After hatching, the young lampreys remain in a larval stage for 

 a period of about four years. Larval lampreys can be found buried in 

 sandy areas along the Trinity River at all times of the year. The 

 downstream migration of lamprey ammocoetes starts during the first fall 

 after hatching, at which time the smallest individuals are only 16 to 

 20 mm. (0.63 - 0.79 inch) long. These lampreys of the first age group 

 are too small to be retained by the l/4-inoh mesh fyke nets used to 

 sample downstream migrants of this and other species. Therefore, the 

 downstream migration of the first age group oould only be detected by 

 successive poisonings of ponds along the river's edge that were overflowed 

 during fall floods and then isolated by receding waters. These ponds were 

 poisoned with rotenone preceding flood periods to be certain that they were 

 devoid of all fish life. Following high-water periods and isolation from 

 the river, they were again posioned to obtain fish that had migrated during 

 the flood. In poisoned ponds lampreys would emerge fron the sand, swim 

 aroung in frenzied distress, and usually die in shallow water where they 

 were easily collected. Several thousand ammocoetes representing all age 

 classes were colledted from each of several sand bottom ponds 20 to 40 feet 

 in width and length following each flood period. It is very likely that 

 downstream movement of ammocoete stages is a passive movement. As silt 

 beds in irtiich these larvae live are destroyed or moved by high water, the 

 relatively helpless lamprey larvae are carried to new locations downstream. 



Fyke nets retained most young lampreys measuring 90 mm. (3.54 inches) 

 or longer. Ammocoetes appeared in fyke-net catches throughout the year, hut 

 larger catches were made during and following flood periods. Eyed lampreys 

 are also taken in fyke nets throughout the year. The relative absence of 

 eyed young in samples taken by poisoning would indicate that they make a 

 continuous eind deliberate movement toward the ocean. 



SAmON SPAWNING-BED SURVEYS 



Following a preliminary survey in 1944, two surveys were conducted 

 during the summer of 1945 to determine as nearly as possible the spawning 

 capacity of the Trinity River between the proposed Lewiston dam site and 

 North Fork at different flows. 



Nest Measurements 



During the 1945 spawning period, 20 completed nests were measured 

 (Table 16). These measurements included the entire area of gravel 

 disturbed by the spawning fish. Nest digging activities are somewhat 

 erratic, and salmon usually disturb a margin of gravel on each side of 

 the nest that is not actually a part of it. "Riere is also an area at 

 the downstream end of the nest which is covered by loose gravel carried 

 down by the current during nest digging and an area at the upper end where 

 gravel is loosened by the fish to cover the last eggs laid. Nest measurements 

 shows in Table 16 may be reduced by about 45 square feet to compensate for 

 these unused but disturbed areas (1-foot margin on sides and lower end of 

 nests and 2 -foot margin at the head), making an average nest area of about 

 63 square feet, equal to the nest size (9» x 7») established by rough 

 measurements in 1944* 



49 



