Kerr et al.: Age validation for Sebastes maliger with bomb radiocarbon 



101 



Table 1 



Range of the year of calculated initial rise in radiocarbon and the associated range of error calculated for bomb radiocarbon 

 regressions. Each regression comprised varying numbers of yelloweye rockfish radiocarbon data points (n = 3, 5, 7, 9, and 11) and 

 was compared to the year of initial 14 C rise and error was determined from all bomb-rise yelloweye rockfish 14 C samples (n=23, 

 last row) to determine the minimum number of quillback rockfish otolith samples sufficient to achieve the desired degree of 

 precision (±2 years). 



Number of data points 

 in regression 



3 

 5 

 7 

 9 

 11 

 23 



Number of 

 regressions 



Range of the year of 

 calculated initial rise in 14 C 



Error range (± years) 



1954.1-1960.3 

 1956.0-1959.4 

 1956.5-1957.9 

 1957.1-1957.3 

 1957.0-1957.8 

 1957.3 



0.8-6.8 

 1.3-2.9 

 1.0-2.5 

 0.9-1.8 

 1.2-1.5 

 n/a 



and Kona (Druffel et al., 2001)— and two otolith-based 

 northern hemisphere 14 C records — for northwest At- 

 lantic haddock (Campana, 1997) and the Barents Sea 

 Arcto-Norwegian cod (Kalish et al., 2001). 



Results 



Sample size assessment 



The estimated years of initial rise in 14 C calculated for 

 the bomb- 14 C regressions, composed of 3, 5, 7, 9, and 

 11 yelloweye rockfish data points spanning 1956 to 

 1971, converged towards the calculated year for all 23 

 data points as the number of samples comprising the 

 regressions increased (Table 1). In parallel, the errors 

 associated with the estimated years of initial rise in 14 C 

 decreased as the number of 14 C samples increased (Table 

 1). The degree of precision within the quillback rock- 

 fish record was limited by the uncertainty associated 

 with age estimates for yelloweye rockfish (a maximum 

 error of ±2 years based on growth zone counts for fish 

 with birth years from 1956 to 1971; Kerr et al., 2004). 

 Examination of the error (years) associated with the 

 year of initial rise in 14 C for the number of data points 

 comprising each regression in relation to our ±2 year 

 criterion indicated that a sample size of nine data points 

 resulted in error values that ranged below 2 years (Table 

 1). Therefore, it was concluded that nine 14 C samples 

 spanning 1956-71 would be sufficient to provide a suit- 

 able degree of precision in the quillback rockfish record. 

 In addition, a limited number of samples, in this case 

 4, were required to establish an average prebomb level 

 for the intercept year. 



Radiocarbon analysis 



The 14 C measured in 15 previously aged quillback rock- 

 fish otoliths with presumed birth years from 1950 to 

 1985 varied considerably over time (Table 2). Otoliths 



from quillback rockfish with birth years 1950-57 con- 

 tained prebomb 14 C levels. Although there was more 

 variation in these prebomb values than expected from 

 14 C uncertainties, the level was relatively consistent over 

 time, averaging -90.7 (±11.5)%c (mean ±SD). A sharp 

 rise in otolith 14 C values was evident in 1959 (±1 year); 



