MATHISEN: NUSHAGAK SOCKEVE SALMON FISHERY 



lOOi 



Table 6. — Age composition in trap and gill net catches 

 in Nushagak, July 1 and 5, 1919. 



I   '  I   ' ' I 

 40 45 50 55 60 



Total length (cm)(ME-FT) 



65 



70 



Figure 4. — Instantaneous rate of fishing by centimeter 

 groups. 



sidered due to statistical variability introduced 

 by the rather small escapements in 1949 and 

 1950. It was further demonstrated by similar 

 calculations for recent years with exact catch 

 and escapement data that once the males become 

 vulnerable to the gear, the coefficient of catch- 

 ability increases only slightly from 2- to 3-ocean 

 fish. Whereas in the lower part of the selection 

 range, the curves are fairly similar for males 

 and females, the rate of fishing on 3-ocean fe- 

 males was several times that of 2-ocean females 

 based on the average lengths of these two groups 

 given by Mathisen et al. (1963). As a result, 

 in years when 2-ocean fish predominated in the 

 run, a large preponderance of females was pre- 

 sent in the escapement as in 1946, when there 

 were 68% males in the catch and only 35% males 

 in the escapement. In 1948, when there was a 

 predominance of 3-ocean fish, the corresponding 

 figures were 44% and 49%. 



The selective action of the gill nets on the 3- 

 ocean fish can be demonstrated further by com- 

 parison of age composition of gill net and trap 

 catches made in the same year (Table 6). The 

 traps can be considered nonselective and were 

 placed close to the upper boundary line of the 

 fishing area (Moser, 1902). Therefore, the age 

 composition of the trap catches can be used as 

 an estimate of the age composition of the escape- 

 ment. Whereas the 2- and 3-ocean fish were 

 present in about the same numbers, the catch 

 by 5%-inch gill nets contained more than five 

 times as many 3-ocean fish as 2-ocean fish. 



Source: Clark, Frances N. 1933. Red salmon in the Nushagak District 

 of Bristol Boy Alaska. (U.S. Bureau of Fisheries) Nafl. Mar. Fish. Serv., 

 Biol. Lab., Auke Bay, Alaska. (Unpublished manuscript.) 



ESTIMATED ESCAPEMENTS, 1925-1945 



When the calculations outlined above are ex- 

 ecuted, an estimated escapement for each of the 

 years from 1925 to 1945 is obtained (Table 7). 

 Two years, 1932 and 1938, were not included 

 in the computation of an average escapement 

 level since no length measurements were taken 

 in these years. No measui-ements were taken 

 in the fishery in 1931; instead, scales and mea- 

 surements were collected in the Wood River, 

 and this length-frequency distribution has been 



Table 7. — Calculated escapements and total runs in 

 Nushagak District, 1925-1945. 



Total 

 catch 



Total 

 escapement 



Estimated 

 total 

 rurt 



Escapement 

 as percent 

 of total run 



757 



