Some Effects of DDT on the Ecology of Salmon 

 Streams in Southeastern Alaska 



By 



ROGER J. REED,^ Fishery Biologist, 



Cooperative Fishery Unit, 



University of Massachusetts, 



Amherst, Mass. 01003 



ABSTRACT 



The effects on stream-dwelling fish and insects of an aerial application of DDT 

 (0.28 kg. (kilogram) per hectare or one-fourth pound per acre) to control black- 

 headed budworm were studied in four streams in southeastern Alaska. 



Prespray and postspray sampling was done to determine the food eaten by rain- 

 bow and cutthroat trout, the coefficient of condition of trout, the abundance of insects 

 on stones in the stream, the numbers of drifting insects, and the concentrations of 

 DDT in the water, fish, clams, and plankton. 



The effects of the DDT were an in-imediate marked increase in the number of 

 aquatic insects drifting in the stream the day of spraying and the annihilation of 

 aquatic insects within 3 days. No fish were observed to be harmed, although the con- 

 centrations of DDT and DDE (biological derivative of DDT) in their bodies increased. 

 The concentrations of DDT also increased in stream waters, plankton, and clams. 

 The one known long-term effect of the DDT on trout was a decline in their condition 

 factor, apparently due to the reduction in their food supply. 



The stream insects slowly began to reappear a few weeks after the spraying but 

 did not approach normal numbers until the following summer. 



The Forest Service, recognizing the po- 

 tential hazard of insecticide spraying, pro- 

 posed in I960 that a pilot study be undertaken 

 in Alaska to evaluate the effects on fish and 

 wildlife of the application of DDT in forested 

 watersheds. The Bureau of Commercial Fish- 

 eries agreed to undertake a 4-yr. (year) study 

 in cooperation with the Bureau of Sport Fish- 

 eries and Wildlife and the Alaska Department 

 of Fish and Game. 



This paper describes a study by the Bureau 

 of Commercial Fisheries to determine the 

 effects of DDT on insects and fish in two 

 Alaska salmon streams. The general plan 

 was to measure physical and biological fea- 

 tures in four streams--two test and two 

 control--before and after spraying with DDT 

 at the rate of 0.28 kg. per hectare (one-fourth 

 pound per acre). 



STUDY AREA 



Several criteria were used in selecting a 

 suitable study area: (1) The four streams 

 should be located near each other; 



^ The author made this study while employed at the Bureau of Commercial Fisheries Biological Laboratory, Auke Bay, 

 Alaska. 



INTRODUCTION 



Alaska is one of the last regions in North 

 America where insecticides have not been 

 used on a large scale. Although insecticides 

 have been used at Anchorage, Juneau, Fair- 

 banks, and some military installations in 

 other locations, they probably have affected 

 only limited areas. 



Most watersheds in southeastern Alaska 

 have valuable stands of Sitka spruce (Picea 

 sitchensis ) and western hemlock (Tsuga 

 heterophylla ) which are being cut by an ex- 

 panding timber industry. Many of these water- 

 sheds contain streams with significant popula- 

 tions of trout and salmon. 



The U.S. Forest Service and the forest 

 products industry have become concerned 

 about timber losses in southeastern Alaska 

 resulting from infestations of the black-headed 

 budworm ( Acleris variana ) and the hemlock 

 sawfly ( Neodiprion tsugae ). The Forest Serv- 

 ice has a program to locate areas of potential 

 epidemics of these insects and is considering 

 control methods. 



