brook trout when no other fish are present in the lake. Brook trout are highly 

 vulnerable to competition by most other fish species, particularly by white suckers, 

 perch and rock bass. Other projects of the Brook Trout unit during 1965 

 continued the attempt to develop a classification for brook trout waters across the 

 province, and to explore the potential role of fish toxicants in brook trout manage- 

 ment. 



SMALLMOUTH BASS 



Smallmouth bass research continued to search for the explanation of the 

 relationship between average summer temperatures and bass year class strength. 

 In northern Ontario particularly warm summers consistently produce strong bass 

 year classes, and good bass angling three or four years later. It is important to 

 understand how this relationship operates in order to extend the range of appli- 

 cation of the principle across the Province. A study of the value of bass fingerling 

 stocking practices, in terms of angling benefits, is under way and will be completed 

 in these years. A new project to determine the sub-lethal effects of pollutants, 

 such as detergents, on bass was initiated during 1965. It is hoped that this project 

 will prepare the ground and develop some of the techniques necessary for a major 

 research programme in this field dealing with a number of our more important 

 fish species. Even low levels of detergent in the water were found to impair the 

 swimming ability of young bass. 



WALLEYE 



Walleye research is being directed away from the traditional "population" 

 approach and is concentrating on a basic study of walleye ecology using the direct 

 observation made possible by gear. It has already been found that light plays a 

 dominant role, even over water temperature, in determining walleye movement 

 and behaviour. They are found in different places and act quite differently on 

 bright days as opposed to cloudy days. Time of day and wind, with their relation- 

 ship to light penetration also affect distribution and behaviour. In this study some 

 800 walleyes were tagged with special tags which allowed identification of 

 individuals under water. A study of the Nipigon Bay walleye population was 

 completed during 1965. It was demonstrated that the recent disappearance of this 

 population was not caused by fishery pressure or by the sea lamprey. 



Other Research Programmes 



LIMNOLOGY 



The limnology research group continued to coordinate the limnological data 

 collections required by the several fisheries oriented research units. In addition, a 

 study of the thermal regime of South Bay was completed. This study has provided 

 a detailed description of the changes of temperature with depth and with season 

 for South Bay, which will be helpful to a number of fisheries research projects in 

 that area. A study of the zooplankton of South Bay was initiated. In Lake Ontario 

 a survey of the phytoplankton was completed in the Bay of Quinte. Analysis has 

 demonstrated the rapid rate at which this part of the lake is being changed by man. 

 The change is alarmingly fast and detrimental effects on traditional fish species are 

 already being observed. 



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