or Trinity Center during this study and is also an indication of 

 the depletion which selective fishing gear can exert on a population 

 despite presumably adeofuate escapement provisions made by law. In a 

 later study, Snyder (1931, p. 36) found that females predominated in 

 the gill-net oatohes at the mouth of Kalamath River. During the 

 years 1919-1923, inclusive, 63.2 percent of the catch consisted of 

 females* EQ.S records are based on oatohes from nets that allowed 

 the escapement of small fish, and, as he states, do not represent 

 a true cross section of the salmon population* Snyder points out 

 that a greater number of large males was taken in the fishery during 

 the latter part of the season^ but very seldom exceeded the nianber 

 of females* He also noted an increase in the size of the fish as 

 the fishing season progressed* 



After closure of the Klamath River to commercial fishing in 

 1933, the migrant adult population of salmon in Trinity River must have 

 returned to its original composition as regards sex ratios* Results 

 obtained during this study would certainly be more representative than 

 those of Snyder* In the vicinity of Lewiston, a sample of 33 fish con- 

 sisted of 1 female to 1*91 males in 1942 i a sample of 90 fish consisted 

 of 1 female to 2,33 males in 1944; and a sample of 116 fish consisted 

 of 1 female to 2.66 males in 1945 (Table 12), The ratio for all years 

 of record at Lewiston is 1 female to 2*4 males* At Trinity Center, 

 some 26 miles upstream from Lewiston, a sample of 548 fish examined in 

 1945 consisted of 1 female to 0*85 males, almost the reverse of the 

 ratios found at Lewiston. 



The difference in the sex ratios of fish sampled in these two areas 

 may be influenced to some extent by the Indian gill-net fishery at Hoopa* 

 The suraner and early fall runs of salmon that spawn near Lewiston must 

 pass nets that would take out many of the larger fish resulting in a 

 greater proportion of small precocious males in the upstream migration* 

 It has been observed on other streams, such as the Sacremento River, 

 that the sex ratio may change from year to year* Some investigators aver 

 that a preponderance of males, especially grilse, presages a large migra- 

 tion at maturity of the brood from irtiich the grilse were derived. 



Since the spring and summer salmon tend to spawn near Lewiston, and 

 those migrating later utilized the area near Trinity Center, the two 

 areas might be considered unrelated with respect to the composition of 

 their spawning populations. The sex ratio of the fish spawning in one 

 area is not necessarily related to that of the spawning population in 

 the other* In order to arrive at the sex ratio of all salmon migrating 

 up the Trinity River above North Fork, the sex composition of both of 

 these populations must be considered* An average sex ratio determined 

 from salmon taken at the center of each area should evaluate both popu- 

 lations equally and should be representative for the total spawning popu- 

 lation* The sex ratio derived in this manner is 1 female to 1*63 males* 



35 



