48 



Fishery Bulletin 91(1), 1993 



Figure 2 



Measurements on each opercle of Tautoga onitis used in age 

 analyses. Illustration depicts whole left opercle from Tautoga 

 onitis. Orientation of the opercle is: (A) anterior; (P) poste- 

 rior; (D) dorsal; (V) ventral. Successive annuli (3-15; first 

 two annuli obscured by articular apex) are indicated; OR is 

 the opercular radius; AA is the articular apex of the opercle. 



anterior to posterior margins of the bone were con- 

 sidered to be annuli and counted to determine age. 

 Other horizontal marks such as incomplete bands ( = 

 false checks) were not included in the annuli counts. 

 All annuli continuous within contours of the opercle 

 were counted on both right and left opercles using 

 transmitted light. Initially, annuli on both opercles 

 from each fish were counted with 90% agreement 

 between counts. If differences were noted, the age 

 estimate from the opercle with the most clearly de- 

 fined annuli was used. All age estimates were made 

 by the senior author, then a subset (n = 100) of those 

 opercles were re-read by the second author. All ini- 

 tial estimates by both readers were in agreement, 

 thus age estimates (by Hostetter) were used in sub- 

 sequent analyses. 



Annuli were counted for both right and left opercles 

 using transmitted light. A total of 24% (167/706) of 

 the opercles were counted six times; four counts were 

 made at lx and two were made at 6x magnifica- 

 tion. Since there was close agreement between all 

 counts regardless of magnification, the remaining 

 76% of opercles were aged twice under lx magnifi- 

 cation. Marginal increment, the seasonal growth of 

 the opercle, was measured by plotting increment 

 width from the last annulus (A) against date of cap- 

 ture (Fig. 3). 



Standard least-squares linear regression (Sokal & 

 Rohlf 1981) was used in Lotus-R spreadsheet format 

 (Jeanty 1984) to describe TL:SL, TL:OR, and TL:WT 

 relationships. Determination of time of annulus for- 

 mation was adopted from Nose et al. (1955) and Coo- 

 per (1967). Mean back-calculated TL-at-age (Table 1) 

 was computed for males and females separately and 

 for sexes combined, following Bagenal & Tesch ( 1978). 

 Slope and intercept values from these equations were 

 used in the back-calculated length equation of Ricker 

 (1975). Calculated lengths by sex were independently 

 determined through substitution of logarithmic val- 

 ues for average TL and OR by age-class. Analysis of 

 covariance (ANCOVA) using SPSS-X (Norusis 1985) 

 was used to compare age-at-length between sexes. 

 Back-calculated mean lengths-at-age were used to de- 

 velop von Bertalanffy curves (Gulland 1976). 



Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

 MONTH 



Figure 3 



Mean seasonal incremental growth (in mm I of opercles of 

 Tautoga onitis from coastal waters of Virginia. Vertical bars 

 represent the range; middle horizontal bars are the mean; 

 darkened portions represent the standard deviation; and num- 

 bers at top of each line are sample sizes. 



