BOEHLERT: AGE DETERMINATION IN FISHES 



otoliths) show a clear mode at 7 yr for both males 

 and females, with whole otolith age ranges from 1 

 to 46 for males and to 55 for females. Mean 

 lengths-at-age for males and females are similar 

 until age 8, after which females grow more rapidly 

 (Boehlert 1980; Boehlert and Kappenman 1980). 



Subsampling every fourth pair of otoliths from 

 all collections of S. diploproa resulted in 290 



female and 246 male specimens. The subsample 

 was representative of the latitudinal distribution, 

 age range, and length range of the whole collec- 

 tion. Capture, otolith, and age data from these 

 samples are summarized in Table 1. Otolith sec- 

 tion ages, as expected, were typically greater than 

 whole otolith ages (Table 1); this was particularly 

 true at greater lengths. Correlation matrices of 

 pertinent otolith and age data (Table 2) show that 

 otolith weight has the strongest linear association 

 with otolith section age; both otolith weight and 

 age are exponential functions offish length. Plot- 

 ting otolith length, fish length, and otolith weight 

 against otolith section age demonstrates the pat- 

 tern of otolith growth (Fig. 3). Past an age of about 

 25 yr, both otolith length and fork length reach 

 approximate asymptotes, whereas otolith weight 

 continues to increase. The wide fluctuations in 

 otolith weight apparent at older ages correlate 

 closely with changes in fork length (Fig. 3 ); for this 

 reason, otolith weight alone is a relatively poor 

 predictor of fish age at greater ages where fork 

 length is highly variable. Addition of otolith 



FIGURE 2. — Locations of 1980 West Coast Survey collections 

 from which otoliths of Sebastes diploproa were taken. 



10 20 30 40 50 60 70 



OTOLITH SECTION AGE (YEARS) 



Figure 3. — Otolith characteristics of male Sebastes diploproa 

 from the calibration subsample as related to fish length and 

 age. A'' = 246. Note the covariation among the three curves, 

 particularly at older ages. 



Table l. — Summary of biological and otolith data from the subsampled groups of Sebastes diploproa 



used in developing the age models. 



Females (N = 290) 



Males (W = 246) 



Variable 



Minimum Maximum Mean 



SD 



Minimum Maximum 



Mean 



SD 



Depth of capture (fathoms) 34 185 137 29.36 53 185 136 28.45 



Fork length (mm) 130 378 264 56.16 94 364 246 48.19 



Otolith length (mm) 7.71 18.02 12.49 2.35 5.47 17.03 11.82 2.14 



Otolith width (mm) 5.08 11.25 7.97 1.31 3.59 10.32 7.57 1.14 



Otolith thickness (mm) 0.83 2.97 1.41 0.44 0.73 2.84 1.35 0.39 



Otolith dry weight (mg) 59 724 244.6 150.4 25 659 208 117.4 



Whole otolith age (yr) 1 56 15.2 11.97 1 40 13.5 9.78 



Otolith section age (yr) 2 66 17.2 15.68 1 74 16.9 16.41 



107 



