16 U. S. BUREAU OF FISHERIES. 



The most abundant bottom inhabitants belonfy to three groups : (1) 

 Oligochseta; (2) Crustacea, represented by Ostracoda, Hyalella, and 

 Pontoporeia ; (3) Diptera larvae belonging to the genera Chironomus, 

 Tanypus, and Tanytarsus. 



Worms were most abundant in the deeper water — that is, from 

 about 35 down to 65 meters. A maximum of 6,800 individuals per 

 square meter of bottom was obtained in a catch from 64 meters. This 

 number would yield about 24 kilograms of dry material per hectare, 

 or 21 pounds per acre. The average number for the whole lake is 

 436 individuals per square meter, which is equivalent to about 1.4 

 kilograms of dry material per hectare, or 1.2 pounds per acre. The 

 ash amounted to approximately 10 per cent of the diy weight, and 

 86 per cent of the live weight consisted of water. 



The amphipod Hyalella was most abundant in the shallower water, 

 or in the 1-3 meter stratum. A maximum of 10,000 per square meter 

 was found in one sample taken at a depth of 1.75 meters. This max- 

 imum represented a weight of about 21 kilograms of dry material 

 per hectare, or 19 pounds per acre. The average number for the 

 entire area between the shore line and a depth of 10 meters is 900 

 individuals per square meter of bottom, representing about 3 kilo- 

 grams of dry material per hectare, or 2.6 pounds per acre. Approx- 

 imately 20 per cent of the dry weight consisted of ash. 



The amphipod Pontoporeia was found only in the deeper water, or 

 between 10 and 66 meters ; it was most abundant in the 30-60 meter 

 region. A sample from a depth of 47.5 meters gave a maximum of 

 13,000 individuals per square meter, while five other samples yielded 

 more than 9,000 per square meter. The maximum number repre- 

 sented about 64 kilograms of dry Pontoporeia material per hectare, 

 or 57 pounds per acre. The average number for all of the region be- 

 tween 10 and 66 meters is 2,100 individuals per square meter, equiv- 

 alent to 16.7 kilograms per hectare, or 15 pounds per acre, of dry ma- 

 terial. About 14 per cent of the dry weight consisted of ash and 77 

 per cent of the live weight of water. 



The snail population of Green Lake was found to be unusually 

 small, by no means large enough at the present time to account for 

 the large quantities of dead shells noted in the bottom samples taken 

 at depths of 5 to 15 meters. Two citizens who have lived in the 

 vicinity of Green Lake for many years reported that a large snail, 

 which they called a "limpet" (probably Campelartia integnim) ^ was 

 very abundant in the lake a number of years ago, but. at present this 

 snail is very scarce. 



A rather large mussel population was found in favorable places 

 where the water was half a meter to 3 meters deep. This popula- 

 tion consisted chiefly of Lavipsilis luteola. The average number of 

 the larger individuals was about 10 per square meter, while a maxi- 

 mum of 50 was noted in one locality. The maximum number repre- 

 sented a crop of about 18,000 kilograms per hectare live weight, 

 or approximately 16,000 pounds per acre. The average number 

 represented one-fifth as much, or 3,600 kilograms per hectare, or 3,200 

 pounds per acre. Substantially half of the live weight consisted of 

 shell, thus leaving 1,800 kilograms per hectare for the soft part or 

 body; an average of 91 per cent of the live body weight consisted of 

 water, leaving 162 kilograms per hectare, or 144 pounds per acre, as 



