Research Document 1997/66

Distributions of Atlantic cod and American plaice during the September 1996 survey of the southern Gulf of St. Lawrence and their relation to historical patterns

By Swain, D.P. and G.A. Poirier

Abstract

We described the distributions of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) in September 1996 using data from the annual bottom-trawl survey, and compared these distributions to those observed in earlier years. Catches of age-0 cod were less extensive than in 1995. The highest catches occurred in the area south of the Miramichi estuary. Age-1 cod were widely distributed in inshore areas between Miscou Island and western PEI. Catches of age-2 cod were sparse in 1996. Catches of age-3 and -4 cod were highest in shallow water off Miscou Island and northwest of the Magdalen Islands, and in deeper water southwest of St. Paul's Island. Densities of older cod were highest in a band extending from Chaleur Bay, through the Shediac Valley, north of PEI and throughout the northeastern region of the southern Gulf. Densities of age-5 cod in 1996 were relatively high in inshore areas of the western region and low over much of the central Magdalen Shallows. This resembled distributions in recent years (1993-1995) and during the low abundance period of the mid-1970s, and contrasted with distribution during the high abundance period in early 1980s. Even though conditions were cold in 1996, cod occupied relatively warm water in 1996, as they had in recent years and in the mid-1970s. This contrasts with the cold temperatures occupied by cod in the early 1980s, when conditions were warm but abundance was high. As in recent years, an unusually high proportion of cod occurred in eastern regions of the southern Gulf.

Distribution in 1996 was similar for small and large plaice, with one concentration in the central Shallows and a second in eastern regions of the southern Gulf. Plaice distribution in 1996 resembled that in 1994 and 1995, showing a marked eastward shift compared to plaice distributions in the 1970s and 1980s. Indications of the eastward shift were apparent as early as 1991-1993. Recent declines in plaice biomass have been confined to western strata of the survey.

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