MATHISEN: NUSHAGAK SOCKEYE SALMON FISHERY 



ment levels, althoiiofh they differ in completeness. 

 Naturally the best records have been assembled 

 duririg the last period, while the most incomplete 

 records exist from the middle period. The 

 escapement records are discussed in order of 

 completeness. 



THE PERIOD 1946-1966 



and escapement level, rather in the overall ratio 

 of catch to escapement over the entire jjeriod. 

 The average catch amounted to 1,183,485 sock- 

 eye salmon and the average escapement to 

 1,385,204 spawners. The ratio is almost one to 

 one; or on the average, a pair of spawners pro- 

 duced a progeny of four fish. In terms of fishing 

 mortality, the rate of exploitation has averaged 



The records for this period are complete in 

 the sense that escapement estimates were made 

 for all streams draining into Nushagak Bay 

 (Table 2). Estimates were based originally on 

 ground or aerial surveys. In 1953, the Wood 

 River escapement was estimated from tower 

 counts in the trunk stream. In 1958, this tech- 

 nique was adopted for assessment of the Igushik 

 escapement, and in 1959 for that of the Nuyakuk 

 River. From 1960 to 1964, tower counting was 

 conducted in the Snake River system and inau- 

 gurated in the Nushagak-Mulchatna River in 

 1966. Otherwise, escapement estimates were 

 made by the less reliable aerial survey. The 

 earlier estimates based on ground surveys all 

 have in common a much larger variance, but they 

 gain in consistency because of the fact that large- 

 ly the same personnel conducted spawning sur- 

 veys in all years, even after introduction of tower 

 counts (Gilbert, 1968). 



In the present context, we are not jjrimarily 

 interested in the year-by-year changes in catch 



THE PERIOD 1908-1919 



No total escapement estimates exist for this 

 period, except for the Wood River system where 

 a counting weir was operated from 1908 to 1919 

 with the exception of the 1914 season. Daily 

 counts and comments on weir building and main- 

 tenance are found in Reports of the Commis- 

 sioner of Fisheries for the years in question 

 (Table 4). 



On the assumption that the ratio of the Wood 

 River escapement to the total Nushagak escape- 

 ment was the same for the years 1908-1919 as 

 was observed during the period 1946-1966, when 

 estimates were available of the Wood River 

 escapement as well as of the total Nushagak 

 escapement, then this ratio can be used to esti- 

 mate the total Nushagak escapement for the 

 years 1908-1919 from the weir counts. 



The ratio of the total Nushagak escapement 

 to the Wood River escapement has been computed 

 in two ways from data in Table 2. The first ratio 



Table 4.— Total Nushagak escapement 1908-1919. 



Wood River 

 weir count 



Estimated 

 Nushagak 

 escapement 



Estimated 

 total run 



Escapement 



OS percent 



of total 



run 



Sources: Reports of the Commissioner of Fisheries for the fiscal years 1908 through 1919 and special papers. Government Printing Office, Washington, 

 D.C., 1910-1921. 



753 



