TIME OF MIGRATION AND AGE GROUP STRUCTURE OF SOCKEYE 

 SALMON (ONCORHYNCHUS NERKA) SPAWNING POPULATIONS IN THE 

 NAKNEK RIVER SYSTEM, ALASKA » 



By Richard R. Straty, Fishery Biologist (Research) 

 Bureau of Commercial Fisheries Biological Laboratory, Auke Bay, Alaska 



ABSTRACT 



The annual sockeye salmon (Oncorhynchus nerka) 

 migration to the Naknek River system, Alaska, was 

 studied to determine to what extent major spawning, 

 populations were segregated by their time of occurrence 

 in the run. The extent of segregation by age in the run 

 and on the spawning grounds was also studied. 



Daily tagging on the Naknek River and subsequent tag 

 recovery on the spawning grounds showed that segrega- 

 tion of individual spawning populations by time of 

 occurrence in the Naknek run is limited. There was a 

 more or less complete intermingling of most spawning 



groups throughout the run; consequently, most spawn- 

 ing grounds derive their fish from all parts of the run 

 and, generally, in proportion to the size of the daily 

 escapement. 



Daily escapement age analysis indicated the lack of 

 marked segregation by age in the Naknek run. No 

 seasonal trend in age was apparent in the 1962 Naknek 

 run. 



Differences in age characteristics of major spawning 

 ground populations indicated segregation by age on the 

 spawning grounds of the Naknek River system. 



It is generally accepted that sockeye salmon 

 (Oncorhynchus nerka), when mature, return to the 

 river system of their origin to spawn. This 

 homing tendency was recognized as early as 1738 

 (Krasheninnkov, 1754) and given formal expres- 

 sion as the "home-stream" theory in the early 

 1900's (Chamberlain, 1907). Over a period of 

 many years, evidence in support of this theory 

 was obtained from marking experiments in 

 various river systems from Oregon to Alaska. 



The applicability of the "home-stream" theory 

 to individual spawning areas within a river 

 system was first suggested by Gilbert (1914-16, 

 1918-20) in his investigation of the sockeye salmon 

 of the Fraser River in British Columbia. He 

 found widely differing scale types on fish from 

 different parts of the Fraser River system. Sev- 



Note. — Approved for publication Oct. 7, 1964. 



' Based in part on a thesis submitted to the graduate school of the Uni- 

 versity of Hawaii, Honolulu, in partial fulfillment of the requirements for the 

 degree of Master of Science in Zoology, June 1963. 



eral areas were characterized by spawning popula- 

 tions having scale types so radically different as to 

 permit conclusive segregation of one spawning 

 population from another. Gilbert concluded that 

 the appearance in the fishery of fish with the differ- 

 ent scale types could be used to ascertain changes 

 in the racial composition of the catch. Since 

 Gilbert's early work, timing and duration of 

 abundance of various spawning groups have been 

 established by tagging experiments (Thompson, 

 1945; Killick, 1955), and racial identification has 

 been determined by scale studies (Clutter and 

 Whitesel, 1956; Henry, 1961). 



Studies on the Fraser River and several other 

 major sockeye salmon systems in North America 

 have shown that individual spawning populations 

 tend to be segregated in their time of occurrence in 

 the run. Each population appears to have its 

 own specific requirements for survival that 

 govern the time at which it migrates from the sea. 

 For a number of river systems this time seems to 



FISHERY BULLETIN: VOLUME 65, NO. 2 



461 



