(1979b) estimated ages approaching 90 yr in cer- 

 tain Pacific species of Sebastes, including S. 

 alutus. In the genus Sebastes, these estimates of 

 extended longevity have recently been confirmed 

 by Bennett et al. (1982), who used geochronologi- 

 cal methods to confirm age in S. diploproa. Under- 

 standing population structure for such long-lived 

 species will require a large number of age esti- 

 mates using otolith sections. Routine sectioning 

 and interpretation of otoliths, however, is a time- 

 consuming process, and age structure would need 

 to be determined frequently for management of an 

 active fishery. In this paper I suggest a possible 

 alternative method for age determination. 



Otolith growth begins with the initial "focus" 

 and thereafter by incremental concretions of cal- 

 cium carbonate in the form of aragonite. Otolith 

 size increases with increasing size and age of the 

 fish. Differential addition of crystalline material 

 to the otolith, however, results in a species-specific 

 shape (Bingel 1981). In flatfish and certain other 

 species, Williams and Bedford (1974) observed con- 

 tinued linear growth of the otolith with growth of 

 the fish only until maximum size was achieved; 

 beyond this time, the otolith began to thicken. 

 This has been observed in several other species 

 (Blacker 1974a). Linear measurements of the 

 otolith (i.e., length and width) are directly related 

 to fish length and show little variability, but 

 otolith thickness and weight are highly variable 

 in larger fish (Templeman and Squire 1956; 

 Beamish 1979a, b). 



Templeman and Squire (1956) observed that 

 length and width of otoliths from slow- and fast- 

 growing populations of haddock did not differ at 

 the same fish length, whereas otolith weight was 

 consistently greater in the slower growing (and 

 therefore older) populations at a given length. The 

 same trend appears to exist in some members of 

 the genus Sebates (G. W. Boehlert unpubl. data). 



Beamish (1979a) observed an increase in thick- 

 ness of the hake otolith with increasing otolith 

 section age and a nearly linear relationship of 

 otolith thickness and otolith weight. If otolith 

 thickness, and therefore weight, is a function of 

 fish age, then if fish length (or otolith length, since 

 the two are related) is known, one should be able to 

 estimate fish age. This was suggested by Brander 

 (1974) with Irish Sea cod. The objective of this 

 study is to determine the trends of otolith growth 

 in terms of thickness, length, width, and weight, 

 and to determine the potential of these criteria for 

 estimation of age in splitnose rockfish, S. diplop- 

 roa, and canary rockfish, S. pinniger. 



FISHERY BULLETIN: VOL. 83, NO. 2 



MATERIALS AND METHODS 



Otolith Collection 



Otoliths of S. pinniger and S. diploproa were 

 collected during the 1980 West Coast Survey con- 

 ducted by the Northwest and Alaska Fisheries 

 Center on the FV Pat San Marie and the FV Mary 

 Lou. Gear and sampling strategy were similar to 

 that described in Gunderson and Sample (1980). 

 Otoliths were collected from fish captured in all 

 hauls until desired numbers of specimens in 

 specified length categories were obtained. Both 

 otoliths from each specimen were removed, 

 cleaned, and stored in individual, labeled vials 

 containing 50% ethanol. Data taken with each 

 specimen included vessel, haul (with latitude, lon- 

 gitude, and bottom depth), sex, and fork length 

 (to the nearest 0.1 cm). After returning to the 

 laboratory, otoliths were thoroughly cleaned and 

 the preservative renewed. 



Age Determination 



General information on otolith morphology and 

 whole otolith aging methodology in Sebastes is 

 described in detail by Kimura et al. (1979). Age 

 determined from whole otoliths followed the aging 

 methodology of Boehlert (1980) for S. diploproa 

 and that of Six and Horton (1977) for S. pinniger. 

 Ages determined in this manner are referred to as 

 whole otolith ages. 



Otolith sections were prepared for selected 

 specimens using the left otolith after the 

 methodology of Nichy^ with several modifications. 

 Specimens were affixed to heavy-duty cardboard 

 tags with double-faced tape and embedded in 

 polyester casting resin in preparation for section- 

 ing. Specimens were mounted in a chuck specifi- 

 cally designed to accommodate the cardboard tags 

 and fed onto a pair of thin diamond blades sepa- 

 rated by acetate spacers on a Buehler** low-speed 

 Isomet saw. Dorsal-ventral sections through the 

 focus and perpendicular to the sulcus, about 0.4 

 mm thick, were removed from the center of the 

 otolith. Sections were removed from the tag and 

 attached to labeled microscope slides with his- 

 tological mounting medium. They were sub- 

 sequently ground to eliminate surface artifacts, 



'F. Nichy, Northeast Fisheries Center Woods Hole Laboratory, 

 National Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543. 



■* Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



104 



