Research Document - 2010/052

Assessment of Habitat Quality and Habitat Use by the Extirped Striped Bass Population (Morone saxatilis) of the St. Lawrence Estuary, Quebec

By J. Robitaille

Abstract

This is a report on the knowledge of the habitats of the former striped bass population of the St. Lawrence, which disappeared in the late 1960s.

There is no information on spawning, incubation and larval life. Striped bass individuals from the former population with spawning size spent the winter in the upper Estuary and Lake Saint-Pierre. However, they seemed to have left these places when the water temperature should have triggered spawning.

Juveniles from the former population appeared in early July in fixed fishing gear installed on the foreshore. These small striped bass individuals were caught from early July at Neuville, then gradually at sites further downstream in August and September. The places where these juveniles were caught were in bays and coves sheltered from the current with various substrate conditions and most often near seagrass beds. Juvenile striped bass fed primarily on local food resources, especially invertebrates. These small individuals became more mobile as they grew and were reported in a larger number of sites in late summer. Most of the changes that may have affected the habitats of juvenile striped bass, between the disappearance of the former population and the reintroduction of the new one, were concentrated near Quebec City, between the Quebec Bridge and the Ile d’Orléans bridge; in other areas, habitat alterations were less extensive and were more punctual.

Striped bass individuals of one year and older did not appear associated with a habitat that could be characterized or defined in terms of particular physical-chemical characteristics. The best descriptors of their habitat would be the distribution and abundance of their preferred prey, i.e. crustaceans and soft-ray fish, especially clupeoid juveniles. One+ year-old individuals showed changes in their longitudinal distribution in the Estuary depending on their age and period of the year. Larger striped bass individuals (over 370 mm) had the largest seasonal movements. They frequented the lower Estuary, up to the Kamouraska area, during summer; as the colder season approached, they returned to the upper Estuary and Lake Saint-Pierre, a move that could be associated with reproduction. Habitat changes that occurred during dredging operations in the 1950s, seemed to have affected the summer distribution of immature individuals, exacerbating the effects of fishing. The dredging practices have improved since then, but the possible impacts on the new population must nevertheless be monitored.

Data on the population currently being recolonized indicate that natural reproduction has resumed in the St. Lawrence. It appears that the habitats required at each stage of the life cycle still exist. Priority should be given to locating breeding and early development sites in order to ensure their protection.

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