1088 



TJ. S. BUREAU OF FISHERIES 



and related physical problems. In all, 50 fixed stations were occu- 

 pied on the longer cruises, providino- records on about 270 series of 

 observations distributed through 4,435 statute miles traveled by 

 the vessel. 



Routine physical observations were carried out, such as sounding 

 for depth and for bottom samples, vertical and horizontal' distribu- 

 tion of temperature, rate and direction of the movements of water, 

 and determination of transparency. Chemical observations included 

 the determination of dissolved oxj'gen, carbon dioxide, total alka- 

 linity, and hydrogen-ion concentration, as well as occasional quanti- 

 tative determinations of other elements and compounds. Biological 

 observations included exact quantitative and qualitative determina- 

 tion of nanno-plankton and of the net plankton, and rough quanti- 

 tative and qualitative determinations of net pl'ankton, both vertically 

 and horizontally, and similar determinations for macro-plankton, 

 including young fish. Additional collections were made with seines 



FlGfRB 4 



S. Shearioater engaged in the cooperative survey of Lake Brie 



and trawls to determine the distribution and relative abundance 

 of young fish too large to be taken in plankton nets. 



The results of the survey having immediate practical value may 

 be summarized as follows: Physical observations established the 

 fact that in addition to the cold-water mass previously discovered 

 in the deeper eastern portion of the lake, a thermocline exists in the 

 shallow western portion, during a part of the year, covering the 

 greater part of the bottom of the lake with cold water. This thin 

 layer of cold water in the western part is broken up, however, by 

 late summer storms, and the deeper cold-water area varies materially 

 throughout the season in both extent and position. The movements 

 of the bottom cold-water mass are apparently governed by meteoro- 

 logical conditions, especially wind movements, and these in turn 

 produce rhythmic oscillations of the surface waters as well as major 

 displacements. Despite these considerable water movements, no cur- 

 rents were discovered that were strong enough to account for the 

 destruction of nets. 



