Hostetter and Munroe Age. growth, and reproduction of Tautoga onitis 



49 



Table 1 



Back-calculation formulae for male and female Tautoga onitis 

 from coastal waters of Virginia (TL=mm total length; OR=mm 

 opercular radius I; L„=total length at year n; R n =opercle ra- 

 dius at year n; R,=opercle radius at capture; b=slope of 

 body-bone regression; where L n = log TL+b(log R„-log R,). 



(males) log TL = 1.2916+0.860 log OR (rc=398; r-'=0.968) 

 (females) log TL = 1.2889+0.864 log OR (n=281; r 2 =0.967) 



Results 



Ageing technique and validation 



Opercles were found to be the best structure for esti- 

 mating age of tautog. In fish with less than four an- 

 nuli, there was close agreement between annuli on 

 scales and those on opercles. However, abrasion, sur- 

 face-area damage, and ring compaction along the outer 

 margin of scales precluded using scales for ageing older 

 fish. Comparisons of age estimates from otoliths and 

 opercle bones from 27 fish indicated close agreement 

 in readings of annuli from each structure, especially 

 in younger fish. However, otoliths from larger fish had 

 a thickened nuclear core, which made it difficult to 

 discern any microstructure in this region. Sanding and 

 sectioning of otoliths proved difficult because of the 

 small size of the otoliths, and in most cases these pro- 

 cedures also blurred or removed annuli on the outer 

 edge of the otolith. The first annulus is also sometimes 

 difficult to detect on opercles of large tautog because of 

 thickening of the buttress zone at the articular apex. 

 In these instances (<5% of the fish aged), we assigned 

 a distance to the first annulus (7.4 mm) based on mean 

 measurements from opercles with clearly defined first 

 annuli. 



Opercle radius and TL (Fig. 4) were linearly related 

 (r 2 =0.97; sexes combined). Age estimates based on the 

 first and fourth readings (at lx ) of individual opercles 

 were in close agreement (81%, 135/167). All age dis- 

 agreements were within lyr (n=31), except one (2yr). 



Marginal increment analysis (Fig. 3) revealed mini- 

 mum growth distal of the last annulus during May, 

 June, and early July for all age-groups. There was no 

 indication of formation of a second mark during the 

 year for any fish examined. 



Age and growth 



A total of 712 tautog measuring 51-765 mm TL was 

 collected (Fig. 5). Of these, 701 (398 males, 282 fe- 

 males, and 21 immature fish of unknown sex) were 

 used to estimate age distribution and growth rates. 



100 200 300 400 500 600 700 800 

 TOTAL LENGTH (mm) 



Figure 4 



Relationship of opercular radius (OR) on total length (TL) for 

 Tautoga onitis (sexes combined) from coastal waters of Vir- 

 ginia. 1979-86. 



Specimens not included in age analyses had missing 

 data or damaged opercles, which precluded their use 

 in the analyses. Mature males (rc=364) ranged in size 

 from 198 to 765mmTL, weighed 138-6895 g, and were 

 aged 3-25yr. Mature females (n=247) were comparable 

 in size (232-750 mm TL) and weight (130-7392 g), and 

 were aged 3-21. Few males (9%, n=32) and females 

 (5%, n=14) in our samples were older than age-13. 

 Immature fish ranged from 51 to 265mmTL, weighed 

 5-410 g, and were aged 0-3 yr. Length-weight rela- 

 tionships (Figs. 6,7), calculated separately for males 

 and females, indicated that mean total lengths and 



