Table 28. — Number ofsockeye salmon in each escapement and 

 mimber of smotts produced, by year of spawning, Naknek 

 system, 1951,-61 



0.5 1,0 1.5 20 2.5 3.0 



FISH IN PARENT ESCAPEMENT (MILLIONS) 



Figure 13. — Relations between numbers of smolts pro- 

 duced and number of sockeye salmon in parent es- 

 capement in the Naknek system for the escapements 

 in 1954-61. The number beside each point indicates 

 the escapement year. The dashed line indicates the 

 optimum escapement for each curve. R=number of 

 smolts in millions, and E^number in escapement in 

 millions. Curve A fitted to all points ; curve B fitted 

 to 1956-61 points (see text). 



Ricker-type reproduction curves have been 

 fitted to the smolt-escapement data from the 

 Naknek systems for the escapements of 1954-61 

 (fig. 13). Curve A was fitted to all points and 

 curve B to the escapements of 1956-61. Smolt 

 production from the 1954 and 1955 escapements 

 may have been underestimated by a substantial 

 amount (because of problems in establishing the 

 procedures for sampling smolts) . Curve B is as- 

 sumed, therefore, to describe the smolt-escape- 

 ment relation better. 



For the Naknek system., estimates of total 

 ocean mortality for sockeye salmon from 3 years 

 of smolt migration ranged from 77.6 to 95.2 per- 

 cent and averaged 83.5 percent. No attempt was 

 made to correct these estimates for the take of 

 salmon by the high seas fishery. 



The replacement line in figure 13 is straight — 

 it is based on the assumption that the average 

 total mortality (83.5 percent) applies to all 

 levels of smolt migrations ; i.e., ocean mortality 

 is largely independent of numbers of smolts. If 

 ocean mortality tended to increase with increas- 

 ing numbers of smolts in the seaward migra- 

 tions, the replacement line would not be straight 

 but would curve upward. Conversely, if ocean 

 mortality tended to decrease with increasing 

 numbers of smolts, the slope of the replacement 

 line would decrease toward the right. Not enough 

 information is available to determine the nature 

 of ocean mortality, and the safest assumption 

 seems to be that its effects are mostly independ- 

 ent of numbers of smolts entering the ocean. 



As indicated in figure 13, maximum yield to 

 the inshore fishery may be realized with escape- 

 ments ranging from 600,000 to 1 million spawn- 

 ers. If the high-seas catches of Naknek River 

 sockeye salmon were taken into account (i.e., if 

 they were included among the survivors), the 

 total ocean mortality would be lower, the slope of 

 the replacement line correspondingly less, and 

 the apparent optimum escapement range some- 

 what higher. Thus, we encounter a paradox. If 

 reproduction curves of the kind shown were used 

 to maximize the inshore catch, the total catch 

 (inshore plus high seas) would be less than is 

 biologically possible. 



Additional observations are required to define 

 more precisely the form of the smolt-escapement 

 relation and ocean mortality rate. 



Ugashik System 



Estimates of the numbers of smolts produced 

 in the Ugashik system are available each escape- 

 ment year, 1956-60 (table 29). These estimates 

 have been used to construct a figure showing the 

 .smolt-escapement relation for the system (fig. 

 14) . Escapements of fewer than one-half million 

 fish in 4 of the 5 years caused a crowding of 

 points at the lower end of the scale; interpreta- 

 tion of the form of the smolt-escapement relation 

 is, accordingly, difficult. Smolt production ap- 

 pears nevertheless to increase as the size of the 

 escapement increases. The greatest number of 

 smolts (31.6 million) was produced by the 

 greatest number of adults — 2.3 million spawners 

 in 1960. Because we lack observations on escape- 

 ments of intermediate size, the best that can be 

 determined is that target escapements for the 



442 



U.S. FISH AND WILDLIFE SERVICE 



