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Fishery Bulletin 103(1) 



such as age at maturity, rate of growth, longevity, and 

 reproduction frequency (Beamish and McFarlane, 1983). 

 For production (large-scale) aging purposes, age vali- 

 dation is especially important because it provides a 

 standardized basis for ongoing aging efforts to identify 

 strong and weak cohorts (Campana, 2001). 



The most common method of age estimation of bony 

 fishes is counting growth zones in their calcified in- 

 ner ear bones, or otoliths (Chilton and Beamish, 1982; 

 Beamish and McFarlane, 1987). A pair of translucent 

 and opaque growth zones is often assumed to represent 

 one year of growth (Williams and Bedford, 1974). By 

 counting growth zones an estimate of fish age is possi- 

 ble; however, growth patterns are not easily discernible 

 for all species. Age interpretations in long-lived species 

 can be particularly difficult and subjective because 

 of the compression of growth zones within the otolith 

 (Munk, 2001). Therefore, it is necessary to validate the 

 periodicity of growth zones in otoliths with an indepen- 

 dent and objective method. Despite the importance of 

 accurate age estimates for understanding and manag- 

 ing fish populations, validated age and growth charac- 

 teristics are often not available (Beamish and McFar- 

 lane, 1983; Campana, 2001). Traditional age validation 

 techniques, such as captive rearing, mark-recapture, 

 and tag-recapture, can be difficult or impractical for 

 long-lived and deep-dwelling fishes. 



An alternative technique to traditional age valida- 

 tion methods uses radiocarbon ( 14 C) produced by the 

 atmospheric testing of thermonuclear devices in the 

 1950s and 1960s as a time-specific marker (Kalish, 

 1993). This established method of validating otolith- 

 derived age estimates of fishes involves relating the 

 discrete temporal variation of 14 C recorded in otoliths 

 to an established 14 C chronology. Otoliths are closed 

 systems, accreting calcium carbonate throughout the 

 life of the fish and this calcium carbonate is conserved 

 through time. The measurement of bomb-produced 14 C 

 in otoliths of fishes is considered one of the best objec- 

 tive means to validate otolith-based age estimates in 

 long-lived fishes (Campana, 2001). 



This technique is most reliable for fishes that inhabit 

 the surface mixed layer of the ocean, at least during a 

 portion of their life history. Uncertainty regarding mix- 

 ing rate at depth and limited data on the 14 C signal in 

 deeper waters make it difficult to use this technique for 

 organisms that live below the mixed layer throughout 

 their lives (Kalish, 1995, 2001). Studies indicate that 

 the main source of carbon (70-90%) for otoliths is from 

 dissolved inorganic carbon (DIC) in seawater and that 

 the remainder (10-30%) is dietary (Kalish, 1991; Far- 

 rell and Campana, 1996; Schwarcz et al., 1998). An 

 understanding of the life history of the fish (in par- 

 ticular diet, movement, and habitat) and the regional 

 oceanography of the area are integral for interpreting 

 otolith 14 C data. One caveat of this technique is that it 

 must use otoliths with birth dates, including the period 

 of initial increase in 14 C (mid-1950s to mid-1960s; Ka- 

 lish, 1995). Consequently, this technique is well suited 

 for age validation of long-lived species or species for 



which there is an archived otolith collection with birth 

 years that span this period. The application of bomb 14 C 

 for age validation of long-lived species is advantageous, 

 in that it provides a minimum longevity and verifies 

 the periodicity of growth zones in otoliths with only 

 a small amount of material and with a high degree of 

 precision (Kalish, 1993; Campana, 2001). However, the 

 high cost of 14 C analysis (~$400-$500 per sample) has 

 been a limiting factor in the widespread application of 

 this technique. 



The quillback rockfish (Sebastes maliger) is a com- 

 mercially important rockfish that represents a portion 

 (~8%) of the demersal shelf rockfish assemblage land- 

 ings in the Gulf of Alaska (O'Connell et al. 1 ). Species 

 within the demersal shelf group are considered long- 

 lived, late maturing, and sedentary as adults, making 

 them highly susceptible to fishing pressure (O'Connell 

 et al. 1 ). Estimated exploitation rates are low; once ex- 

 ploited beyond a sustainable level, recovery is slow (Lea- 

 man and Beamish, 1984; Francis, 1985; O'Connell et 

 al. 1 ). Longevity estimates for the quillback rockfish are 

 wide ranging, from 15 to 90 years (38 years. Barker, 

 1979; 55 years, Richards and Cass, 1986; 15 years, 

 Reilly et al. 2 ; 76 years, Yamanaka and Kronland, 1997; 

 >32 years, Casillas et al., 1998; 90 years, Munk, 2001), 

 and no age validation has been performed for this spe- 

 cies to date. 



Quillback rockfish are found associated with rocky 

 substrate in relatively shallow continental shelf waters 

 (9 to 146 m) — their abundance decreasing with increas- 

 ing depth below 73 m (Kramer and O'Connell, 1995). As 

 juveniles, quillback rockfish inhabit nearshore benthic 

 habitat. Tagging studies confirmed that they do not 

 demonstrate migratory behavior and are residents in 

 their shallow-water habitat (Matthews, 1990). Because 



1) most longevity estimates indicate that some present- 

 day adult quillback rockfish were born in the prebomb 

 era, 2) quillback rockfish in the juvenile stage are found 

 in the ocean mixed layer, and 3) a suitable 14 C time 

 series exists for the waters off southeast Alaska (previ- 

 ously determined from yelloweye rockfish [S. ruberri- 

 mus] otoliths [Kerr et al., 2004]), the quillback rockfish 

 is an ideal candidate for 14 C age validation. 



The objectives of our study were 1) to develop a meth- 

 od for determining the minimum number of samples 

 required for bomb 14 C age validation to minimize cost, 



2) to validate both age and age estimation methods of 

 the quillback rockfish by measuring 14 C in aged otoliths 

 and to compare the timing of the initial rise in 14 C with 



1 O'Connell, V. M., D. W. Carlile, and C. Brylinsky. 2002. De- 

 mersal shelf rockfish assessment for 2002. Stock assessment 

 and fishery evaluation report for the groundfish resources of 

 the Gulf of Alaska, 36 p. North Pacific Fishery Management 

 Council (NPFMCl, P.O. Box 103136, Anchorage AK 99510. 



2 Reilly, P. N., D. Wilson-Vandenberg, R. N. Lea, C. Wilson, 

 and M. Sullivan. 1994. Recreational angler's guide to 

 the common nearshore fishes of Northern and Central 

 California. California Department of Fish and Game, Marine 

 Resources Leaflet, 57 p. Calif. Dep. Fish and Game, 20 

 Lower Ragsdale Drive, Suite 100, Monterey, CA 93940. 



