FISHERY BULLETIN: VOL. 73, NO. 2 



Figure 18.-Average body weight at various ages for Pacific hake 

 collected off California, Oregon, and Washington, 1965-69. 



more than males. For each sex, Table 10 gives 

 average weight at age values, annual grovv^th 

 rates, and annual instantaneous growth rates, as- 

 suming exponential growth in weight. 



SUMMARY AND CONCLUSIONS 



Biological data from samples of Pacific hake 

 taken in 1964-69 off the coasts of Washington, 

 Oregon, and California were utilized to study the 

 age and growth of the species. 



Table lO.-Mean weight, annual increase in weight, and instan- 

 taneous growth rate at various ages for male and female hake 

 taken off California, Oregon, and Washington, 1964-69. 



The method of age determination from annuli 

 on otoliths was e)tamined, and all evidence sug- 

 gests that the method provided reliable age 

 data. 



Several sources of variation in the age structure 

 of the population were considered. The relative 

 size of newly recruited year classes varied sub- 

 stantially, creating noticeably annual variation in 

 the age composition. There was no detectable 

 seasonal variation in the age composition of the 

 hake population found off Washington from 

 spring through fall. Latitudinal stratification of 

 hake by age (known to occur over large 

 geographical areas) was further examined, and 

 some variation in age composition was found even 

 among 1/2 degree intervals of latitude off the 

 Washington coast. The relative abundance of the 

 4- and 5-yr-olds decreased as sampling progressed 

 northward from the mouth of the Columbia River 

 to the Strait of Juan de Fuca, while the relative 

 abundance of 7- to 10-yr-olds increased. This strat- 

 ification of ages by latitude supports the theory 

 that there is a northward migration of hake in the 

 early spring along the Pacific coast of North 

 America with the older (larger) individuals tend- 

 ing to migrate farthest. There is little variation in 

 age composition due to sex, except that the longer 

 lived females tend to predominate from 8 to 10 yr 

 of age and are usually the sole survivors at 11-13 yr 

 of age. 



Pacific hake grow rapidly in length during their 

 first 3 yr after which growth slows and becomes 

 asymptotic. At about 4 yr of age, females grow 

 noticeably faster and by age 11 may average 3.12 

 cm longer than males. Individual males may reach 

 66 cm, while some females may reach 80 cm in 

 length. Year class variation in growth rates was 

 detected by analysis of age-length data and back 

 calculation of growth from otoliths. The equation 

 Y = 18.78957 - 3.79065A' + 0.67490A^ - 0.01836A' 

 was used to describe the relationship of body 

 length (7) and otolith radius (X). 



The extraordinarily large 1961 year class grew 

 at a substantially slower rate than the 1957-60 

 year classes. This difference possibly is indicative 

 of density-dependent growth. Growth in length 

 can be expressed adequately by the von Ber- 

 talanffy growth equations: 



If = 56.29 ( 1-^ -0.39 (/ -0.20)) for males, 



I, = 61.23 (l-(-'''^«"-ooi') for females, and 



/, - 60.85 (l-e -0-30 ((-0.03)) f^^ ^^^ gg^es combined. 



354 



