Reproduction and year-class strength of the Atlantic tomcod (Microgadus tomcod) in the Sainte-Anne River, at La Pérade, Quebec

Abstract

Experimental catches of a fyke-net fishery operated in the Sainte-Anne River during the 1980–1981 to 1983–1984 spawning seasons showed that although the majority of adult tomcod migrate upstream during rising tide, significant numbers do so against the tidal current. Most spawners return to the Saint Lawrence River during a falling tide. In the first 2 years, peak upstream migration occurred during the second half of December, and in the last 2 years, early in the second half of January. The date of peak upstream migration is significantly correlated with September and October air temperature in the summer habitat. Peak downstream migration of spawned-out adults occurred during the second half of January in 3 years and on 1 February in 1 year. The peak of the upstream and downstream migration of males and females generally occurred on the same dates. The spawning period extends minimally from mid-December to mid-February, but probably peaks close to the maximum of the downstream migration. The length and age composition of the Sainte-Anne River tomcod spawning stock remained relatively stable between the 1980–1981 and the 1983–1984 seasons. For the 1975–1976 to 1981–1982 period, the environmental variable to which year-class strength showed the highest parametric correlation was mean December Sainte-Anne River discharge. Stronger year-classes were produced in years of high water levels and discharge during the spawning period.