A STUDY OF TWIN LAKES, COLORADO. 



161 



were so few in number and covered such a brief jieriod of time each j-ear tliat they give 

 onl V a fragmentary notion of the phmkton life of the hikes. Likewise tiie \ertical haul 

 method is In- no lueans a satisfactory one and both of these factors must be taken into 

 considcnation in the results given below. The following table shows the number of 

 thousands of individuals per square meter of surface. With the exception of a few 

 figures for the rotifers, these nunihei-s are averages of either two or three hauls. 

 Th(^ rotifers were not counted in all the catches, so that in a few instances the 

 numlx'i's given for them represent only the individuals of a single catch. 



Qiiaiilifii of jihiiild07i in Tiriii Lnlrx, ns ^liuini hi/ xrries of vertiad lianh iliirniij mciimerx af 190:1 ami 1903. 

 [Averat?e number of t lousands of individuals per stiuare meter.] 



Sp.-(i.s. 



Auureit cnchlearis 



Auuri a aculeata 



Notholea longi^pina 



Triarttira lougi^;eta 



Polyarthra sp 



Asplanchna sp 



Diaptumus judayi 



Cyclops 



Nauplii 



Daphnia hyalina, young 



• and alult .' 



Daphnia hyalina, adult 



ITPPER LAKE. 



1902. 



July- 



August- 



July- 



2.7 

 14.0 

 10.7 

 30.0 



24.2 

 27.8 

 35.3 

 175. 5 



58.2 

 12.4 



34.' 



15. ( 



51.; 



14i.i 



48.; 



16.; 



5.3 



26. 



2.0 

 7.0 

 5.9 

 5.5 



33.8 

 22.5 

 101.8 

 104.0 



30.4 

 6.4 



August — 



9. 



107. 



33. 



201. 



96.; 

 21.1 



28. 



2.0 



31.2 

 30.0 

 3.8 

 5.3 

 77.7 

 47.1 

 84.0 



64.2 

 20.3 



LOWER LAKE. 



1903. 



August — July— August 



21. 



1.1 

 30.0 



9.6 

 .W.6 

 45.4 

 84.5 



28.2 

 12.2 



16. 



28. 



12.4 



30.4 

 1.0 

 2.7 

 13.9 

 62.6 

 .S5.0 

 ,51.3 



64.6 

 28.0 



DTSTKIliUTIOX. 



With respect to vertical distribution, Anurea cochlearis, Notholca Jongisphia, 

 and Axplanchna were contined almost exclusively to the upper 10 meters. Anurea 

 acidecita and Triarfhra hmgiseta were found almost entirely T)elow a depth of 10 

 meters, rarely occurring in the upper 10 meters. Pdlijurilirn was rather evenly 

 distributed throughout the entire depth of both lakes. 



There was no diurnal movement of I)iaptonnis^ ('yeIoj).<i, and NmipJii. Daphnhi 

 hxjalina showed a diurnal movement of half a meter in July and 1 meter in August. 



The phytoplankton, as stated above, composed a comparatively small portion of 

 the total plankton, and the few forms remained practically uniform in quantitv dur- 

 ing the two periods of these observations. The Crustacea made up by far the 

 greatest bulk of the total plankton. 



FISHES. 



Cato><f(im IIS comiiierKOuil Lacepede. Common Sucker; ^^'hite Sucker. 



This sucker is very abundant in the lakes. At times immense numbers wei'e 

 .seen swimming at the sui'face with the dorsal tin and a part of the back projecting 

 above the water. This habit was noted when the w;iter was quiet, either early in the 

 morning or in the evening. As food tish. the sucker does not stand very high in the 

 estimation of local fishermen, conse(|uently little attention is paid to it except as bait 

 for trout. A few are caught in Lake CJreek by means of grab hooks. Some of the 

 ti'out feed rather extensively on young suckers. 



B. B. F, 1906—11 



