Life History and Ecology of American Plaice ( Hippoglossoides platessoides F.) in the Magdalen Shallows

• Published in: Journal of the Fisheries Research Board of Canada
• Main Author: Powles, P. M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1965
• Subjects: General Medicine; Magdalen; North Bay; George Bay; atlantic cod
• Online Access: http://dx.doi.org/10.1139/f65-050; http://www.nrcresearchpress.com/doi/pdf/10.1139/f65-050

Males reach marketable size (32 cm) at age 10, and females at age 8. Sexual maturity is attained at 25 cm (age 6) for males and 41 cm (age 10) for females, and maximum spawning occurs annually from mid April to mid May. Commercial fishing has reduced the number of year-classes in the fishery from about 26 in 1957 to 17 in 1961, but has not affected the rate of growth.The main summer fishery occurs in the Chaleur Bay, Shippegan Gully, and North Bay regions in depths of 40–100 m. In winter, American plaice were most abundant in depths of 180–460 m (bottom temperature 3–6 °C), although a few immatures remained in the cold inshore waters. In spring (April), plaice were taken mostly from 75 to 150 m depths (−1.0 to 5.0 °C).Adult plaice feed mainly on molluscs and echinoderms, and young plaice on polychaetes and small Crustacea. Feeding ceases almost completely during January–March. The main food competitor of plaice in the Magdalen Shallows is the Atlantic cod, which has the same general distribution during the summer. Atlantic cod, particularly those over 78 cm long, are also the main predators of small plaice, but mortality due to cod grazing has decreased in recent years because of declining numbers of large cod.Tagging and meristic studies indicate that Magdalen Shallows plaice are a discrete stock made up of two main groups. The groups are maintained by the tendency of plaice (excluding very old individuals) to return to the same areas each summer. The northern or "Miscou–Magdalen" group includes fish of Chaleur Bay, Shippegan Gully, and Orphan Bank regions. The southern or "Cape Breton" group occurs from George Bay to St. Paul Island.