Ecology of northern pike, Esox lucius Linnaeus, in Savanne Lake, Ontario

Abstract

Important aspects of the life history and population dynamics of the northern pike, Esox lucius, in Savanne Lake, Ontario were studied during 1977 and 1978. Feeding relationships involving northern pike and walleyes, Stizostedion vitreum vitreum, and the initial impact of an open water sport fishery on these unexploited populations were also examined, Schumacher-Eschmeyer spring population estimates of 2,621 and 2,508 for 1977 and 1978, respectively, represented the mature northern pike population (ages 4-14 and greater than 45 cm in length) most vulnerable to the sampling gear. Adult northern pike did not appear to establish home ranges but moved throughout the lake during the year. A sex ratio of 1.19 females to every male was observed. Females were heavier than males at a given length and grew more rapidly at most ages. Fecundity estimates of 9,675 eggs per unit body-weight (kg) and an average of 20,081 eggs per mature pike were low for this species. Growth rates of Savanne Lake northern pike were slightly below average growth rates in Ontario and Minnesota waters and probably reflect the chemical characteristics of this lake, as well as the high density of piscivores relative to available food. Total mean biomass and annual production for age-groups 4-12 were estimated at 8,69 kg*ha[superscript-1] and 2,76 kg*ha[superscript-1]*yr[superscript-1] respectively, for the 1977-78 period. Low annual production was attributed to slow growth, low annual mortality, and the dominance of older age-groups in this unexploited population. Relative abundance and seasonal availability determined the incidence of prey consumed by adult northern pike and walleyes. Yellow perch (Perca flavescens) especially juveniles (60-110 mm in length), and shallow water ciscos (Coregonus artedii) predominated in observed annual diets of both species. Invertebrates, notably mayfly nymphs (Ephemeridae) and crayfish (Orconectes virilis), were of seasonal importance. Prey size was not a critical factor in determining predation, since the majority of examined northern pike and walleyes were capable of consuming far larger prey than were actually found in their stomachs. Northern pike appeared more vulnerable to angling than walleyes and comprised the greater portion of total angling yield for the open water study period. Catch per unit efforts of 0.88 fish per man-hour and 1.12 kg per man-hour for northern pike and 0.66 fish per man-hour and 0.48 kg per man-hour for walleye resulted from minimal angling pressure (1.24 hours per ha). Angling catches consisted primarily of northern pike, 50-70 cm in length and 5-7 years old, and walleyes, 40-50 cm in length and 6-10 years old, representing dominant age and size classes in the mature populations.