FISHERY BLLI.ETIN: \0L. 69, NO. 4 



gear at Chignik, later supplemented with seines, 

 which today are the only gear operated. Gill- 

 netting never became effective at Chignik be- 

 cause of the clear water there and the narrow 

 channel. But as in the case of the Karluk fishery, 

 there has been a selection and domination of 

 certain races (Dahlberg, 1968). 



In three important sockeye-producing systems, 

 the historical development has been the same 

 and resulted in a continuous decline of return 

 per spawner. Dahlberg sees the cause as dif- 

 fei-ential fishing mortality on the Chignik Lake 

 and Black Lake races with an overfishing on the 

 latter ones. Rounsefell (1958) suspects the ef- 

 fect of predation and stabilization of predator 

 populations in the alisence of the former large 

 contrast between off and peak years as the prin- 

 cipal cause. The evidence presented for the 

 Nushagak fishery points to various effects of net 

 .selectivity as a major contributing factor. 

 Viewed by themselves, each of the presented e.\- 

 planations may appear i^lausible, but the almost 

 identical happenings in three unrelated systems 

 suggest that a common underlying cause also 

 may be operating. 



In all three cases the decline started two dec- 

 ades or so after large-scale commercial harvest 

 had been in operation. Provided the initial rate 

 of reproduction remained the same the spawning 

 stock or the potential egg dei)osition was suffi- 

 cient to maintain the runs, or rebuild them after 

 stringent regulations were put into effect. 



One might conclude that the primary produc- 

 tion of the nursery areas, which all are oligo- 

 trophic lakes in the three mentioned systems, 

 started a slow decline from the moment fishing 

 began, and the enrichment from salmon carcasses 

 was substantially reduced relative to the situ- 

 ation which pi'evailed prior to commercial 

 harvest. 



Clearly, a hypothesis of this type cannot be 

 demonstrated from the data presented. Rather, 

 conclusive evidence must be sought from other 

 sources. One is descriptive and involves a study 

 of the sedimentation rates in prefishing years 

 and in recent ones from bottom cores. Great 

 changes in basic lake productivity should bo re- 

 flected in the yearly sedimentation rate of diatom 

 shells. Donaldson (1967) has demonstrated 



that changes in escapement level are indicated 

 by phosphorus content of corresponding bottom 

 sediments. 



Experimental evidence on the role of the bio- 

 genic enrichment from salmon carcasses can be 

 obtained from a lake fertilization similar in con- 

 tent, volume, and mode of dispersion to that 

 ])rovided by the dying spawners themselves. 



ACKNOWLEDGMENTS 



The basic data for this paper were assembled 

 in 1961-1963 under Contract No. 14-17-0007-20 

 with the Bureau of Commercial Fisheries. The 

 author acknowledges with thanks a valuable re- 

 view of the manuscript by Dr. C. DiConstanzo 

 and many fruitful discussions with Dr. R. L. 

 Burgner, Director of the Fisheries Research In- 

 stitute, and with my colleagues, Drs. D. E. Rogers 

 and B. J. Rothschild. 



LITERATURE CITED 



Batts, B. S., and K. J. FiscnLER. 



1967. Historical data on the sockeye salmon runs 

 to NushaKak District, Bristol Bay, Alaska. Univ. 

 Wash., Fish. Res. Inst. Circ. 67-10, 6.3 p. 



Beverton, R. J. H., AND S. J. Holt. 



1957. On the dynamics of exploited fish populations. 



Fish Invest. Minist. Agric. Fish. Food (G. B.), 



Ser. II 19, 53.3 p. 

 Burgner, R. L. 



1964. .Age composition of Nushagak red salmon. 

 Univ. Wa.sh., Fish. Res. Inst. Circ. 219, 62 p. 



BtRGNER, R. L., C. J. niCoSTANZO, R. J. ELLIS, G. Y. 



Harry, .Jr., W. L. Hart.man, O. E. Kerns, Jr., 0. A. 

 Mathisen, and W. F. Royce. 



1969. Biological studies and estimates of optimum 

 escapements of sockeye salmon in the major river 

 systems in southwestern Alaska. U.S. Fish Wildl. 

 Serv., Fish. Bull. 67: 405-459. 

 Dahlberg, M. L. 



1968. Analysis of the d>Tiamics of sockeye salmon 

 returns to the Chignik Lakes, Alaska. Ph.D. 

 Thesis, Univ. Washington, Seattle, 337 p. 



Dixon, W. J. 



1965. Biomedical computer programs. Revised ed. 

 Univ. California, Los Angeles, 620 p. 



Donaldson, J. R. 



1967. The phosphorus budget of Iliamna Lake, 

 Alaska, as related to the cyclic abundance of sock- 

 eye salmon. Ph.D. Thesis, Univ. Washington, 

 Seattle, 141 p. 



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