their parents (table 1). The odd-year line 

 continued to increase, and by 1941 the adults 

 were about nine times as abundant as they 

 had been in 1937. But the trend of increas- 

 ing numbers was reversed for progeny of the 

 escapements of 1941, 1943, and 1945; and the 

 escapement in 1947 was smaller than the 

 escapements before the increase began. For 

 the next five generations ( 1949-57) the escape- 

 ment of the odd-year line fluctuated between 

 1,000 and 9,000 fish. 



Then, the progeny of the fish that spawned 

 in 1957 were favored by an unusually good 

 fresh- water survival (21.7 percent) followed 

 by a relatively good marine survival (6.3 

 percent). The result was an elevenfold in- 

 crease in the escapement--from 2,800 in 

 1957 to 35,000 in 1959. From 1959 to 1965 

 the odd-year escapement fluctuated between 

 15,000 and 35,000. 



Recent History of the Even-Year Line of 

 Pink Salmon in Sashin Creek 



The abundance of pink salmon of the even- 

 year line in Sashin Creek parallels that of 

 the odd-year line from 1938 to 1946 (table 1), 

 but since 1948 abundance has been markedly 

 different in the two lines. The number of 

 adults of the even-year line began to increase 

 in 1938, and by 1942 about 92,000 were counted 

 into the creek. As with the odd-year line, 

 abundance of the progeny of this very large 

 escapement declined drastically; the escape- 

 ments dropped from 92,000 in 1942 to 4,000 in 

 1944 and only 900 in 1946. Unlike the odd-year 

 line, the even-year line never recovered; it 

 had fewer than 1,000 returning adults from 

 1946 through 1964. The continued failure of 

 the even-year line was due in part to re- 

 peated attempts to kill the few remaining 

 adults or fry in a study of straying (see 

 footnote 2, table 1 ). 



CHARACTERISTICS OF STUDY AREA 



Sashin Creek is about 4,000 m. long and 

 originates in a lake at 84 m. elevation. Less 

 than a third of the stream's length can be used 

 by salmon spawners because a waterfall about 

 1,200 m. from the head of tide prevents further 

 upstream migration. Only a few salmon spawn 

 in the narrow canyon that extends 300 m. 

 downstream from the waterfall or in the 

 intertidal zone because the gradient is steep 

 and the bottom is mostly bedrock. The main 

 spawning ground of Sashin Creek-- 

 13,629 m.2--lies between the intertidal zone 

 and the canyon. This study and all other recent 

 work concern a 13,084 m. 2 area of Sashin Creek 

 which is divided into three study sections-- 

 Upper (2,945 m. 2 ), Middle (4,067 m. 2 ), and 

 Lower (6,072 m.2). These three sections 



Table 2. — Size composition of bottom materials 1 

 and average gradient in three study sections 

 of Sashin Creek (McNeil, 1966) 



Section 



Average 

 gradient 



Bottom materials 

 composed of-- 



Cobbles 2 



Pebbles 

 and 



granules - 



Sands 

 and 



silts 4 



Percent Percent Percent Percent 



3 Pebbles and granules are 1.68 to 12.7 mm. 

 diameter. 



4 Sands and silts are <1.68 mm. diameter. 



contain 96 percent of the spawning ground 

 available to salmon in Sashin Creek. 



Several characteristics of the stream en- 

 vironment bearing on survival of pink salmon 

 and routinely determined in Sashin Creek are 

 bottom composition, oxygen content of the 

 intragravel water, streamflow, and precipita- 

 tion. 



Bottom Composition of Study Sections 



The size composition of the bottom mate- 

 rials varies with stream grade and is assumed 

 to change little from year to year. The Upper 

 section has a relatively steep gradient and 

 coarse materials in the bed; the Middle section 

 has an intermediate gradient and medium- 

 sized materials; and the Lower section has a 

 shallow gradient and fine materials (table 2). 



Daily Rainfall and Streamflow 



Although extremes in the flow of Sashin 

 Creek are dampened by the water storage 

 of several lakes and bogs in its watershed, 

 prolonged droughts result in low streamflows. 

 Rainfall is usually low at Sashin Creek during 

 July and August and markedly greater in 

 September (fig. 2). Changes in weather followed 

 the average trends in 1966 (fig. 2), and the 

 average streamflows had the same sequence-- 

 the average daily flow for each month was 

 lowest in July (0.92 c.m.s.); intermediate in 

 August (1.84 c.m.s.); and highest inSeptember 

 (3.47 c.m.s.). 



