Terwilliger and Munroe: Age, growth, longevity, and mortality of Symphurus plagiusa 



343 



otolith with the OPRS. The average margin 

 width, i.e. the translucent region between the 

 last annulus and the proximal edge of the 

 otolith, was plotted by month. 



Regression analyses of otolith maximum di- 

 ameter on total length and of weight on total 

 length were calculated by the method of least 

 squares. Back-calculated lengths-at-age were 

 computed by using the Lee method (Lagler, 

 1956). To evaluate growth, back-calculated 

 lengths-at-ages were fitted to the von Berta- 

 lanffy model (Ricker, 1975) by using nonlin- 

 ear regression ( Marquardt method ) calculated 

 with Fishparm computer software (Saila et al., 

 1988). Likelihood-ratio tests were used to com- 

 pare parameter estimates of the von Berta- 

 lanffy equation for males and females (Ki- 

 mura, 1980; Cerrato, 1990). 



A scale sample from a region in the poste- 

 rior third of the body, dorsal to the midline, 

 was taken from all fish. Six scales from each 

 fish were cleaned with hydrogen peroxide and 

 mounted on plastic strips by using a Carver 

 hydraulic laboratory press. A random sample 

 of scale strips from 50 fish were then viewed 

 with a microfiche reader in order to discern 

 annuli for comparison with otolith sections. In 

 contrast to otoliths, scales proved to be unre- 

 liable for ageing this species. Annuli were 

 poorly defined and difficult to distinguish, and 

 in many cases, the scales were unreadable. 

 Fish ages obtained from scales agreed with 

 ages obtained from otoliths in only 12% of the 

 cases. This is not surprising, because scale 

 annuli from other fish species with known ages 

 have been shown to be inconsistent indicators 

 of age, even in relatively young fish (Prather, 

 1967; Heidinger and Clodfelter, 1987). 



Instantaneous total annual mortality rates, 

 Z, were estimated from maximum age esti- 

 mates with a pooled regression equation as 

 suggested by Hoenig (1983) and by calculat- 

 ing a theoretical total mortality for the entire 

 lifespan following the reasoning of Royce 

 (1972) as described in Chittenden and 

 McEachran ( 1976 ). Values of Z were converted 

 to total annual mortality rates. A, using the 

 relationship A = 1 -e"^ (Ricker, 1975). 



Results 



A total of 566 fish, encompassing a size range from 

 36 to 202 mm TL (Fig. 2A), were used in this ageing 

 study. This size range included individuals from all 



c 

 m 



3 

 <D 



160 

 140 ■• 

 120  • 

 100 ■• 



40 •■ 



-I — I — I — I — I — I — I — I — I — I — 1^ 



Total length (mm) 



Figure 2 



Length-frequency distribution for blackcheek tonguefish, 

 Symphurus plagiusa: (A) length frequency for blackcheek 

 tonguefish from lower Chesapeake Bay and major lower tributar- 

 ies for fishes aged in this study; (Bl length frequency for blackcheek 

 tonguefish caught by Virginia Institute of Marine Science's juve- 

 nile fish recruitment trawl survey in lower Chesapeake Bay and 

 major lower tributaries, 1993-1996; (C) length frequency for 

 blackcheek tonguefish caught at the mouth of Chesapeake Bay 

 and inner shelf off Virginia and North Carolina, 1987-89. 



life history stages from postsettling juveniles to ma- 

 ture adults. The sex ratio for blackcheek tonguefish 

 collected in this study was 223 males:343 females, 

 or 1:1.54. AG-test of the sex ratio for 566 blackcheek 

 tonguefish indicated statistically significant devia- 

 tions (G=:25.64; df=l; P<0.001) from a 1:1 sex ratio 

 (Table 1). A G-test of sex ratios for blackcheek 



