GRAYLING OF GREBE LAKE 



311 



Temperature 

 (degrees F. ) 



5/21 5/28 UL 6/11 6/18 6/25 7/2 7/9 7/16 7/23 7/30 8/6 8/13 8/20 8/26 



Figure 4. — Average weekly water temperatures (hourly interpretations from thermograph records) for Hatchery Creek, 

 tributary of Grebe Lake, Yellowstone National Park, Wyo., during 1953 and 1954. 



of Potamogeton robinsii. Through this dense 

 cover grew scattered patches of another pond- 

 weed, Potamogeton amplifolius. 



Bottom fauna was sampled with an Ekman 

 dredge (6 ins. by 6 ins.). Standardized collections 

 with the equipment available were possible only 

 on bottom without a vegetative cover at depths 

 above 15 to 18 feet. Two of the samples were 

 collected in shallow areas less than 18 feet where 

 only vegetation was retained by the dredge. 

 The organisms were rinsed from the plants and 

 enumerated for (1) general type ami (2) relative 

 abundance (table 2). Twenty-three samples from 

 the open water of the lake were analyzed. 



Table 1. — Physical and chemical features of Grebe Lake on 

 Aug. r>, 1954 



Tendipedidae ( = Chironomidae) were the most 

 important bottom organisms at all depths, both 

 in numbers and by volume, (table 2). Forbes' 

 (1893) collections from Grebe Lake, taken before 

 fish had been introduced, included the following 

 forms: (from the bottom), Chironomous , Gam- 



485001 0-59-2 



marus, Pisidium, Diaptomus lintoni, Daphnia 

 clathrata, and Cyclops; (from inshore samples), 

 Gammarus, Allorehestes, Pisidium, Corisa, Physa, 

 Chironomous, Spongilla, Nephelis, Clepsine, 

 Ephemeridae, Odonata, and Haliplus. 



Table 2. — Qualitative analysis of bottom fauna from Grebe 

 Lake, 1952 



1 Each sample was arbitrarily the amount of vegetation which filled a 

 2-quart jar without packing. 



HISTORY OF FISH IN GREBE LAKE 



In 1907, 10 cans of eggs of rainbow trout (Salmo 

 gairdneri) were planted in Grebe Lake (annual 

 reports of Superintendents of the Yellowstone 

 National Park, 1908). In 1912, 300,000 fry of 

 cutthroat trout (Salmo clarki lewisi) from Yellow- 

 stone Lake were introduced (record cards in Chief 

 Ranger's Office, Yellowstone National Park). 

 Since that time the two salmonid species have 

 hybridized to such an extent that by 1952 no 

 fish were found which were definitely pure strains 



