Table 9. — Average condition factor (K) of trout from Cabin Creek and Virginia Lake (test waters) 

 and Old Tom and Saltery Cove Creeks (control streams before spraying (1962) and after 

 1963-64) 



[Number of specimens in parentheses. Fork length was used to calculate k] 



EVALUATION OF EFFECTS OF SPRAYING 



Spraying had marked effects on aquatic 

 insects and on fish in the streams but had no 

 detectable effect on clams and plankton near 

 the stream mouths. 



Aquatic Insects 



The most dramatic effect of the 1963 spray- 

 ing was the immediate annihilation of aquatic 

 insects in the test streams. In the control 

 streams the abundance of insects followed the 

 normal seasonal changes. 



Sampling of drifting insects collected on 

 June 21, after spraying, (table 4) contained 

 more Ephemeroptera than Diptera--the 

 reverse of the relationin the prespray samples 

 from stones. This finding agrees with that of 

 Hoffman and Surber (1949), who reported 

 Ephemeroptera to be more susceptible to 

 DDT than the chironomid Diptera. The unex- 

 pectedly high ratio of Ephemeroptera to 

 Diptera in samples of drifting insects in nny 

 study may have been caused by the relative 

 sizes and shapes of the two kinds of insects. 

 The mayfly nymphs were larger than the 

 Diptera larvae and had longer appendages. 

 Many of the naayflies becanrie tangled in the 

 mesh, whereas many of the smaller Diptera 

 nnay have passed through. 



Repopulation of insects on the sample stones 

 in streams of the sprayed watersheds was 

 insignificant during the summer of 1963. 

 The only invertebrate observed during the first 

 month after spraying was the water mite. 

 About 1 mo. (month) after spraying I found 

 a few minute Ephenneroptera nymphs on stones 

 in both test streams and a beetle larva in 

 Virginia Creek. The first postspray observa- 

 tion of a stonefly in the test streams was on 

 August 4 in Cabin Creek. Two stoneflies 



were found on September 11 in Virginia 

 Creek. 



Further evidence of the slow recovery of 

 aquatic insects was shown by the stonaach con- 

 tents of rainbow trout from Cabin Creek in 

 July and August (table 1). Only a few mayflies 

 and aquatic Diptera were found in 1963, whereas 

 in 1962 and 1964 the mayflies and aquatic 

 Diptera were abundant. 



On the basis of experiments reported in 

 the literature, I expected the insect populations 

 in the Skowl Arm streams to recover by the 

 end of the summer of spraying, but they did 

 not. By June 1964, however, the numbers of 

 Diptera and Ephemeroptera on test stones 

 in Cabin and Virginia Creeks approached the 

 prespray levels. Repopulation nnay have re- 

 sulted from eggs deposited before spraying, 

 from eggs deposited after spraying by adult 

 insects from untreated areas, or from a high 

 survival of the progeny of a few individuals 

 that survived the spray. Because the species 

 of insects were not detern-iined, life history 

 information cannot help explain the rates of 

 recovery. 



Ide (1957) found that postspray abundance 

 of chironomid Diptera exceeded the normal 

 prespray levels, but this increase did not 

 occur in the test streams in my investigation. 



Fish 



No deaths of fish from DDT were observed 

 during this study, although adverse effects on 

 fish of higher concentrations of DDT have 

 been reported elsewhere. Brook trout 

 ( Salvelinus fontinalis) were killed after an 

 application of DDT at the rate of 4.47 to 6.7 

 kg. per hectare in Ontario (Langford, 1949); 

 several species of fish were killed by an 

 application of 1.12 kg. per hectare in Idaho 

 (Adams, Hanavan, Hosley, and Johnston, 1949); 



13 



