Response of a Boreal Northern Pike (Esox lucius) Population to Lake Impoundment: Wupaw Bay, Southern Indian Lake, Manitoba

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Abstract
A population of northern pike (Esox lucius) in Wupaw Bay, Southern Indian Lake, Manitoba, was monitored for 1 yr prior to impoundment of the lake and for 5 yr after impoundment. Impoundment had a pronounced but transient effect on pike reproductive success. The abundance of young-of-the-year pike in 1977, the 1st yr following impoundment, was 4–10 times higher than in the following 3 yr. Flooded terrestrial vegetation was apparently conducive to pike reproductive success only in the 1st yr after inundation. A strong 1977 year-class was evident in gillnet catches 4 yr later. This year-class was slower growing and in poorer condition than other year-classes. The impoundment of Wupaw Bay had no discernible effect on the growth, condition, or mortality of the adult pike population, with the exception of changes ascribed to the presence of the large 1977 year-class. The growth of the adult pike population appeared to be limited by forage fish abundance, but variations in feeding on fish were largely unexplained and were probably due to natural variation. The year-to-year pattern of forage fish reproductive success could not be related to the timing of lake impoundment, but may have been related to summer water temperatures. Variations in feeding on invertebrates appeared to be due to postimpoundment increases in productivity, but these changes were insufficient to affect population parameters. Wupaw Bay surface area increased by only 9% as a result of lake impoundment, the smallest areal increase in the Southern Indian Lake reservoir. The influx of nutrients and flooded terrestrial vegetation was therefore much smaller than in other temperate reservoirs where increases in pike production have been observed.