FORTY-SECOND BIENNIAL REPORT 



43 



One example of our long-range survey program is on the Tuolumne 

 River, where the Department of Fish and Game has undertaken a biologi- 

 cal study of the effects of the Modesto pollution on the Tuolumne River. 

 The objective of this study is to secure a sound basis of information on 

 which to evaluate the damage being done to this river and others of its 

 type by domestic and cannery pollution. The physical, chemical, and 

 biological characteristics of a 15-mile stretch of river above Modesto 



(TOP) Pacific lamprey, nine inches long, trapped in Fall Creek as it was descending to the 

 Klamath River, Siskiyou County. This is the so-called fresh water parasitic stage of this lamprey. 

 It is assumed that after the young lampreys emerge from the mud of the stream bed they undergo 

 a metamorphosis and enter the stage shown in this photo. They then attach themselves to almost 

 any fish that they can find and feed upon them until ready to go to the ocean. In the ocean they 

 continue to feed on marine fishes until ready to return to the streams to spawn and die. In the 

 Klamath River these lampreys are very serious predators on many species of fish, being particu- 

 larly noticeable on the king salmon. (BOTTOM) This nine-inch eastern brook trout was attacked 

 and killed when placed in a large experimental aquarium with several 10-inch lampreys. Note the 



three holes rasped in its side. 



