Plankton sampler, using both the No. 10 and 

 No. 20 silk bolting cloth plankton nets and cups 

 and a 3-liter Kemmerer water sampler. The 

 methods of collection, however, changed to 

 some extent during the study period. For 

 instance, the 1950 samples were collected by 

 oblique hauls with the No. 20 net Clarke- Bumpus 

 sampler only. In 1951 through July 23, sampling 

 was continued as in 1950. After that date, 

 oblique tows were made with the No. 10 net, 

 and, in addition, surface samples were collected 

 with the 3-liter Kemmerer bottle and strained 

 through the No. 20 net. The 1952 samples 

 were also collected with the 3-liter Kemmerer 

 bottle at each meter depth, surface through 

 6 meters. Samples from the various depths 

 were combined and poured through the No. 20 

 net. At the same time, oblique tows were made 

 with the No. 10 net Clarke-Bumpus sampler, 

 as in 1951. 



Since the 1957 study was concerned with 

 estimating the abundance of zooplankton, it 

 was decided to use the No. 10 net and cup with 

 the Clarke-Bumpus sampler. Ricker (1938a, 

 p. 22) states, "A mesh 20 net, used to take 

 several hauls in succession, decreases in 

 efficiency throughout the first few. The effi- 

 ciency of a mesh 20 net decreases with age." 



In contrast, concerning the No. 10 net Ricker 

 (1938a, p. 25) states,". . . (1) there appears 

 to be no change in its efficiency when a series 

 of as many as 20 hauls are taken in quick 

 succession, and (2) over a period of service 

 of a year and a half, no significant change 

 in efficiency occurred, although toward the 

 close of that period the trend appears to be 

 toward a slight reduction." For these reasons 

 the No. 10 silk bolting cloth net was selected 

 in preference to the No. 20 net, although 

 Ricker further observes that copepod nauplii, 

 small rotifers, and protozoa can to a varying 

 degree, depending on their size, pass through 

 the meshes of a No. 10 net. 



To achieve comparable data between oblique 

 hauls and Kemmerer bottle samples, it was 

 decided to strain all Kemmerer samples 

 through the No. 10 net. The water samples 

 from each meter depth were collected with 

 the 3-liter Kemmerer water sampler as in 

 the past. 



To increase the reliability of the Kemmerer 

 bottle samples and perhaps provide a check 

 on the reliability of the oblique haul quantitative 

 data, the size of samples taken with the Kem- 

 merer bottle was increased from 3 to 9 liters 

 at each meter depth. In addition, to obtain 

 depth distribution data, each meter depth 

 sample was kept separate. It was realized 

 at the time that the Kemmerer bottle samples 

 might not give reliable quantitative data be- 

 cause of the small sample size, the single 

 centrally located collection station, and the 

 possibility of avoidanceof the Kemmerer bottle 

 by active zooplankters. In practice an additional 

 unforeseen factor biased the quantitative data 

 collected by the Kemmerer bottle to an even 

 greater extent than those listed above. Because 

 of clogging, as the metered net collected 

 plankton, it became increasingly efficient at 

 collecting the smaller organisms that normally 

 would have passed through the meshes. This 

 gave the metered samples a higher and more 

 representative count of smaller organisms 

 than the Kemmerer bottle samples. Samples 

 were collected in the early afternoon each 

 sample day. 



Although there was a possibility of avoidance 

 of the Kemmerer bottle by some zooplankters, 

 it was assumed to be comparable for all 

 depths, as Bare Lake is shallow and unstrati- 

 fied. Hence, the Kemmerer samples should 

 yield qualitative and quantitative data for 

 interspecific comparison at all depths and 

 thus give valid vertical distribution data by 

 species. All of the Kemmerer samples were 

 collected at station 1 (fig. 2). 



The Clarke-Bumpus sampler was a non- 

 closing type, and hauls were made in the 

 following manner. As soon as the desired 

 towing speed was attained the plankton sampler 

 was allowed to enter the surface of the lake. 

 The sampler was lowered at a slow, uniform 

 rate until it arrived close to the bottom of 

 the lake and was retrieved at the same rate 

 so as to sample all depths uniformly. The 

 revolutions of the meter were recorded, the 

 sample transferred to a jar, and the net 

 thoroughly washed before the sampling meter 

 was taken to a different station. Nelson and 

 Edmondson (1955, p. 420) observed: "The 

 samples taken with a No. 10 net present no 



