Influence des régimes hydrologique et thermique de la rivière aux Pins (Québec) sur les migrations de fraie du Grand Brochet et sur l'avalaison des jeunes brochets de l'année

Abstract

The influence of the hydrological and thermal regimes of the Aux Pins River, a small tributary of the Saint-Lawrence River, on the spawning migrations of the northern pike (Esox lucius) and on the emigration of 0 + juveniles was investigated under natural conditions in 1975, and under controlled water level conditions in 1976. Factorial analyses were used to study the covariations between five biological variables and 12 hydrological and climatic variables. Approximately 70% of the adults were already present on the spawning grounds when the fyke nets were installed. Peak spawning occurred on 25 April in 1975 and on 9 April in 1976 (mean water temperatures: 7–10 °C). The emigration of adults occurred early in 1975. In 1976, downstream movements were very important immediately after spawning, regular but scarce when water levels were controlled, and important again at the end of the control period. Although they were modulated by high temperatures, the emigration of adults was stimulated by dropping water levels. Inversely, a rise in water levels, following precipitations, stimulated upstream migration, and slowed down the emigration movements, even late in the season. The first downstream migration of 0 + juvenile pike occurred approximately 30 days after peak spawning, at mean lengths of 19 mm. In late June 1975, 72% of the 0 + juveniles still remained in the Aux Pins River, as compared to 27% in 1976. The dropping of water levels at the end of the control period, in 1976, caused a massive emigration of 0 + juveniles. The authors' results can be used to predict the impact of water level manipulations, in a regulated spawning marsh, on the migrations of adult pike and of 0 + juveniles. © 1991 IFREMER-Gauthier-Villars.