tion by the European method is sho\\'n in paren- 

 theses. 



In the Gilbert and Rich designations, an Ara- 

 bic numeral indicates the number of winters 

 from spawning of the parents to capture. A 

 second digit, usually written as a subscript, in- 

 dicates the winters from spawning of the par- 

 ents to seaward migration. Because the fish do 

 not form scales until after the first winter in the 

 gravel, tlie number of winters of gro\vth is one 

 less than shown by the age formula, but the fish 

 is in the indicated year of life. To assign a fish 

 to its parent brood year, subtract the first digit 

 from the year of capture; e.g., a fish of age 

 group 5;; caught in 1965 was produced by the 

 spawning in 1960 and migrated to the ocean in 

 1963. Scientists of the U.S.S.R. use a modified 

 Gilbert and Rich system in which the age is com- 

 puted from hatching instead of spawning of the 

 parents (Krogius, 1958; Chugunova, 1959). 



In the European method, the number of win- 

 ters the fish spent in fresh water from hatching 

 and in the ocean are separated by a dot. To deter- 

 mine the year of spawning that produced tlie 

 fish, add 1 to the sum of the two digits and suId- 

 tract from the year of capture. 



A comparison of the major age groups in the 

 three metliods of age designation follows : 



Runs of sockeye salmon often include individ- 

 uals, considerably smaller than the average, that 

 liave returned to spawn after only one winter at 

 sea. These fish are kno\\Ti as "jacks" as they are 

 almost invariably males, except in the Coliunbia 

 River where they may be of either sex." 



In tlie following plates the winter growth 

 zones are indicated by arrows — wide arrows in 

 the ocean portion of the scale (plates 12-18) and 

 narrow arrows in the fresh-water portion 



11 Occasionally the small females in the Columbia River are called 

 "jennies." 



(plates 13-18). Stub arrows when present indi- 

 cate the end of plus gi'owth. 



AGE GROUPS WITH NO SCALE GROWTH IN 

 FRESH WATER (Plate 12) 



Fish of these age groups migrate to the sea 

 before or immediately after scale formation. 

 Because most sockeye salmon live in fresh water 

 for a year or more, few scales of these ages are 

 collected; they are usually in the 3^ and 4^ age 

 groups. 



Examples of these age groups are showTi: 



Age group 2^. (0.1) one winter in the ocean 

 zone. Spawning fish are "jacks." 



Age group 3i. (0.2) two winters in the ocean 



zone. 

 Age group 4i. (0.3) three winters in the ocean 



zone. 

 Age group S^. (0.4) four winters in the ocean 



zone. 



AGE GROUPS WITH ONE GROWING SEASON IN 

 FRESH WATER (Plate 13) 



These age gi'oups make up many of the impor- 

 tant runs of sockeye salmon. From tlie Columbia 

 to the Copper River, and in the Wood River- 

 Nushagak system in Bristol Bay, fish with this 

 fresh-watei' histoiy predominate every year. 



Fish of a given year class may first be present 

 in a spawTiing run as age group 3o ("jacks") ; 

 dominate the run the next year as age group 

 4o and (in some areas) the following year as age 

 group 5-2 ; and provide occasional 6o's and T^'s in 

 subsequent years. Tlius, it is possible that fish of 

 a year class with one growing season in fresh 

 water could be present in the spawning migration 

 over a 5-year period, but in most areas the period 

 lasts only 3 or 4 years. 



Examples of the following age groups are 

 shown : 



Age group 2o (1.0). One winter in fresh water, 



none in the ocean. (This illustration is from an 



immature fish, not an adult.) 

 Age group 3^ (1.1). One winter in fresh water, 



one in the ocean. 

 Age group 4o (1.2). One winter in fresh water, 



two in the ocean. 



262 



U.S. FISH AND WILDLIFE SERVICE 



