70 H. B. Hachey 



cycle of a period of about 225 years, which has presumably passed its maximum. It 

 must be stressed here that the expansion of the Greenland cod fishery is associated 

 with the extension of warmer Atlantic waters into more northerly latitudes, although 

 such an extension is probably associated with the climatic cycle. 



THE LOSS OF LARVAE 



Studies on the replacement of Bay of Fundy waters were initiated some years ago 

 (Hachey, 1934), and it became evident that the main factors involved in the replace- 

 ment of these waters were land drainage, wind, and tide. Other things being equal, 

 an excess of south-westerly winds favoured the retention of surface waters within the 

 Bay and thus nullified the normal dynamic tendency for surface outflow and renewal 

 of the waters at greater depths. Under such conditions a type of " closed circulation " 

 is set up within the Bay, as opposed to an " open circulation " when surface waters 

 are carried out of the Bay to be replaced by inflowing deeper waters. During the 

 summer months the " closed circulation " favours higher surface water temperatures, 

 and the surface temperatures, as well as the temperature gradient in the upper layer, 

 can be used as an indication of the type of circulation prevailing. Dickie (1955) has 

 made use of the temperature data for the Bay of Fundy to show that successful year 

 classes of scallop are produced in those years when the " closed circulation " prevails. 

 Not only do the warmer surface waters hasten development of the scallop larvae to 

 the setting stage, but the " closed circulation " favours the retention of the larvae 

 within the Bay where they settle and grow on suitable scallop bottom. Under the 

 " open circulation " system, as indicated by lowered surface temperatures, the larvae 

 are carried out of the Bay and are lost to the Bay of Fundy scallop fishery. 



The replacement of Bay of Fundy waters is not necessarily a regular progressive 

 process, even when the " open circulation " system prevails. Ketchum and Keen 

 (1953) have worked out various mean flushing times and exchange ratios for various 

 parts of the Bay of Fundy, and they point out that although their conclusions were 

 based upon the distribution of river water, the same exchanges may be expected for 

 any material or organism transported by the water. Ketchum and Keen calculated 

 an average flushing time of 74 days for that part of the Bay of Fundy between Cape 

 Chignecto and a line south of Grand Manan. Bailey (1953) has shown that within 

 the period October 6th, 1952, and November 2lst, 1952, the waters of the Bay of 

 Fundy were almost completely replaced, a replacement that only became apparent 

 when it was found that the salinity throughout a section had increased by more than 

 0'5%o within the period. It might be emphasized that within this period of forty- 

 six days (or less), practically all free-moving larvae in the surface layers would 

 have been carried out of the Bay of Fundy. So too would all free-swimming forms 

 which were feeding at random. The higher salinities as found on November 21st 

 indicate that the replacement involved the inward movement of waters originating 

 from sub-surface depths, and these waters would necessarily carry into the Bay 

 non-swimming forms, and free swimming forms which were feeding at random. 



According to Walford (1938) the survival of the eggs and larvae of the haddock 

 on Georges Bank is dependent on the variations in the current system in this area, 

 these variations being controlled to a large extent by winds (Bigelow, 1927, 857). 

 He suggests that the loss of the eggs and larval population in 1932, which occurred 

 some time after the first week of March, was due to the removal by currents. Similarly 



