56 DEPARTMENT OF GAME AND FISHERIES No. 9 



to large boulders. These are evidently derived from the glacial deposits common 

 along the shore. At a depth of a little over 5 metres the silt disappears and at 

 8 metres depth the bottom is composed of clean sand. Between 8 and 12 metres 

 depth, the sandy bottom gives way to black, porous rock sometimes bare and 

 sometimes covered with a thin layer of sand. This type of bottom continues 

 to a depth of at least 32 metres. The bottom fauna is fairly abundant at a 

 depth of 5 metres, not so abundant at 8 metres and beyond the latter depth 

 only stray forms are found. 



During the normal drift of water, the most favourable environment for 

 the fish held in cages on the bottom was found to be at a depth of 8 metres. 

 In deeper water, mortality rates became progressively higher and they 

 were slightly higher at a depth of 5 metres. At 8 metres depth the 

 region of maximum copepod density is close to the bottom and there 

 is a considerable bottom fauna. The water is usually clear and cold. 

 It is deep enough to be free of most of the silvering movements found in shallower 

 water and a headland to the west protects the region from the sweeping currents 

 that make the bottom so inhospitable in deeper water. At 12 metres depth and 

 over, the bottom fauna is scarce and most of the copepods are to be found a 

 considerable distance above the bottom. At 5 metres depth food is abundant 

 but the water often becomes warm and turbid. 



During the east to west drift the mortality rate was lowest in deep water, 

 a depth of 20 metres providing the most favourable environment. Closer to 

 shore the water was warm and turbid and the food supply was reduced. At 

 20 metres depth the water was cool, the thermocline was close to the bottom 

 and a greater number of copepods had been forced into the deeper water. 



This investigation has indicated quite definitely the location of the best 

 environments for fish confined in cages on the bottom. If the fish were free to 

 move around, the range of suitable environment would be much greater. In 

 cages, they must wait for their food to come to them. If they were free, they 

 could follow the movements of the food supply and live in places where food 

 was not so limited. Fish that come from the hatchery in good condition do 

 not eat much during the first week after liberation. Daphnia are usually the 

 first choice of food but by the second week copepods have become the main 

 diet. Since copepods live in open water, lake trout fingerlings may live there 

 also. As has been pointed out, the open water experiments were not successful 

 because of mechanical difficulties. If these fish require the protection of a 

 quiet bottom, the 8-metre depth is the best place for them. 



It is recommended that under similar conditions to those found normally 

 in Lake Ontario at Port Bowmanville, lake trout fingerlings be liberated below 

 the thermocline in water about 8 metres deep. Under such conditions as 

 prevailed during the time of the east to west drift, it is recommended that they 

 be liberated close to the bottom in water about 20 metres deep. It might be 

 safe to combine these recommendations by advising that the fish be liberated 

 below the thermocline and close to the bottom. 



The investigation might be continued with profit along three lines. Trolling 

 might be done in the regions found by experiment to provide the most favourable 

 environment, in an attempt to find lake trout fingerlings and also to find out 

 what enemies live in these areas. A more complete survey of the movements 

 of the copepod fauna would be instructive. An investigation of the region just 

 above the bottom, in water whose depth was 5 metres or less, would add 

 considerably to the information at hand." 



