250 



BUIvLETIN OP THE BUREAU OF FISHERIES. 



Table 22. — Estimates for Quantity op Nannoplankton and Total Plankton in Three Finger 



Lakes in 1918. 



[NoTS. — Total plankton equals net plankton plus nannoplankton. Quantities are shown in kilograms of dry organic material 

 per square kilometer of surface and pounds per acre. Living material would weigh about lo times as much as is indicated 

 in the table.] 



BOTTOM FAUNA. 



Samples of the bottom at different depths were obtained in the three Finger Lakes 

 and also in Green Lake by means of an Ekman dredge. This mud was sifted through 

 a fine meshed net and the organisms found therein were enumerated. The dry weight 

 and the ash of four of these bottom forms were ascertained. The results of these dredge 

 hauls are shown in Table 23. The observations were far too few in number to give 

 anjrthing more than a fragmentary idea of the density of the bottom fauna, since only 

 two hauls each were made in Canandaigua and Cayuga Lakes and but fom- in Seneca 

 Lake; in addition to this they were taken only in the deeper water. Hundreds, or 

 better still, thousands of observations, covering the bottom of each lake in various places 

 from the shore line to the greatest depths and extending through the different seasons 

 of the year, would be necessary to give an adequate idea of the character and abun- 

 dance of their bottom fauna. 



Only four forms have been included in the table because they constituted by far the 

 greater portion of the material obtained. A few nematodes and an occasional ostracod 

 and bivalve mollusk were noted in the shallower depths, but they were not present in 

 sufficient numbers to obtain their weights. 



A few larvae of Protenthes were obtained in the 32 m. haul in Seneca Lake and in 

 the 45 m. haul in Green Lake, but these were the only instances in which this larva 

 was noted. 



Chironomid larvae were found in all of the hauls except the one made at 32 m. in 

 Seneca Lake. They were most abundant in Ca3niga Lake, where they constituted by 

 far the most numerous form at a depth of 113 m. In the other three lakes, however, 

 they formed only a minor element of the bottom population, both in numbers and 

 in bulk. Earlier in the season they were probably more numerous, because many had 

 undoubtedly transformed to the adult stage by the time these observations were made. 



In Canandaigua and Seneca Lakes the relict amphipod Pontoporeia was second in 

 importance, while it was third in Cayuga Lake and first in Green Lake. It was most 

 abundant at a depth of 45 m. in Green Lake, where it furnished the largest amount of 

 dry organic material that was found in any of the hauls, namely, about 8,214 kg./km.^ 

 or nearly 75 pounds per acre. 



Oligochaeta were found in all except one haul; that is, the one at 34 m. in Ca3aiga 

 Lake. In half of the hauls they furnished the greater portion of the organic material. 



