FISHERY BULLETIN: VOL. 70, NO. I 



size of coho salmon smolts. These life history 

 features of Karluk coho salmon are compared 

 with those reported for various coho salmon 

 stocks from other areas on both the Asiatic and 

 North American sides of the Pacific Ocean. In 

 addition, the effect of a prolonged juvenile fresh- 

 water residence, a feature unique to the Karluk 

 system, on freshwater and marine survival is 

 discussed. All of the data on Karluk coho salmon 

 were collected incidentally during studies of 

 sockeye salmon. 0. nerka, the dominant salmon 

 species in the Karluk system; much of the in- 

 formation on other Alaska stocks is from un- 

 published administrative and progress reports. 

 Because I intend to discuss differences between 

 coho salmon in the Karluk system and those in 

 other areas, a description of general features of 

 the life cycle of coho salmon stocks is appropri- 

 ate. Typically, the adults enter streams and 

 rivers from late summer to November and spawn 

 in late fall and early winter. Some Asiatic 

 stocks, however, spawn as late as mid-March 

 (Smirnov, 1960). The progeny emerge as fry 

 in the spring following spawning and reside in 

 rivers or lakes for 1 or 2 years before going to 

 sea as smolts. In some areas the seaward smolt 

 migration begins in late winter (Chapman, 1961; 

 Smoker, 1953), but in most areas it takes place 

 from April to August (Godfrey, 1965). The 

 salmon grow rapidly in the ocean, and the adults 

 return to the streams and rivers to spawn 12 

 to 18 months later. However, a significant per- 

 centage of male coho salmon, particularly in 

 their southern range of distribution in North 

 America (California), mature precociously (6 

 to 9 months after they enter salt water) and 

 return to spawn the same year that they mi- 

 grated to sea (Shapovalov and Taft, 1954). 

 These fish are known as jack salmon. 



METHODS 



The data for adult coho salmon of the Karluk 

 system were obtained from fish from the 1966 

 escapement that were captured at the adult 

 counting weir or caught by sport fishermen at 

 the outlet of Karluk Lake about 300 yards up- 

 stream from the weir site. All fish were mea- 

 sured for length (mideye to fork of tail) with a 



caliper to the nearest millimeter. Mideye-fork 

 length was used because of morphological 

 changes that occur as the fish matures, partic- 

 ularly the elongation of the snout. Ovaries for 

 fecundity samples were removed from all females 

 and were preserved in 10% Formalin solution for 

 at least 48 hr. The eggs were then hand-counted 

 to get total egg counts. The diameters of some 

 eggs from the fecundity samples were measured. 

 These eggs were removed directly from the 

 ovary, water hardened, and placed in Stockard's 

 solution. The diameters were then measured 

 with a vernier measuring microscope calibrated 

 to 0.01 mm. The ages of adult fish were deter- 

 mined by reading scales that had been taken 

 halfway between the lateral line and the poster- 

 ior insertion of the dorsal fin. 



The data for smolts were obtained from fish 

 captured in 1956, 1965, and 1968 in fyke nets 

 fished on the downstream side of the adult 

 counting weir. Fork lengths were taken to the 

 nearest millimeter with a steel millimeter ruler, 

 and weights were taken to the nearest tenth of 

 a gram on a triple-beam balance. As with the 

 adults, the ages of smolts were determined from 

 scales taken halfway between the lateral line and 

 the posterior insertion of the dorsal fin. 



AGE OF COHO SALMON 



The average age composition of coho salmon 

 for several systems in northern and southern 

 latitudes of North America and Asia is shown 

 in Table 1. The differences from the northern 

 to southern latitudes in age composition is sim- 

 ilar to that noted by Marr (1943) and possibly 

 represent a geographic cline. 



The Karluk system had three freshwater age 

 classes," two of which were decidedly predom- 

 inant (Table 1). The three age classes, 43, 54, 

 and 65, designate fish that went to sea in their 

 third, fourth, and fifth years of life and returned 

 to spawn after being at sea for about 1 year. 



"Age classes are designated according to the system 

 developed by Gilbert and Rich (1927). A 43 coho salmon 

 is in its fourth year of life. It went to sea as a smolt 

 at the beginning of its third year, having spent two 

 growing seasons in fresh water. 



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