DARK: AGE AND GROWTH OF PACIFIC HAKE 



80r 



1967 Samples 



\ 1969 Sample 



AGE (year) 



Figure 3.-Age composition of samples selected for analysis of zone type on the otolith 



edge. 



100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



(1561 



MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 



Figure 4.-Percentage of otoliths with opaque edges by month of 

 collection, 1967-69. (Sample size occurs in parentheses.) 



(indicated by the appearance of the opaque zone in 

 the otolith edge). Growth occurs throughout the 

 summer until sometime after August. The onset of 

 maturation and the spawning migration in late 

 fall probably place additional demands on the 

 energies of the animal, resulting in slowed growth 

 which is reflected in the appearance of the 

 translucent zone at the otolith edge. 



Although observations are not available during 

 all months, the unimodal characteristic of the 

 curve in Figure 4 strongly suggests that one 

 opaque and one translucent zone are deposited 

 each year and that the zones provide reliable an- 

 nual marks. However, comprehensive monthly 

 sampling is required to confirm unimodality. 



The third method suggested by Graham (1929) is 

 based on the rationale that if a predominant year 



class enters a population of fish and if the aging 

 technique is reasonably reliable, then the year 

 class should be observed progressing normally 

 through the population age structure for several 

 years. 



Fortunately the 1961 year class of Pacific hake 

 was extremely strong when it was partially 

 recruited (designated as 4-yr-olds) to the adult 

 hake population in 1965. In that year the 4-yr-olds 

 comprised 15% of the adult population off 

 Washington, while in other years from 1964 to 

 1969, 4-yr-olds contributed only 0-2%. In 1966 

 sampling indicated that over 50% of the adult 

 population off Washington was composed of 5-yr- 

 old hake. The dominance of the 1961 year class 

 evidently continued through 1967, when over 70% 

 of the population was 6-yr-olds; 1968 when about 

 64% was 7-yr-olds; and 1969 when about 24% was 

 8-yr-olds (Figure 5). In contrast, from 1964 to 1968, 

 8-yr-olds comprised only 2.4-13.7% of the popula- 

 tion. This movement of the 1961 year class through 

 the population age structure is accepted as addi- 

 tional evidence that the translucent zone 

 represents a single annual mark. 



Randomization of Age Samples 



As noted previously some otolith samples used 

 herein were collected aboard research vessels and 

 are considered to be random, but the majority 

 were commercial samples in which otoliths were 



341 



