FISHERY BULLETIN: VOL. 70. NO. 1 



USSR, is similar to that of coho salmon in the 

 northern areas of the west coast of North Amer- 

 ica. The main age classes are 82 and 43 (Table 

 1 ) . The ratio of one age class to the other varies, 

 however, from year to year and from area to 

 area (Gribanov, 1948; Semko, 1954). 



An additional comparison of the age compo- 

 sition of coho salmon from northern to southern 

 latitudes is shown in Figure 2, which gives the 

 percent age composition of the major age classes 

 from five geographical areas along the west coast 

 of North America. In California, the southern 

 limit of the range of coho salmon, the major age 

 class is 82, but jack salmon (age 22) contribute 

 significantly to the runs. The 82 age class is still 

 dominant in Washington, but the number of jack 

 salmon is less and 43 fish are starting to appear. 

 North of Washington to central British Colum- 

 bia, more than 95 ^r of the fish are age 82, and 

 there are only traces of other age classes, mainly 

 the 43 class. From central British Columbia and 

 northward through Alaska, the primary age 

 class is 43; 82 fish are the secondary class and 54 

 fish are found in small numbers. In Alaska, the 

 increase in total age is the result of juvenile coho 

 salmon residing an additional year in fresh water 

 before migrating to sea. Possible exceptions to 

 the dominance of the 43 age class in Alaska are 

 the Ketchikan River, Dairy Creek, Yukon River, 

 and Karluk River systems (Table 1). In the 

 first three river systems, 82 fish are the dominant 

 age class and 43 fish the secondary class. The 

 sizes of the samples from these systems were 

 small, however (less than 25 fish). In the Kar- 

 luk system, although 43 fish were dominant, 64 

 fish rather than 82 fish were the secondary age 

 class (Figure 2). 



100 



"50 



CALIFORNIA 



WASHINGTON 



"n 11^ I ^11 



BRITISH 

 COLUMBIA 



ALASKA 



KARLUK 

 RIVER 



i 



h h \ \ S h S h S ^ S ^ 



AGE CLASS 



Figure 2. — Average age composition of coho salmon runs 

 along the west coast of North America by geographical 

 area (minor age classes omitted). 



The presence of older fish (bi) in northern 

 latitudes may be a result of the juveniles being 

 reared in lakes rather than rivers. Typically, 

 coho salmon spawn in rivers or tributaries to 

 rivers and the emerging fry reside in these areas 

 until they migrate to sea. In contrast, in some 

 Alaska river systems where 54 fish are part of 

 the run (Table 1 and Figure 2), the juveniles 

 migrate from spawning grounds to lakes before 

 migrating to sea. It appears that some of the 

 juveniles that reside in lakes (lake type) go to 

 sea at an older age than those that reside in rivers 

 (river type)/ 



NUMBER AND SIZE OF EGGS 



In this section, information is presented on 

 fecundity (number of eggs contained in a fe- 

 male) as a function of latitude and length, the 

 relative numbers of eggs in right and left ovaries, 

 and egg size in relation to length and fecundity. 

 Fecundity and factors related to it form the basis 

 for determining the reproductive potential of a 

 spawning stock and subsequent survival from 

 egg to young. Knowledge of variations in fe- 

 cundity and egg size is of increasing importance 

 in fish stocking and fish rehabilitation programs. 

 Size of egg may be useful in predicting the con- 

 dition, or hardiness, of developing fry. Because 

 the fecundity of fish differs among geographic 

 areas, the reproductive potential must be deter- 

 mined for each stock. 



FECUNDITY AS A FUNCTION 

 OF LATITUDE 



The average fecundity for both North Amer- 

 ican and Asiatic stocks of coho salmon is con- 

 siderably higher in fish from northern latitudes 

 than in those from southern latitudes (Table 2 

 and Figure 8) , Coho salmon from Alaska river 

 systems (with the exception of the two small 

 samples from Port Herbert and Sashin Creek) 



* Personal communication, 1969, Charles J. DiCos- 

 tanzo, Chief, Salmon Investigations, National Marine 

 Fisheries Service, Auke Bay Fisheries Laboratory, Auke 

 Bay, Alaska 99821. 



82 



