Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

• Published in: Canadian journal of fisheries and aquatic sciences 1998-12, Vol.55 (12), p.2548-2561
• Main Authors: Swain, D P, Chouinard, G A, Morin, R, Drinkwater, K F
• Format: Article
• Language: English
• Subjects: Canada, St. Lawrence Gulf; Gadus morhua; Hippoglossoides platessoides
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-55-12-2548

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3 degree C in September and 374-426 m and 5.2-5.4 degree C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.Original Abstract: Nous avons compare les associations d'habitat de la morue franche (Gadus morhua) et de la plie canadienne (Hippoglossoides platessoides) dans le sud du golfe du Saint-Laurent entre la saison d'alimentation estivale sur le plateau Madelinien et la periode d'hivernage dans le detroit de Cabot. Les donnees utilisees a cette fin proviennent de releves au chalut de fond effectues en septembre 1993, 1994 et 1995 et en janvier 1994, 1995 et 1996. Les deux especes frequentaient en hiver des eaux beaucoup plus profondes et plus chaudes qu'en ete. Chez la morue, l'effet de l'age sur la repartition en fonction de la temperature s'inversait d'une saison a l'autre, les individus plus jeunes occupant des eaux plus chaudes que les poissons plus ages en ete, et des eaux plus froides en hiver. Chez cette espece, la selection de l'habitat en fonction de la temperature et de la profondeur etait dans l'ensemble statistiquement plus prononcee en septembre qu'en janvier. Le seuil de signific