Structure and management of an exploited population of Atlantic sturgeon (Acipenser oxyrinchus) in the St. Lawrence Estuary, Quebec, Canada

The Atlantic sturgeon (Acipenser oxyrinchus) has been exploited commercially in the upper estuary of the St. Lawrence River right up until the present day. Statistics on annual landings from 20 to 40 t between 1940 and 1966, and an almost total absence between 1967 and 1975, were followed by a significant capture increase, which reached 120 t in 1993. Analysis of captures has shown that the median age of sturgeon caught has gone down from 11 to 6 years-old in recent years, that the length of the fish (LF) varied between 50 cm and 170 cm, and that the last significant cohorts supporting the fishery come from 1982, 1986 and 1988. In 1994, 2% to 4% of captures were larger than 150 cm. No fish in reproductive state, even among the largest individuals, was observed among the captures. Since 1995, we have adopted various regulations in order to protect the largest sturgeons, and to reduce the annual landings to 60 t in 1998. Monitoring of captures, conducted in collaboration with commercial fishermen, has enabled us to measure the effects of these new fishing regulations, which include fishing effort control, reduction of the season, size limits for captures, and imposition of a quota. These measures have allowed us to partially reach our objective, since landings in 1997 were reduced to 66 t. The absence of sexually mature adults in captures has always raised the question as to their abundance and the areas which they use. Current studies are demonstrating that the sexually mature adults use the deepest parts of the estuary, sectors which are not exploited in a sustained way by fishermen. Studies are in progress to locate spawning grounds and early juvenile habitat. Exploitation of this population will continue to be closely monitored.