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



105 



ties of the AMS 14 C measurements (~±3-4%o). Elevated 

 14 C levels have also been recorded in otoliths of the 

 black drum {Pogonias cromis), known to reside in es- 

 tuaries during the juvenile stage (Campana and Jones, 

 1998); these elevated values are attributed to the rapid 

 exchange of atmospheric 14 C in the well-mixed estuarine 

 environment and the influence of river input. Quillback 

 rockfish are known to inhabit more nearshore waters 

 than those inhabited by yelloweye rockfish (Love et al., 

 2002), which could explain the elevated 14 C levels. 



The core-extraction method was designed to limit the 

 inclusion of more recently formed material (older than 

 age 1); however, the inclusion of some of this material 

 may have inadvertently occurred, perhaps introducing 

 error to the quillback rockfish 14 C record. This kind 

 of error could alter the 14 C value from the actual core 

 year value depending on the time of otolith formation 

 in relation to the bomb 14 C signal. A small addition of 

 material with 14 C content different from the core ma- 

 terial, however, may not produce a significant change 

 in the timing of the initial rise and the shape of the 

 rise. We feel that in most cases this would lead to an 

 underaging of the fish and provide us with a minimum 

 age estimate. 



Perhaps the most significant potential source of er- 

 ror is the uncertainty associated with age estimation 

 methods (coefficient of variation=2.6%). Growth zone 

 counting error could have contributed to variation in 

 the quillback rockfish record; however, the otoliths used 

 in our study were chosen specifically to provide clearly 

 definable growth zones and the highest rank in age-es- 

 timate confidence. The samples chosen were best-case 

 examples of precise age determinations. 



Short-term regional-scale changes in oceanographic 

 conditions, such as upwelling events, may have affected 

 14 C levels at the time of otolith formation. The variation 

 in postbomb measurements exemplifies this factor. 



Considering the discussions above and the similar 

 biology, ecology, and distribution of the two rockfish 

 species, we believe that the use of the yelloweye rockfish 

 14 C time-series (Kerr et al., 2004) as a means of tempo- 

 ral calibration for the quillback rockfish record is well 

 supported. The year of initial rise in 14 C for quillback 

 rockfish otoliths (1959 [±1 year]) is in agreement with 

 the yelloweye rockfish record (1958 [±2 years]); this 

 finding validates the age estimates of the quillback 

 rockfish and the accuracy of the break-and-burn age 

 estimation method. In addition, the concordance of the 

 quillback time series (1950 to 1985) provides further 

 support for the age validation. Note that the 14 C levels, 

 timing of the peak, and the subsequent decline were 

 similar between species. In addition, all but two of 

 the quillback rockfish 14 C values (sample years 1967 

 and 1980) fell within the confidence intervals for the 

 yelloweye rockfish 14 C curve, further supporting the 

 concordance of the two rockfish records. If there had 

 been consistent underaging or overaging of quillback 

 rockfish otoliths, this discrepancy would have resulted 

 in a chronology that was not in phase with the yellow- 

 eye rockfish time series (Campana et al., 2002). 



This application of the bomb- 14 C technique has con- 

 firmed the longevity of quillback rockfish to a minimum 

 of 43 (±1) years. This minimum age estimate is based on 

 the last individual fish sample (estimated birth year of 

 1957 from growth zone counting) to have prebomb levels, 

 immediately preceding the significant rise in 14 C levels 

 observed in 1959 (±1) year. These findings effectively 

 refute previous longevity estimates less than 43 years 

 (Barker, 1979; Reilly et al. 2 ). In addition, it is reasonable 

 to assume that the annual growth pattern continues 

 throughout life; hence, these findings strongly support 

 longevity estimates exceeding 43 years and ranging up 

 to 90 years (Richards and Cass, 1986; Yamanaka and 

 Kronland, 1997; Casillas et al., 1998; Munk, 2001). 



Conclusions 



It is our intention to not only validate the age and age 

 estimation method for the quillback rockfish, but to 

 determine the most effective number of samples for age 

 validation with bomb radiocarbon. From our results, it 

 appears that the concordance of the full 14 C time series 

 is not entirely necessary for validating the age of fish, 

 and perhaps of any other organism. Because the evolu- 

 tion and magnitude of the bomb- 14 C rise from the pre- 

 bomb to postbomb era is subject to variations due to the 

 specific oceanography of the region, the 14 C time series 

 are in fact regional and are not universally applicable 

 to all validation studies. The agreement of the entire 

 14 C time series does not provide additional information 

 relevant to age validation. Hence, we propose that the 

 year-of-initial-rise method be considered an effective 

 14 C age validation approach. This method both reduces 

 the number of samples required for age validation and 

 effectively precludes the perceived need to establish a 

 pre- to postbomb 14 C reference time series for every 

 region of the world's oceans. Because the year of initial 

 rise in 14 C levels in surface waters is well defined (1958 

 [±2 years]), it should be treated as a time-specific marker 

 for organisms that inhabit the mixed layer of the oceans 

 for some or all of their life cycle. 



Acknowledgments 



We thank the Alaska Department of Fish and Game 

 for providing aged otolith samples. This article was 

 supported in part by the National Sea Grant College 

 Program of the U.S. Department of Commerce's National 

 Oceanic and Atmospheric Administration under NOAA 

 Grant no. NA06RG0142, project number R/F-190, 

 through the California Sea Grant College Program, 

 and in part by the California State Resources Agency. 

 This work was performed, in part, under the auspices 

 of the U.S. Department of Energy by University of Cali- 

 fornia, Lawrence Livermore National Laboratory under 

 contract no. W-7405-Eng-48. This research was also 

 funded in part by the Pacific States Marine Fisheries 

 Commission, Earl H. and Ethel M. Myers Oceanographic 



