THE MIGRATIONS OF HADDOCK AND THE INTERRELATIONSHIPS OF HADDOCK POPULATIONS IN NORTH AMERICAN WATERS

The haddock's range in North American waters is divided by the Fundian and Laurentian channels (both over 185 metres deep) into the "New England", "Nova Scotian" and "Newfoundland" regions. Marking experiments and comparisons of the age composition of stocks and of the growth rates show that there is practically no interchange between the first two. To the haddock, which are bottom-loving fish and never abundant below 185 metres (100 fathoms), the channels are barriers producing three divisions of the population corresponding to the divisions of the shallow water area. Seasonal migrations are shown in both the New England and Nova Scotian regions. Haddock withdraw in winter from areas north of Halifax and large haddock migrate into the gulf of St. Lawrence each summer. In midwinter the catches are chiefly below 70 metres (40 fathoms); in spring and early summer haddock appear well inshore in shallow water; in late summer they withdraw to deeper water; in late autumn they are caught in a great range of depths leaving the shallower parts as winter approaches. Both horizontal and vertical movements are correlated with temperatures—haddock avoiding those near 0 °C. and 11 °C. and preferring intermediate temperatures. Prior to maturity the haddock are relatively stationary becoming increasingly active in seasonal migration thereafter and changing their distribution—e.g., older haddock accumulate in the eastern part of the Nova Scotian region. The New England and Nova Scotian populations are groups of more or less distinct smaller units.