Water replacements and their significance to a fishery 69 



at least a billion and a half dead tilefish were sighted. There is evidence to indicate 

 that the destruction of this fishery was caused by a sudden temporary flooding of the 

 bottom by abnormally cold water. It has been shown that the tilefish of the Atlantic 

 coast occupies a very definite environment, for it lives only along the upper part of the 

 continental slope where the water temperatures are approximately 10" C, and never 

 ventures into the lower temperatures on the shoaling bottom nearer land. We have 

 in BiGELOW and Welsh's account of the disaster to the tilefish, a well-documented 

 record of the significance of a temporary incursion of waters of contrasting tempera- 

 ture, which in this case brought disaster to a fishery. 



On the basis of present knowledge, the source of the abnormally cold water 

 responsible for such a flooding is to be found to the eastward. A study of the slope 

 water off the Scotian Shelf (McLellan, et al, 1953), has shown that, between the 

 northern boundary of the slope water and the continental slope, there is found in 

 varying quantities a body of cold water, less than 0-0° C off" the Grand Banks, and 

 less than 4-0'' C east of Sable Island. The quantity of such water, acting as a cushion 

 between the slope water and the continental slope, decreases with westward progression 

 until the slope water generally makes contact with the continental slope to the west- 

 ward of Emerald Bank. Northerly and southerly migrations of the northern edge of 

 the slope water regime, and westerly progressions and easterly withdrawals of the 

 colder waters along the continental slope, provide the mechanism for producing 

 sharp and sudden changes in the water temperatures on the continental slope and over 

 the outer areas of the continental shelf. While the disaster to the tilefish was of major 

 import, and the westerly progression of cold water must have been greater than normal, 

 similar phenomena on a less spectacular scale have been noted in recent years. 



THE EXPANSION OF A FISHERY 



In contrast, both as to time and extent, to the temporary incursion of colder waters, 

 bringing about the destruction of a fishery over a limited area, is the historical record 

 of the expansion of the Greenland fishery in recent years with the strengthening of the 

 Atlantic influence in northern latitudes. 



Passing over earlier history, about 1820, cod were known to be present in enormous 

 quantities in West Greenland waters, as far north as Disko Bay (Jensen and Hansen, 

 1931). Thereafter, they were absent for a long period of years. Between 1845 and 1849, 

 cod were again plentiful in the Greenland area and then entirely disappeared. From 

 1917 there was a marked upward tendency in the fishery. The catch increased from 

 approximately 1,000 tons in 1925 to greater than 12,000 tons by 1945, and this fishery 

 has persisted to the present. In dealing with the state of the West Greenland Current 

 up to 1944, Dunbar (1946) points out that, by 1928, the waters for the west coast of 

 Greenland were considerably warmer than in the preceding period, and that the peak 

 warm year was reached within the period 1930-40. The increasing Atlantic influence 

 however was clearly evident in Latitude 72 N in 1942. A comparison of oceano- 

 graphic conditions in Hudson Bay and Hudson Strait, as observed in 1930, with those 

 of 1948 (Bailey and Hachey, 1951) has shown that the observed higher temperatures 

 and salinities of 1948 are indicative of the increasing Atlantic influence in northern 

 waters generally. A meteorological study of Sherbog (Dunbar, 1946), has suggested 

 that the warming of the Arctic and sub-Arctic regions from Greenland to Siberia, 

 which has taken place in recent years, is one manifestation of a large scale climatic 



