Winter geomorphological processes in the Sainte-Anne River (Québec) and their impact on the migratory behaviour of Atlantic tomcod (Microgadus tomcod)

Abstract

Knowledge of the migratory pattern of the Atlantic tomcod (Microgadus tomcod) towards its spawning site is scanty and controversial. This situation is partly a result of the fact that the migration takes place during winter, a period when it is difficult to investigate the relationships between flow dynamics, habitat and fish behaviour. The data reported in this paper suggest that channel morphology and flow dynamics, controlled both by the tidal regime and the ice cover, influence the migratory behaviour of the Atlantic tomcod population of the Sainte-Anne River (Sainte-Anne-de-La-Pérade, Québec). Measurements of channel morphology and flow velocity at low water indicate that the formation of ice cover in winter, combined with the presence of sand bars near the confluence of the Sainte-Anne with the Saint-Laurent River, causes a decrease in the cross-sectional area of the channel. This reduction in area is compensated for by an increase in flow velocity at the mouth of the river, where velocities larger than 30 cm/s were measured at low water. Underwater video observations of tomcod movements in the Sainte-Anne River indicate that such flow velocities limit access of upstream migrating fish to the spawning site. The data demonstrate that upstream fish migrants avoid the downstream flow velocities occurring during the falling tide and favour the short period of flow reversal associated with large rising tides in order to move upstream. © 1998 John Wiley & Sons, Ltd.