FISHERY BULLETIN: VOL. 83, NO. 2 



systems based upon differential light transmis- 

 sion (Fawell 1974; Mason 1974). These techniques 

 have generally not been implemented, however, 

 due to the subjective and variable nature of the 

 criteria. Implementation of these techniques with 

 automated systems could result in even further 

 savings of time. 



Since estimating the age distribution of 

 exploited fish populations remains an important 

 part of fishery biology, new and improved 

 techniques of age determination are desirable. For 

 shorter lived species, length-based methods are 

 proving important (Pauly and David 1981). Age- 

 length keys are also used quite extensively. Sam- 

 ple sizes necessary for accurate age-length keys, 

 however, must be quite large, particularly for 

 long-lived species such as Sebastes. In my rela- 

 tively small calibration subsamples, for example, 

 there are up to 15 age classes in a single 1 cm 

 length interval (Table 15). Considering the 



Table 15. — Number of age classes within single 1 cm length 

 intervals from the calibration subsample. A'^ = number of 

 Sebastes specimens in the subsample. 



maximum age of S. diploproa (Bennett et al. 1982), 

 there could potentially be up to 50 age classes in a 

 single length interval if a sufficient sample size 

 were taken. For such species, age-length keys will 

 be difficult to extrapolate meaningfully to the en- 

 tire population without very large sample sizes, 

 which must accordingly be aged. Similar, but more 

 severe, problems will apply to techniques which 

 attempt to extract growth parameters from 

 length-frequency data for such long-lived species. 

 The techniques developed by Pauly and David 

 (1981) for faster growing species would be com- 

 plemented by the current technique for slow- 

 growing, difficult-to-age species. Otoliths could be 

 collected by station, sex, and species without re- 

 gard, to size. From each otolith, after calibration of 

 an age model, the available information could in- 

 clude both fish length and age. This approach to 

 length data collection is not new and has been used 

 by the International Pacific Halibut Commission 

 for several years to estimate length (Southward 

 1962; Quinn et al. 1983). These techniques could 

 therefore streamline not only the collection of 



otoliths at sea but also the analysis of age in the 

 laboratory. 



The difficulty in age determination described 

 above and the resulting variability between 

 laboratories may have a negative impact upon ac- 

 curacy of fishery models, particularly those using 

 cohort or virtual population analysis (Brander 

 1974; Alverson and Carney 1975). The new 

 methodology can provide significant time and cost 

 savings over conventional methods and also de- 

 crease variability in age estimates. Implementa- 

 tion of these aging techniques, however, will re- 

 quire careful calibration with ages determined by 

 a consensus of expert otolith readers from all 

 management agencies with an interest in each 

 species for which a model is developed. 



ACKNOWLEDGMENTS 



This research was supported by Cooperative 

 Agreement No. 80-ABH-00049 from the North- 

 west and Alaska Fisheries Center, National 

 Marine Fisheries Service, NOAA, Seattle, Wash. I 

 thank Tom Dark, Mark Wilkins, and other partic- 

 ipants in the 1980 West Coast Survey for assis- 

 tance in specimen collection; particular thanks 

 are extended to Captains Bernie and Tom Hansen 

 of the FV Pat San Marie and MV Mary Lou, re- 

 spectively, and their capable crews. Technical as- 

 sistance and otolith reading were provided by 

 Mary Yoklavich, Dena Gadomski, and Robert 

 McClure. I thank Jack Lalanne for providing the 

 NMFS age estimates. Finally I thank W H. 

 Lenarz and D. R. Gunderson for critically review- 

 ing the manuscript. 



LITERATURE CITED 



Alverson, D. L., and M. J. Carney. 



1975. A graphic review of the growth and decay of popula- 

 tion cohorts. J. Cons. Int. Explor. Mer 36:133-143. 

 BAILEY, R. F. J., K. W. ABLE, AND W. C. LEGGETT. 



1977. Evidence for the presence of a metamorphic check in 

 capelin {Mallotus villosus) otoliths and implications for 

 age determination. J. Fish. Res. Board Can. 34:2008- 

 2014. 

 BEAMISH, R. J. 



1979a. Differences in the age of Pacific hake (Merluccius 

 productus) using whole otoliths and sections of 

 otoliths. J. Fish. Res. Board Can. 36:141-151. 

 1979b. New information on the longevity of the Pacific 

 ocean perch (Sebastes alutus). J. Fish. Res. Board Can. 

 36:1395-1400. 

 BENNETT, J. T, G. W. BOEHLERT, AND K. K. TUREKIAN. 



1982. Confirmation of longevity in Sebastes diploproa 

 (Pisces: Scorpaenidae) using ^"*Pb/"*Ra measurements in 

 otoliths. Mar. Biol. (Berl.) 71:209-215. 



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