DISTRIBUTION OF COMMERCIAL FLATFISHES IN THE NEWFOUNDLAND-LABRADOR REGION OF THE CANADIAN NORTHWEST ATLANTIC AND CHANGES IN CERTAIN BIOLOGICAL PARAMETERS SINCE EXPLOITATION

The flatfishes of the Newfoundland-Labrador region are a very significant component of Canadian fishery resources and comprise four major species. They are: witch flounder (Glyptocephalus cynoglossus), American plaice (Hippoglossoides platessoides), Greenland halibut (Reinhardtius hippoglossoides), and yellowtail flounder (Limanda ferruginea). The fisheries for these species are made up of 11 separate management units, all under quota control with a total allowable catch in 1989 equalling 184 500 t for all stocks combined. Witch flounder is a relatively deep-water species, predominant at depths of 184 to 366 m and prefers temperatures in the range of 2.0-degrees-C to 6.0-degrees-C. It reaches its northern limits at Hamilton Bank, near southern Labrador, but is otherwise found throughout the southern range of the study area. American plaice is a more shallow-water species, preferring colder water. It is most abundant in depths of 90 to 250 m and bottom temperatures of -0.5-degrees-C to 2.5-degrees-C. While it is found throughout the whole study area, it is found in higher concentration on the tops of hard banks - particularly Hamilton Bank, the Grand Bank and St. Pierre Bank. The Greenland halibut is the deepest of the flatfishes, preferring depths of 500 to 1000 m and greater at temperatures of 0.0-degrees-C to 4.0-degrees-C. It is most abundant in areas north of the Grand Bank along the continental slope and deep channels running between the fishing banks. Yellowtail flounder, on the other hand, is the shallowest of the four species, preferring depths of 37 to 82 m where temperatures are in the range of 3.O-degrees-C to 5.0-degrees-C. The main area of significant abundance is on the southeastern Grand Bank known as the Southeast Shoal, although it is caught in a very small area of St. Pierre Bank. All species exhibit reductions in the age range of the respective populations since the beginning of commercial exploitation. As well, there have been increases in the growth rates and reductions in the age at maturity, with a few exceptions. These changes have generally been coincident with reduced population sizes although it was not possible to correlate analytically.