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Fishery Bulletin 93(2), 1995 



cores ranged from 0.0179 to 0.0290 dpm-g : and 

 showed a mean value of 0.0223 ±0.0036 dpm-g" 1 . The 

 226 Ra values found for the cores were consistent with 

 our earlier analysis (Fenton et al., 1990) of whole 

 otoliths (see Discussion section) and further confirmed 

 that the core represents approximately a 2+ fish. 



In order to select the value of R, the initial activity 

 ratio used in the calculation of age, we examined our 

 previous data for whole otoliths (Fenton et al., 1990) 

 and the stable element analysis of Pb and Ba (dis- 

 cussed above). From the data for a 1+ fish a value of 

 R<0.06 is indicated; however, data for 0+ fish indi- 

 cate R could be as high as 0.1. A value of #=0.05 ap- 

 pears to be the best estimate for the initial activity. 

 If R were as high as 0.1, it would lower the age esti- 

 mate by approximately 9 months. Conversely, if R 

 =0, ages would be higher by 2.6 years. The differ- 

 ence that a lower or higher value makes to the age 

 estimates is well within the error associated with 

 each radiometric age calculated by using R=0.05. 



Otolith core ages were calculated by using both the 

 individual sample 226 Ra value and the mean 226 Ra 

 value. This has little effect on the average age of all 

 the cores analyzed (e.g. 10.2 ±5.0 years [with indi- 

 vidual 226 Ra] and 9.6 ±3.2 years [with mean 226 Ra]), 

 but the maximum age recorded changes from 17.9 

 (+10.2, -7.7) years (with individual 226 Ra) to 13.3 



(+7.1, -5.8) years (with mean 226 Ra) depending on 

 which radium value is used. Since all individual 226 Ra 

 activity ratios are similar within experimental er- 

 ror, it follows that the best age estimates are calcu- 

 lated by using the mean 226 Ra activity. 



Age estimates from annulus counts conducted by 

 Kenchington and Augustine (1987) relative to fish 

 length and otolith weight are plotted together with 

 the radiometric core age estimates in Figure 1. The 

 radiometric analysis of otolith cores are similar to 

 those assigned by Kenchington and Augustine ( 1987 ), 

 although there is some indication that the radiomet- 

 ric ages may be slightly lower. However, the core 

 samples represent the average age of only three fish, 

 the errors associated with the radiometric analyses 

 are large, and limited sample sizes preclude any 

 meaningful statistical analysis. 



Discussion 



Radiometric analysis of otolith cores has successfully 

 provided age estimates for blue grenadier, in contrast 

 to the unsuccessful analysis of whole otoliths by 

 Fenton et al. (1990). The average age of the otolith 

 core samples was approximately 10 years for fish 95- 

 110 cm in length. 



