Abstract. Age determination 



of sablefish (Anoplopoma fimbria) 

 is typically done by counting 

 growth zones on the burnt cross- 

 section of the otolith. The break- 

 and-burn method of age determi- 

 nation is difficult to apply to sable- 

 fish. Therefore, we applied a rela- 

 tively new method of fish age vali- 

 dation, using the disequilibrium of 

 Pb-210/Ra-226 in the otoliths. This 

 method of validation complements 

 previous methods which used 

 oxytetracycline (OTC) marking to 

 validate incremental growth in 

 sablefish otoliths. The Pb-210/Ra- 

 226 disequilibria generally con- 

 firmed the ageing criteria used to 

 interpret the otolith's burnt cross- 

 section. 



Using Pb-210/Ra-226 disequilibria 

 for sablefish, Anoplopoma fimbria, 

 age validation 



Craig R. Kastelle 

 Daniel K. Kimura 



Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA 

 7600 Sand Point Way NE, Seattle, WA 981 15-0070 



Ahmad E. Nevissi 

 Donald R. Gunderson 



School of Fisheries, WH-10, University of Washington 

 Seattle, WA 98195 



Manuscript accepted 27 October 1993 

 Fishery Bulletin 92:292-301 (1994) 



Sablefish (Anoplopoma fimbria) is 

 an important commercial species 

 distributed continuously along the 

 North Pacific Rim from California 

 to northern Japan. On central 

 California's continental shelf, the 

 spawning of sablefish takes place 

 from October to February at depths 

 of over 823 m (Hunter et al., 1989). 

 Both eggs and larvae have been 

 collected at depths of over 400 m in 

 April off British Columbia. After 

 hatching, postlarval sablefish move 

 into the surface waters where on- 

 shore or offshore transport may 

 take place (Mason et al., 1983). 

 Postlarvae have been found off- 

 shore, but as juveniles they are 

 usually seen inshore (Bracken, 

 1983; Mason et al., 1983). The ju- 

 veniles are believed to reside in- 

 shore for several years and then 

 move to deeper offshore waters as 

 they near maturity and join the 

 spawning population (Bracken, 

 1983; Mason et al., 1983). Mature 

 sablefish are typically caught at 

 700 m (Mason et al., 1983). Funk 

 and Bracken 1 note that the growth 

 of young fish is fast compared to 

 very slow growth of mature fish. An 

 abrupt slowing of growth coincides 

 with the onset of sexual maturity. 

 Mean fork length increases with 

 depth and the length at 50% matu- 



rity for females is 60 cm (Hunter et 

 al., 1989). 



At the Alaska Fisheries Science 

 Center (AFSC) sablefish ages are 

 determined by counting growth 

 zones (assumed annular) seen on 

 the distal surface of the otolith, or 

 more frequently in the burnt dor- 

 sal-ventral cross-section (break- 

 and-burn method, Beamish et al., 

 1983). Even though ageing criteria 

 have been established for sablefish 

 by using the break-and-burn 

 method (Beamish and Chilton, 

 1982; Beamish et al., 1983), vari- 

 ability between individual sablefish 

 in the morphology of their otoliths 

 and the appearance of growth 

 zones makes this method difficult 

 to apply. Between-reader variabil- 

 ity in sablefish ages are far greater 

 than for any other species routinely 

 aged at the AFSC (Kimura and 

 Lyons, 1991). 



Sablefish age validation has been 

 examined by using oxytetracycline 

 (OTC) studies, mark and recapture 

 of known age fish, tagging studies, 

 length-frequency analysis of young 

 fish, and daily growth zone counts in 

 juvenile sablefish otoliths (Beamish 



'Funk, F., and B. E. Bracken. 1983. 

 Growth of sablefish in southeastern 

 Alaska. AK Dept. Fish and Game Info. 

 Leaflet No. 223, 40 p. 



292 



