TEMPER ATVRE AND SPECIFIC (JRAVITY r.l7?7.4 770XS 37 



As Departure bay is somewhat northward of the direct flow of the river, light 

 southeast winds favour the influx of Fraser River water, while northwest winds hinder 

 its progress. In the summer the northwest winds are usually the strong winds and 

 hence their influence is commonly strongly marked. As the trend of Departure bay 

 is at a definite angle to the general trend of the coast, the wind in the bay is not 

 always in the same direction as the M'ind outside in the strait. Practically speaking, 

 the wind in the bay is always in one of two directions, either into the bay or out of 

 the bay. When the wind is blowing out of the bay the specific gravity of the surface 

 water may be greater than that of the strait near by; when it is blowing into the 

 bay the reverse may be the case or the difference may not be noticeable. 



An attempt was made to connect up the fluctuations in speciflc gravity with the 

 variations in barometer but the path of cyclonic centres varies so much in this 

 locality that it was impossible to trace any relationship, although the periodicity in 

 the fall and rise of specific gravity corresponds more or less regularly to the cyclonic 

 and anticyclonic periodicity. 



The effect of the Fraser river and the other large rivers of the mainland gradually 

 wanes after the height of the flood in late June until by the end of September it has 

 •practically disappeared as far as Departure bay is concerned. For a longer or shorter 

 time at this period the specific gravity is constantly high, before the winter fluctua- 

 tions begin. These winter fluctuations are largely dependent on the height of the 

 water in the local streams auji rivers and hence on the rainfall. The graph that has 

 been made for the precipitation, taking ten-day periods as in the other cases, shows 

 very definitely the relationship between the specific gravity of the water and the pre- 

 cipitation. 



In the daily readings fluctuations take place apart from the general rainfall effect, 

 and, as in the summer, this is largely due to the strength and direction of the wind. 

 A southeast wind may drive in fresh water from the Nanaimo river, to send the sur- 

 face specific gravity away down and in a few hours the wind may change to the north- 

 west and the wind blowing out of the bay may cause the specific gravity to rise again. 



As the time of greatest rainfall varies from year to year so does the time of 

 lowest specific gravity, but ordinarily the effect of winter rain is well over by the end 

 of March. Hence during April there is constant high specific gravity as during 

 October. In May the effect of the mainland rivers begin to show and the cycle is 

 complete. 



There is no doubt that the variations in time and degree of the various phases of 

 the cycle, both as to temperature and to specific gravity or salinity, have much to do 

 with the time of migrations of many, perhaps all, marine animals that come within 

 their influence, and the fuller the data on these factors, the more fully the migrations 

 may be explained. Data on migrations are accummnlating from year to year. A 

 paper was recently published calling attention to some points that have been observed^ 

 but in this paper attention was not directed to migration of fishes and from an 

 economic point of view, these are of the greatest importance. 



Although the conclusions from these records are very general, they are sufficient 

 to show what might be expected from more accurate and more extended work in the 

 same field. 



Summary. 



The temperature of the surface water in Departure bay is subject to much the 

 same fluctuations as the mean air temperature but does not go to the same extremes. 

 It is affected by influxes of fresh water, which tend to raise the temperature in the 

 summer and lower it in winter. 



The specific gravity is at its highest in the spring and in the fall. In the summer 

 it is lowered by the influx of water from the Fraser and other mainland rivers, being 



3 Fraser, C. M. Migration of marine animals. Trans. Royal Soc. Can., 191S. Sec. iv, p. 13'.^. 

 143. ' 



