10 KEPOKT OF THE COMMISSIONER OF FISHERIES. 



the work been carried on as a commercial venture, but during the year 

 1908 the results were not so encouraging, probably because of a 

 change in the methods employed. The claire was kept closed during 

 the summer in the hope of retaining the oyster food developed during 

 the preceding season, but this change resulted in the production of a 

 large number of diatoms not available to the oysters, while reducing 

 the quantity of those which could be utilized. The result was of 

 value in indicating a procedure which must be avoided in the future. 



SPONGE-PLANTING EXPEKIMENTS. 



The experiments of the Bureau looking to the development of a 

 practical system of sponge culture have reached a stage where the 

 methods can be recommended for commercial purposes, sponges 6 

 inches and upward in diameter having been produced in four j^ears 

 from cuttings planted by inexpensive means. It is believed that the 

 system can be commercially employed with profit, and it provides an 

 insurance against the obliteration of a valuable industry should the 

 present unnecessarily destructive methods of fishing result in the 

 practical depletion of the natural beds. A report upon this work is 

 in preparation and will be published during the ensuing year. The 

 experiments will be continued with a view to the development of im- 

 proved methods and the acclimatization of various species in waters 

 to which they are not indigenous. 



TERRAPIN-REARING EXPERIMENTS. 



The work of devising a practicable method of rearing the diamond- 

 back terrapin has been carried on as usual on the Choptank River, 

 Maryland, but arrangements are being made to transfer the experi- 

 ments to Beaufort, N. C, where it is thought they can be more eco- 

 nomically conducted in connection with the laboratory at that place. 



LAKE STUDIES. 



In cooperation with the Geological Survey of Wisconsin, the 

 Bureau has been making studies of the biological and physical char- 

 acteristics of the many lakes of that State. An important feature of 

 this work has been the determination of the gaseous content of the 

 deeper waters, as a result of which it has been learned that there is a 

 deficiency in certain lakes which renders them incapable of support- 

 ing fish life in their greater depths. This discovery is important from 

 the standpoint of fish-culture, as it furnishes a hitherto unsuspected 

 reason for the failure of certain plants of lake trout and other species. 

 The investigations will be continued. 



At the request of persons living in the vicinity, investigations were 

 made into the causes leading to the extermination of fishes in Devils 

 Lake, North Dakota, and as a result of these the Bureau has been en- 

 abled to make practical suggestions for the reintroduction of food 

 species and to point out a source of ample supply. The results of the 

 work are of general utility in connection with the numerous alkaline 

 lakes of the West. 



During the summer of 1907 investigations were continued at Sebago 

 Lake, Maine, and in the fall studies were made of the mussel fauna 



