44 Roosevelt Wild Life Bulletin 



Lowering the water level will damage no construction work and only 

 slightly interfere with the winter use of the lake. There will be, of 

 course, still a large surface from which to harvest ice, the cost of 

 which will be only slightly increased by the greater distance over 

 which it will have to be carried. Xo harm will be done through the 

 loss of water, as the working level of the lake will be easily rees- 

 tablished by the spring thaws. There are some collateral advantages, 

 especially from the standpoint of mosquito control. The exposure 

 and freezing of the flats should operate to destroy some of the unde- 

 sirable vegetation. It would almost certainly destroy any larvae of 

 that very troublesome mosquito, Mansonia perturhans, living about 

 the lake. It would afford the best of opportunity for clearing up the 

 lake shores and removing obstructions, etc. 



" Some biological disadvantages must be noted. Various animals 

 associated with the leeches on the flats would suffer with them. 

 Doubtless large numbers of small frogs which abound in this lake and 

 which winter similarly to the leeches would be killed. However, their 

 lethal point to cold is somewhat lower than that of the leeches and 

 they penetrate the mud to a greater depth, so that the percentage of 

 mortalit}' might be expected to be lower. Other species of leeches 

 not included in the indictment against Macrobdella decora, such as 

 the large Hccmopis grandis, would be equally affected. jMany kinds 

 of aquatic insects, worms, mollusks, etc., which serve as food for 

 fishes would probably be killed. This important aspect of the matter 

 was discussed at length with Dr. Adams, our conclusions being that 

 too little is known of the winter condition of many of these organisms 

 upon which to base a positive decision. Especially do we know little 

 of the powers of resistance to cold of most specific organisms. The 

 only thing to do is to try the experiment, the value of which would be 

 very greatly enhanced were it possible to have a competent biologist 

 on the ground to observe the effects. In general it may be stated that 

 insects in their winter state are highly resistant to cold; that the 

 chironomids, whose larvae constitute perhaps the most important 

 single element in the food of small fishes, largely inhabit the aquatic 

 vegetation and the bottom ooze at greater depths than those aft'ected ; 

 and that the small entomostracan crustaceans, so important as food 

 for young fishes and many organisms on which the larger fishes sub- 

 sist, mostly produce winter eggs especially resistant to great cold and 

 drought. 



" It seems desirable to emphasize several considerations upon which 

 the success of the plan will depend, and the ignoring of which may 

 lead to its failure. It is very important that the water be not drawn 

 off before the leeches have become fully dormant. In that case they 

 would probably follow the receding water and take up winter quarters 

 at a new and safe level. For the same reason the level should be 

 reduced as rapidly as possible, and a time when much surface "vvater 

 is draining into the lake should be avoided. It is desirable that the 

 flats should be exposed during a cold snap so that freezing w411 take 

 place as rapidly as possible. If done during a warm sunshiny period 

 the leeches may be stimulated to burrow more deeply into the mud, 



