatively cool. The improved growth could be due to the lack of competition with previous weak year classes of 1986 and 1987. This observation suggests that density-dependent factors might affect growth even near the northern limits of the distribution range of perch.
Document Type: Regular Paper
Affiliations: 1: Department of Limnology and Environmental Protection, P. O. Box 65, Viikki, FIN-00014, University of Helsinki, Finland and 2: Värriö Subarctic Research Station, University of Helsinki, and Department of Biology, University of Oulu, P. O. Box 3000, FIN-90014, University of Oulu, Finland
Publication date: July 1, 2003