1931 ANNUAL REPORT, 1930 33 



Provision for screening out fibrous materials, or filtering harmful substances, or 

 ponding in case of effluents containing harmful substances for the purpose of 

 precipitating them or aerating the efifluents, is recommended in each case where 

 necessary. It should be remembered, however, that the actual structure of such 

 devices or research along these lines is the work of mechanical engineers as well 

 as biologists. 



Under the direction and supervision of the Director of the Branch, the 

 majority of the field examinations were made by Mr. H. J. Dignan, B.A., 

 Instructor, Port Hope High School; and Mr. P. \V. Smith, M.S. formerly of the 

 Department of Botany, University of Toronto. 



Removal of Coarse Fish 



Numerous applications are received annually to remove coarse fish from 

 public waters, presumably with the idea of bringing about a more natural 

 balance between game fish and non-game fish, thus lessening food competition 

 to the advantage of the former. The attitude of the Fish Culture Branch towards 

 this subject is, in general, the same as that outlined in the preceding report of 

 the Department. The views of the Special Committee on the Game-Fish 

 Situation, 1928-30, coincide with the conceptions of the Department in this 

 respect. 



For a number of years the Department has authorized the removal of pike 

 (Esox lucius Linnaeus) from the Nipigon river for the purpose of giving the 

 native speckled trout, for which the river is famous, a better chance to survive. 

 Although the species in question may be protected in certain localities, its 

 removal from trout waters is amply justified. 



Gar pike {Lepidosteus osseus Linnaeus) and dogfish (Amia calva Linnaeus) are 

 of little value as food and are known to eat the more useful kinds. These are 

 subject to removal from game-fish waters. 



The removal of the carp and ling from game-fish waters, and their control in 

 all waters, is our objective. 



At the present time the carp has a definite commercial rating. In any 

 waters to which it has access it rapidly multiplies, particularly on account of its 

 excessive fecundity and rapid rate of growth. It competes with bass and other 

 game-fish varieties which subsist on insects to some extent. It is not of any 

 great importance as a forage fish, excepting in the fingerling stage, on account of 

 its rapid rate of growth. It has a habit of roiling the water in areas where it 

 dwells, and for this reason it is an unfavourable species in waters frequented by 

 clear-water-loving kinds, such as bass. For these reasons, it is highly undesir- 

 able. The spread of carp in inland waters and in the inshore waters of the Great 

 Lakes is a prelude to the use of implements of capture such as seines, which 

 wrought havoc to game-fish ; and means of preventing the introduction or increase 

 of carp in game-fish areas for this and other reasons cited, are adopted. 



The ling (Lota maculosa Le Sueur) is the only member of the cod family 

 found in fresh water. It is widely distributed throughout the Great Lakes and 

 in the larger lakes of Canada and of the northern states of the United States. 

 Its average weight is somewhere in the neighbourhood of from two to five pounds, 

 but specimens weighing ten pounds are not uncommon. It may be caught with 

 the usual implements of capture used for whitefish, herring, and lake trout, 

 such as gill nets, hooks, and pound nets. It very often does considerable damage 

 to fishermen's gill nets. 



