Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 68-73. 



Water replacements and their significance to a fishery 



By H. B. Hachey 

 Chief Oceanographer, Canadian Joint Committee on Oceanography 



Summary — Attention has been directed to some of the major and more apparent effects that water 

 replacements may have on various fisheries. It has been indicated that such interchanges may be 

 responsible for the destruction of a fish population or the extension of others. The loss of larvae to 

 scallop and haddock areas has been considered as the result of movements of a water mass, and it is 

 suggested that the availability and catchability of certain species is effected by certain water replace- 

 ment phenomena. When consideration is given to the cycle of life in the sea, it will be quite evident 

 that many indirect effects may follow from these water replacements. While the processes of long- 

 term replacements are not too well understood, wind action is one of the more apparent major casual 

 factors in short-term replacements. 



INTRODUCTION 

 While the changing characteristics of a water mass, such as temperature and salinity, 

 are followed in detail in the study of a fishery, the replacement of one body of water by 

 another is a process which, generally, only attracts attention when the characteristics 

 of the water bodies concerned are in considerable contrast. 



Whether it be of the estuary, a coastal area, or the open ocean, the particles of a 

 water mass are never at rest, being subjected to the internal and external forces of 

 gravity, pressure, wind, tide and the Coriolis force. The resultant movements of the 

 water particles under these forces bring about the flushing of estuaries, the replacement 

 of water masses in a bay or coastal area, the removal of water masses from a fishing 

 bank, and the transportation of large masses of ocean water from one location to 

 another. 



The flushing of estuaries has been given considerable attention during recent years, 

 due to the need of considering the many problems of pollution. The principles derived 

 from such studies furnish an insight into the mechanism involved in the replacement 

 of waters in a comparatively small area, almost completely land-bound. In contrast, 

 and on an ocean-wide scale. Cooper (1954, 127), has called attention to the large 

 variations in the phosphate content and biological productivity of the English Channel 

 in the last thirty years. He seeks an explanation in the replacement processes involving 

 the replenishing of deep Atlantic water by potentially rich northern waters, these deep 

 Atlantic waters eventually upwelling to determine the nutrient supply of the coastal 

 waters of north-eastern Europe. 



Attention is directed herein to many of the direct consequences to a fishery of the 

 various processes of replacement. 



THE DESTRUCTION OF A FISHERY 

 BiGELOw and Welsh (1925) describe the disaster to the tilefish, which first came to 

 light in March, 1882, when multitudes of dead fish were observed floating on the 

 surface between the latitudes of Nantucket and Delaware Bay on the Atlantic coast. 

 The area of destruction was at least 170 miles long by 25 miles broad, and covered 

 the entire zone inhabited by the tilefish north of Delaware Bay. It is estimated that 



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