The effect of planting techniques and of predation on 

 survival of planted stock is receiving intensive study. 



SMALLMOUTH BASS UNIT 



Preliminary observations from a study in Greenleaf and 

 Opeongo Lakes suggest that spawning may not be as severe- 

 ly regulated by actual temperatures as by rates of change, 

 and that the thermal history of the eggs may be important 

 to the eventual survival of young bass and thus to year class 

 success. Important information on the influence of ex- 

 ploitation on the biology of smallmouth bass was obtained. 



WALLEYE UNIT 



In May and June, 1,200 walleye were tagged with large 

 numbered tags readable underwater. Studies by direct ob- 

 servation using Scuba gear were carried out. Density of fish 

 related indirectly to water transparency, maximum num- 

 bers being found where visibility was 13-16 feet. Evidence 

 indicated a schooling tendency which persists throughout 

 the year. Feeding activity was found to be closely related to 

 changing light intensity. 



Studies of the life history and ecology of successive 

 generations of splake have been made in natural condi- 

 tions to learn what to expect of these highly selected fish 

 when large plantings are made. 



PARASITOLOGY UNIT 



The parasite C/ugea hertwigi has infected 87 per cent of 

 smelt sampled in Lake Erie and has spread to Lake Ontario. 

 No evidence has yet been seen of it in Lake Huron. Work 

 on the manual of fish parasites for Ontario is proceeding 

 to the publication target date in 1971. 



PRODUCTIVITY UNIT 



This unit is developing a practical index that will allow the 

 classification of Ontario lakes in terms of their potential (or 

 producing pounds of fish. Total dissolved solids and mean 

 depth have been established as the two more important 

 indicators. 



DISCIPLINES UNITS 



LIMNOLOGY UNIT 



From May to October, 19 ponds and lakes within a 40-mile 

 radius of Toronto, of different origin, size, morphometry 

 and water supply, were sampled. Profiles were obtained of 

 temperature, dissolved oxygen concentration, specific con- 

 ductance, pH, total alkalinity, hardness and transparency. 

 Samples were also taken to be analyzed for phosphates, 

 nitrates and other chemicals. 



A study of higher aquatic plants was undertaken to (1) 

 find species or communities indicative of various stages of 

 eutrophication, (2) to determine the importance of these 

 plant communities as nurseries or feeding grounds for 

 young fish, and (3) to obtain information which may help 

 in deciding when aquatic growth should be controlled. 



SELECTIVE BREEDING UNIT 



Flotation testing of F3 hybrids (brook trout x lake trout) for 

 the 1967 year class was completed at Tarentorous, resulting 

 in 194 selected yearling brood stock. 



The first plantings of 30,000 yearlings from Ontario brood 

 stocks were made in Georgian Bay and South Bay in May. 



The brood stock at Chatsworth produced about one mil- 

 lion fertilized eggs which is sufficient to utilize present rear- 

 ing facilities. 



TECHNICAL STUDIES UNIT 



Recent emphasis given by several units to young-of-the- 

 year fish has increased the need for more specialized ser- 

 vice in identification and measurement of plankton, bottom 

 fauna and fish food organisms. 



A study to identify plankton species and populations, be- 

 fore and after operation of the Nanticoke Hydro develop- 

 ment, was initiated in co-operation with Fish and Wildlife 

 Branch, Hydro and Ontario Water Resources Commission. 



HARKNESS MEMORIAL LABORATORY 



The facilities were used by Brook Trout, Lake Trout, Lim- 

 nology, Parasitology, Selective Breeding, Productivity and 

 Smallmouth Bass Units, and by staff and graduate students 

 from the Universities of Toronto, York and Guelph and 

 Waterloo. 



SUBLIMNOS 



Within the Smallmouth Bass project, a program was initiated 

 to develop, stimulate and investigate the feasibility of 

 using advanced techniques of underwater habitation in 

 freshwater research. An underwater platform, called Sub- 

 limnos, was used in Little Dunk's Bay, from which was car- 

 ried out a bottom-sediment survey, population studies of 

 aquatic insect larvae, and testing and evaluation of under- 

 water sampling equipment. 



86 



