Is there mixing of American Plaice populations in the Flemish Pass?

Abstract

American plaice (Hippoglossoides platessoides) on the Grand Bank (Divisions 3LNO) and Flemish Cap (Div. 3M) are thought to represent separate populations. However, in the late 1980s and early 1990s there was a change in the distribution of American plaice in the region. They were found in the deep waters of the Flemish Pass and in addition, the Grand Bank population as a whole was found in deeper waters. This raises the possibility of mixing between the two populations, at least in the area of the Flemish Pass. The purpose of this study was to examine the distribution, size and maturation of American plaice in the Flemish pass to help determine if fish in that area are a mix of fish from the two adjacent populations or if the fish remain separated there. American plaice collected from the western (Div. 3L) and eastern (Div. 3M) sides of the Flemish Pass were clearly different in mean length-at-age and in their maturation, with fish from the eastern side being larger at age and females maturing at a smaller size than those from the western or Grand Bank side of the Flemish Pass. Further, American plaice were not collected in the deepest part of the Pass that was surveyed. Thus it seems that fish in the Flemish Pass area are not mixing but rather are separate groups.