Laidig et al.: Age and growth of Sebastes mystinus 



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Methods 



Rockfish sampling 



Otoliths of blue rockfish were obtained from 1) the rec- 

 reational catch of commercial passenger fishing vessels 

 (CPFV); 2) the catches of midwater trawls deployed from 

 a research vessel; and 3) specimens speared by research- 

 ers equipped with SCUBA (Table 1). CPFV landings were 

 available from Monterey to Bodega Bay, California, from 

 1978 to 1998. All fish were caught at depths deeper than 

 20 m; total length (TL) and sex were recorded for each spec- 

 imen, and otoliths were removed. Pelagic young-of-the-year 

 blue rockfish were caught in a 13 x 13 m midwater trawl 

 deployed periodically from the RV David Starr Jordan off 

 the central California coast from Monterey to Marin coun- 

 ties during 1988-93 at depths of 5-30 m. In the laboratory, 

 each specimen was measured (standard length [SL]) and 

 otoliths were removed and attached to microscope slides for 

 later examination. Specimens were taken with spears from 

 1988 to 1998 in water depths of 1-20 m off Sonoma and 

 Mendocino counties (Table 1). Some cohorts were sampled 

 throughout their first year after first settlement, thus pro- 

 viding specimens of known age. We measured each speci- 

 men, determined sex, and removed otoliths. All fish lengths 

 (either TL or SL) were standardized to PL for comparisons 

 (by using equations from Echeverria and Lenarz, 1984). 



Otolith examination 



Ages were estimated by counting the number of translu- 

 cent zones from the surface of whole otoliths for young 

 blue rockfish (less than 5 years of age) and by using the 

 break-and-burn method (Chilton and Beamish, 1982) for 

 fish greater than 5 years old. Whole otoliths were viewed 

 through a dissecting microscope at 20-40x magnifica- 

 tion with refiected light. For the break-and-burn method, 

 whole otoliths were broken in half through the core, and 

 one broken section was burned and viewed through a dis- 

 secting microscope at 20-40x magnification. Two readers 

 determined ages independently by counting the number 

 of translucent zones observed in both whole and broken- 

 and-burnt otoliths. The precision of age estimates was com- 

 pared by using the average percent error (APE; Beamish 

 and Fournier, 1981). Otolith diameter was measured from 

 the dorsal to the ventral edge through the core of the oto- 

 lith. The diameter of the otolith at each presumed annual 

 growth increment was measured from a video image of 

 the cross section of a broken section of the otolith from 

 the dorsal edge to the ventral edge of the translucent zone 

 along a transverse axis through the core. 



Validation of growth increments 



Validation of growth increments as being produced annu- 

 ally was conducted in four parts. First, we conducted an edge 

 analysis (Pearson, 1996) to determine if only one translu- 

 cent zone formed along the edge of the otolith during a year. 

 We identified the leading growth edge as either "opaque" 

 or "translucent" on otoliths collected throughout the year 



to determine when the translucent zone was formed. An 

 examination of edge analysis data was conducted on each 

 age class from 1 to 44 years to determine if only one opaque 

 and one translucent zone formed annually, and if they had 

 formed, then these ages were considered validated. 



Second, to identify the first annual growth increment, 

 the average diameter of otoliths from known age one-year- 

 old fish was compared to the average diameter of the first 

 translucent zone from older fish. We determined the length 

 of one-year-old fish at the time of translucent zone comple- 

 tion (as determined by the edge analysis) by plotting fish 

 length against Julian date of capture and then determined 

 the best model that described this relationship. 



Third, we determined the predicted otolith diameter of 

 a fish at the time of translucent zone completion. For this 

 analysis, we used fish lengths from young-of-the-year ( YOY; 

 both pelagic and settled) and one-year-old blue rockfish for 

 which ages were known by following a cohort through time. 

 Fish length was plotted against total otolith diameter, and 

 the best model for this relationship was determined. Using 

 this relationship and the size of a one-year-old fish (es- 

 tablished from the previous model), we calculated otolith 

 diameter for one-year-old fish. 



Fourth, mean diameters of the first, second, and third 

 translucent zone of all otoliths from older fishes were 

 measured. The diameters of these three translucent zones 

 were compared to each other by using a Student's t test. If 

 the first translucent zone corresponded to the diameter of 

 an otolith at the time of completion of the first translucent 

 zone and the first translucent zone was significantly differ- 

 ent from the second and third zones, then the assumption 

 that the first translucent zone was equivalent to the first 

 annual growth increment was considered validated. 



