Water replacements and their significance to a fishery 71 



BiGELOW (1926, 77) wrote: " at the time of our March and April visits (to the north- 

 eastern part of Georges Bank) in 1920, the presence of newly spawned eggs in abund- 

 ance right out to the 1,000 metre contour proved that a drift out to sea was then taking 

 place from the southern point of the Bank." Walford (1938, 49) states: " there was 

 a very important difference between the circulatory picture in the season of 1932 

 and that of the corresponding period in 1931. While in 1931 the water movements 

 were such as to permit the bulk of the eggs to remain on the bank and hatch there, 

 in 1932 there were currents carrying eggs off the northern and southern edges into 

 deep water where they were probably lost to Georges Bank." In summary, Walford 

 (1938, 55) points out that a change in the circulatory system on Georges Bank may 

 be disastrous to the haddock brood, and consequently, may be an important cause of 

 fluctuations in abundance. 



Carruthers, et a/. (1951) have directed attention to the variations in brood strength 

 in the North Sea haddock in the light of relevant wind conditions, and the results of 

 these studies have directed considerable effort to the analysis of wind systems as 

 related to other North Sea Fisheries. 



AVAILABILITY OF THE FISH 



The displacement of surface waters on a grand scale by wind is amply demonstrated 

 by the great ocean currents of the North Atlantic, and the fundamental principles 

 have been thoroughly outlined in the classical work of Ekman (Sverdrup, et al., 

 1942, 492). Ekman has shown on a theoretical basis that a surface current set up by 

 wind is directed 45° to the right of the wind direction in the northern hemisphere, 

 and this has been shown by observation to be a satisfactory approximation in deep 

 water. In shallow water the deflection of the surface wind current is smaller. A wind 

 blowing parallel to a coast is thus effective in transporting surface waters towards the 

 coast, when the coast is to the right of the wind (cum sole from the wind direction) in 

 the northern hemisphere, and away from the coast when the coast is to the left of the 

 wind. 



The capture of young herring along the open coasts of the Bay of Fundy and the 

 Gulf of Maine is chiefly dependent upon fixed shore weirs. Huntsman (1934) states: 

 " that the herring are to a considerable extent quite near the surface during the 

 twenty-four hours of the day is not only a matter of direct observation, but a requisite 

 for successful operation of the weirs." Huntsman also states (1934, 96) that '* the 

 herring may be treated as a planktonic form ". It then becomes evident that herring 

 in the surface waters, and considered as a planktonic form, will be moved on or ofl the 

 shore with the varying direction of the wind. This is particularly pertinent on an 

 open coast, such as that of Maine, and the south coast of New Brunswick, where the 

 availability of the herring to the shore-fixed weirs must be determined in part by the 

 varying strength of the prevailing south-west winds during the summer months. 



TEMPORARY ADJUSTMENTS IN A FISHERY 

 Large scale water replacements of a temporary nature sometimes bring about 

 sharp and sudden changes in water temperature, the changes in environment being 

 sufficient to cause a body offish to either: 



(a) move away from a fishing ground, or 



(b) cease feeding and thus fail to be attracted to the bait. 



