Shallow‐water tomography: Acoustic maps of the New England shelfbreak front

Winter flounders occur from Labrador to Georgia and yield large catches off southern New England. This paper relates their distribution and seasonal movements to environmental factors.In spring immature and mature flounders are alongshore with spawning fish concentrated in shallow water. During "summer", winter flounders leave the shore zone in areas where water temperatures rise above about 15 °C but not where bottom temperatures do not reach this level. This movement toward cooler water does not continue into depths at which temperature is below about 12 °C. Flounders return to the shore zone in fall after temperature decreases below 15 °C. These temperatures are well below the upper incipient lethal for flounders of about 26 °C.Flounders remaining alongshore in summer are distributed in depth according to size and maturity. Small, immature fish are in the shallowest water, the region of highest light intensity, immatures of medium size deeper, and mature fish in both regions. Under experimental conditions immature fish of medium size moved into shade at lower light intensities than either small immatures or large matures.North of Cape Cod flounders move deeper in "winter" as the shallow water becomes colder than the deeper. To the south spawning condition is reached earlier and mature flounders remain in shallow water during the cold-water period.Off southern New England a large, sustained fishery denotes a large population of flounders. In the Bay of Fundy and off the coast of Nova Scotia winter flounders are restricted to a narrow depth zone, and good exploratory catches there probably do not indicate large populations. In the broader shallow zones of the southern Gulf of St. Lawrence similar catches suggest a larger population. Exploitation will depend on increased efforts by small otter trawlers or possible development of marine sport fishing.

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

Contributions to Canadian Biology and Fisheries ◽

10.1139/f31-010 ◽

1931 ◽

Vol 6 (1) ◽

pp. 241-313 ◽

Cited By ~ 4

Author(s):

A. W. H. NEEDLER

Keyword(s):

New England ◽

Shallow Water ◽

North American ◽

Late Summer ◽

Water Area ◽

Early Summer ◽

Seasonal Migration ◽

Vertical Movements ◽

Shallow Water Area ◽

Nova Scotian

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.

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