be related to the distance fish must travel to reach 

 the spawning ground and to the type of spawning 

 area they use. In general, it seems that sockeye 

 salmon with the greatest distances to travel occur 

 in the early part of the run, while those with the 

 shortest distances occur in the late part. This is 

 quite evident on the Fraser River and is reported 

 to occur also on the Copper River in central 

 Alaska. 2 



Segregation of spawning groups in time by the 

 type of spawning area utilized has been reported 

 in some systems. 



Barnaby (1944) found that fish occurring early 

 in the run populate all the spawning streams 

 entering Karluk Lake on Kodiak Island, whereas 

 most of those appearing late in the run use only 

 the larger streams and lake beaches. Tagging 

 studies on the Skeena River in British Columbia 

 (Fisheries Research Board of Canada, 1957) 

 indicate that sockeye salmon bound for the smaller 

 tributary streams of Babine Lake pass through the 

 fishery earlier than those bound for the outlet 

 spawning grounds. 



Seasonal timing may also be related to the age 

 of fish. Rounsefell (1958) presents evidence that 

 "the age of downstream migration has a negative 

 effect on the season of return. The 2-year mi- 

 grants run first, followed by the 3-, 4-, and finally 

 the 5-year migrants. 3 The ocean age, on the con- 

 trary, has a positive effect. The 4-ocean fish run 

 earliest, followed in succession by the 3-, 1-, and 

 0-ocean fish groups." 4 Similar changes in age 

 composition during the run were reported for the 

 Copper River by Thompson. 



Segregation of age groups of sockeye salmon by 

 lake system and by spawning grounds within a 

 lake system has also been reported in the litera- 

 ture. Although the 4 2 age group 6 dominates the 

 Fraser River run annually, three races — the 

 Chilko, Taseko, and Birkenhead — are character- 



1 Thompson, Seton H. The red salmon (Oncorhynchus nerka) ol Copper 

 River, Alaska. Bureau of Commercial Fisheries Biological Laboratory, 

 Auke Bay, Alaska. (Manuscript). 



' Refers to the age (figured from time of deposition of the egg) at which the 

 juvenile salmon migrates from fresh water to the sea. Thus, a 2-year migrant 

 is a fish that migrates to sea in its second year of life, a 3-year migrant in its 

 third year. 



' Refers to the number of winters spent in the ocean before the fish leturns 

 to fresh water to spawn. 



1 This method of designating the age of Pacific salmon was first introduced 

 by (iilbert and Rich (1927). The first number denotes the total age of the 

 fish (figured from time of egg deposition), and the subscript represents the 

 year of life that it migrated from fresh water to the sea. Thus, a 4: salmon. 

 called "four-two," refers to a fish that migrated to sea in its second year and 

 returned as an adult in its fourth year of life. 



462 



ized by a consistent contribution of the 5 3 age 

 group or "2-year-in-the-lake" fish (Henry, 1961). 

 Koo and Smith (1960) noted that various localities 

 in the Iliamna-Clark system of the Kvichak River 

 drainage in Bristol Bay (fig. 1) showed different 

 age compositions. They stated that this was clear 

 evidence of the segregation of subpopulations. 

 Segregation of spawning groups in time and by 

 age might also occur in the commercially important 

 sockeye salmon runs of other river systems of 

 Bristol Bay. 



Knowledge of segregation is basic to under- 

 standing the dynamics of sockeye salmon stocks. 

 Further, it would provide information essential in 

 designing studies to identify and determine the 

 abundance of populations in the fishery or in the 

 trunk stream before they disperse to the spawning 

 grounds. Finally, such knowledge would have 

 application in showing whether, and to what 

 extent, individual spawning populations could be 

 managed independently in the fishery and what 

 effect present and contemplated regulatory policies 

 could have on these populations. 



The purposes of this study were: (1) To deter- 

 mine the extent that major spawning populations 

 of Naknek sockeye salmon may be segregated by 

 time of occurrence in the run, (2) to determine by 

 age study the seasonal pattern of age distribution, 

 and (3) to determine age segregation on the spawn- 

 ing grounds. 



The Naknek River system is one of the major 

 producers of sockeye salmon in Bristol Bay (fig. 

 1). In some years the sockeye salmon run to the 

 Naknek system has exceeded that to the Kvichak 

 River system, which is generally the most pro- 



Figure 1. — Bristol Bay, showing locutions of principal 

 river systems and the Naknek-Kvichak fishing district. 



U.S. FISH AND WILDLIFE SERVICE 



