FISHERY BULLETIN: VOL. 73, NO. 2 



method to the first three age groups. Because few 

 2- and 3-yr-old hake were present in the samples, 

 Petersen's (1895) method could not be effectively 

 applied. 



According to Graham's (1929) second method, 

 observations of the development of translucent 

 and opaque zones on the perimeter of the otolith 

 (based on data from a population that had been 

 sampled periodically during a year) may provide 

 an indication of the frequency with which the 

 zones are formed. A single occurrence of a par- 

 ticular zone during a year would provide an annual 

 mark which may be suitable for age determina- 

 tion. In European hake (Hickling 1933) opaque 

 zones have been associated with good physical 

 condition and growth whereas translucent zones 

 have been associated with a lesser physical well- 

 being and retardation or cessation of growth. Poor 

 condition can result from a decrease in the food 

 supply, the onset of maturation and spawning, or 

 both. 



For the present study a special effort was made 

 to record the zone type on the edge of all hake 

 otoliths collected during 1967. Samples were taken 

 during March, April, May, June, and August. 

 Otoliths from a sample collected in November 1969 

 were added to the above spring and summer 

 samples for data on the winter appearance of the 

 edge. It appears that there are long and overlap- 

 ping periods when zones are deposited because 

 most samples had some otoliths with opaque mar- 

 gins and others with translucent margins. One 

 exception is the small, March 1967 sample that 

 contains only 1-yr-olds. Even though opaque edges 

 are plainly recognizable in the young age groups, 

 all otoliths in this sample had translucent mar- 

 gins. 



The persistent occurrence during the summer 

 (the apparent growing season) of otoliths with a 

 translucent edge may be at least partly because 

 the newly deposited opaque material is not always 

 detectable due to the thinness of the edge and the 

 resulting transparency. 



Figure 2 demonstrates that the frequency of 

 opaque edges decreases rapidly with the age of the 

 fish. This is almost certainly a bias resulting from 

 the increased difficulty in distinguishing the zone 

 type on the edge of the otolith as the fish becomes 

 older. Opaque bands on the otoliths of young fish 

 (1-4 yr) growing at a relatively fast rate are wide, 

 dense, and readily distinguishable. As growth 

 slows in older specimens, new opaque zones 

 become narrower, and are not always apparent 



100 

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 40 

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 80 

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MARCH 1967 



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 MAY 1967 



APRIL 1967 



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AUGUST 1967 



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AGE ( years ) 



Figure 2.-Percentage of otoliths with opaque edges by age 

 group (ages actually observed in bold print). 



until late in the growing season or until bordered 

 by a new translucent zone. 



Because the zone type on the edge of the otolith 

 is related to the age of the fish, a comparison of 

 otoliths could be misleading if the sample age 

 compositions vary to a large extent. Whereas the 

 age compositions of the 1967 samples were similar, 

 the age composition of the 1969 sample was no- 

 ticeably different (Figure 3). To avoid the effects 

 of advanced fish age on a reader's ability to ac- 

 curately judge opaque zones at the otolith edge 

 type, samples of 6-yr-olds taken in April- 

 November and one sample of 1-yr-olds taken in 

 March were compared in Figure 4. The graph 

 suggests that Pacific hake start to deposit opaque 

 material around April. The time of deposition may 

 vary with age, but other age groups were not 

 present in numbers adequate for comparison. The 

 incidence of otoliths with opaque edges increased 

 steadily through August when it peaked at about 

 72%. A dramatic decrease in otoliths with opaque 

 edges occurred in the November sample. The 

 foregoing analysis indicates that the physical 

 well-being of Pacific hake improves in early spring 



340 



