127 



Abstract— This study was undertaken 

 to resolve problems in age determina- 

 tion of sablefish (Anoplopoma fimbria). 

 Aging of this species has been ham- 

 pered by poor agreement (averaging 

 less than 45%) among age readers and 

 by differences in assigned ages of as 

 much as 15 years. 



Otoliths from fish that had been 

 injected with oxytetracycline (OTC) 

 and that had been at liberty for known 

 durations were used to determine why 

 age determinations were so difficult 

 and to help determine the correct aging 

 procedure. All fish were sampled from 

 Oregon southwards, which represents 

 the southern part of their range. The 

 otoliths were examined with the aid of 

 image processing. 



Some fish showed little or no growth 

 on the otolith after eight months at 

 liberty, whereas otoliths from other fish 

 grew substantially. Some fish lay down 

 two prominent hyaline zones within a 

 single year, one in the summer and one 

 in the winter. We classified the otoliths 

 by morphological type and found that 

 certain types are more likely to lay 

 down multiple hyaline zones and other 

 types are likely to lay down little or no 

 zones. This finding suggests that some 

 improvement could be achieved by 

 detailed knowledge of the growth char- 

 acteristics of the different types. 



This study suggests that it may not 

 be possible to obtain reliable ages from 

 sablefish otoliths. At the very least, 

 more studies will be required to under- 

 stand the growth of sablefish otoliths. 



Sources of age determination errors for sablefish 

 (Anoplopoma fimbria)* 



Donald E. Pearson 



Santa Cruz Laboratory 



National Marine Fisheries Service 



1 10 Shaffer Road 



Santa Cruz, California 95060 



E-mail address Don Pearsom&Noaa Gov 



Franklin R. Shaw 



Alaska Fisheries Science Center 

 National Marine Fisheries Service 

 7600 Sand Point Way NE 

 Seattle, Washington 98118 



Manuscript approved for publication 

 14 July 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish Bull. 102:127-141 (2004). 



Sablefish (Anoplopoma fimbria) are a 

 valuable groundfish resource off the 

 west coast of North America. The fish- 

 ery in California, Oregon, and Wash- 

 ington is tightly regulated according 

 to periodic stock assessments. Between 

 1990 and 1998 landings averaged more 

 than 8000 metric tons per year and an 

 average exvessel (retail) value of 12.5 

 million dollars per year (PFMC, 1999). 



Sablefish are distributed in the 

 northeastern Pacific Ocean from 

 Baja California to the Bering Sea and 

 southeast to northern Japan (Miller 

 and Lea, 1972). Males and females are 

 sexually mature between 55 and 67 cm, 

 although there is considerable variation 

 (Fujiwara and Hankin 1988a; Hunter et 

 al, 1989). Off Washington, Oregon, and 

 California, sablefish spawn from Octo- 

 ber through April and spawning peaks 

 in January and February. Sablefish are 

 oviparous, releasing eggs that float 

 near the surface (Hunter et al., 1989). 

 After hatching, larvae and juveniles in- 

 habit surface waters offshore for several 

 years after which they migrate inshore 

 and settle to the bottom. 



Sablefish are found on the continen- 

 tal slope and are commercially fished at 

 depths from 200 to 1400 meters (Leet et 

 al., 1992). Adult sablefish feed on fish, 

 cephalopods, and crustaceans (Laidig 

 et al., 1998). They reach a maximum 

 length of 102 cm (Miller and Lea, 1972) 

 and are believed to be a very long-lived 

 species (possibly 100 years or more). 



Many physical features have been 

 used to age this species, including 



scales, finrays, thin-sectioned otoliths, 

 and broken and burned otoliths, but all 

 methods have resulted in less than 45% 

 agreement among readers (Lai, 1985; 

 Fujiwara and Hankin 1988b; Kimura 

 and Lyons, 1991; Heifetz et al. 1999). 

 The broken and burned otolith method 

 (Chilton and Beamish. 1982) is the 

 principal method used in aging of the 

 species in both the United States and 

 Canada. Typically, age readers agree 

 on ages less than 50% of the time, and 

 for fish older than 7 years, agreement 

 drops to less than 15% (Kimura and 

 Lyons. 1991). 



There have been repeated efforts at 

 validating sablefish ages and develop- 

 ing aging criteria. Beamish et al. ( 1983) 

 successfully used oxytetracycline (OTC ) 

 marking to validate ages and repeated 

 his experiment in 1995 when additional 

 marked fish were recovered (MacFar- 

 lane and Beamish, 1995). Lai (1985) 

 validated the use of otoliths for aging 

 sablefish. Fujiwara and Hankin ( 1988b) 

 examined otolith growth characteristics 

 to help refine aging criteria. Heifetz et 

 al. (1999) validated the currently ac- 

 cepted aging practices and examined 

 sources of error in the aging of sablefish. 

 Kastelle et al. (1994) used radiometric 

 methods to generally validate the aging 

 criteria currently used. Even with all of 

 these studies that have validated age 



* Contribution 119 from the Santa Cruz La- 

 boratory, National Marine Fisheries Ser- 

 vice, Santa Cruz, CA 95060. 



