308 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Creaser and Greaser (1935) made a comparative 

 analysis of age and growth of the Michigan and 

 Montana varieties. Leonard (1939a, 1939b, 1940, 

 1949) recorded a number of observations in Michi- 

 gan on stocks transplanted from Montana. Miller 

 (1946), Rawson (1950), and Ward (1951) increased 

 our knowledge of the species by life-history studies 

 on the grayling in Canada. Wojcik (1955) also 

 made a life-history investigation of the grayling in 

 waters of interior Alaska. 



In Yellowstone National Park, Wyo., the gray- 

 ling occurred naturally in the Madison River and 

 its tributaries, upstream to major barriers such as 

 the Kepler Cascades on the Firehole River and 

 Gibbon Falls on the Gibbon River. Transplants 

 within the Park have produced varying results. 

 Both North and South Twin Lakes provide good 

 grayling fishing for small fish, but the population 

 depends on regular stocking because there is no 

 natural reproduction of the species. The most 

 successful introductions have been those in a series 

 of three lakes (Grebe, Ice, Wolf), formerly barren 

 of fish life, above Virginia Cascades on the Gibbon 

 River. Grebe and Wolf Lakes are a direct part of 

 the Gibbon River system which drains into the 

 Madison River, and Ice Lake is a few hundred 

 yards from the main river on a small tributary. A 

 fourth grayling lake, Cascade, lies close to the 

 other three but is in the drainage of the Yellow- 

 stone River. 



An alarming decline in numbers of the grayling 

 in Grebe Lake occurred in 1948 and 1949. To 

 rectify this, the National Park Service, responsible 

 for preserving and maintaining the present stock 

 of grayling in Yellowstone Park, believed that 

 technical management measures were necessary, 

 but basic biological data on the species and on 

 Grebe Lake were lacking. This study, under the 

 auspices of the U. S. Fish and Wildlife Service, was 

 aimed at providing a scientific basis for the man- 

 agement of the fisheries of Grebe Lake. 



I wish to thank Dr. Karl F. Lagler, Department 

 of Fisheries, University of Michigan, for guidance 

 during this study and for critically reviewing the 

 manuscript. Field research was supervised by 

 Dr. O. B. Cope, Chief of the Rocky Mountain 

 Sport Fishery Investigations; equipment and funds 

 were provided by the U. S. Fish and Wildlife 

 Service. 



ENVIRONMENT 



PHYSICAL CHARACTERS 



Grebe Lake lies at an elevation of approximately 

 8,000 feet on Solfatara Plateau near the center of 

 Yellowstone National Park. This 145-acre lake 

 is contained in a circular basin. The volcanic 

 sand bottom is overlain by a blanket of muck 

 (decomposed organic matter and silt) about 1 foot 

 thick. The prevailing westerly winds have formed, 

 through wave action, a narrow sandy beach on the 

 eastern side of the lake. A maximum depth of 

 32 feet was found near the southeast shore (fig. 1). 

 At the outlet, remnants of a beaver dam have 

 raised the water level about 1 foot and formed a 

 shallow curving arm 50 feet wide and 300 feet 

 long. 



Four major inlets enter Grebe Lake. These 

 quickly break up into many small, spring-fed 

 tributaries upstream from the lake. In addition, 

 seepage areas contribute their flow, particularly 

 during the moist spring and early summer. The 

 outlet (Gibbon River) flows to the west and 

 empties into Wolf Lake (42 acres) about 1 mile 

 downstream from Grebe Lake. From there the 

 stream travels 15 miles westerly to unite with the 

 Firehole River and form the Madison River. 

 Four miles below Wolf Lake a 50-foot cascade 

 prevents any fish below the barrier from entering 

 the waters above (the Grebe Lake system). 



Temperatures at the surface and on the bottom 

 of Grebe Lake were recorded continuously by a 

 Brown thermograph (fig. 2) placed near the deep- 

 est area in the lake. Spring overturn occurred 

 during 1953 on or about the third day after the 

 ice completely left the lake. By July 1 the lake 

 had stratified thermally. Maxima of average 

 weekly surface temperatures (hourly interpreta- 

 tions) were reached in 1953 and 1954 between 

 July 16 and 30 (fig. 3). Temperatures were still 

 increasing at the bottom when the thermograph 

 was removed from the lake on August 27, 1953. 



The highest daily temperatures were 65° F. 

 (at the 6-ft. level) on July 20, 1953, and 67° F. 

 (1-ft. level) on July 13, 1954. Daily surface 

 maxima occurred in the afternoons (between 1 : 00 

 and 5:00 p. m.) throughout the season. A 

 surface minimum of 41° F. was recorded May 12, 

 1953. The daily range never exceeded 3° F. 



