346 



Fishery Bulletin 97(2), 1999 Iwl 



sistently higher than the back-calculated lengths-at- 

 age for individual age groups, which indicated that 

 seasonal growth had occurred since formation of a 

 new annulus. Differences between back-calculated 

 lengths-at-age and observed lengths are in the range 

 of observed seasonal growth. Males and females have 

 similar lengths-at-age until age 4 (Table 2). Beyond 

 age 4, mean lengths for females were slightly greater 

 than those for males. The largest male collected in 

 this study was 190 mm (age 5+); the largest female 

 collected was 202 mm (age 5h-). 



Greatest incremental growth in TL for both sexes 

 occurred during the first year and then declined rap- 

 idly thereafter (Table 2). Mean back-calculated 

 lengths for females and males at the end of their first 

 year were 78.84 mm and 75.68 mm, respectively. 

 Growth for both sexes in the second year was only 



■•- <M cn 



■^ K 



8 ? 



04 rsi 



100 



Total length (mm) 



Figure 4 



Length at maturity for blackcheek tongucfi.sh, Symphurua 

 plagiuna. in lower Chesapeake Bay and major lower tributarie.s: 

 lA) females; (B) males. Arrow represents length at .'509; maturity. 



39—41% of that recorded for the first year. Growth 

 increments continued to decrease every year there- 

 after for both sexes until age 5, when the estimated 

 growth increment increased slightly for both sexes. 

 This increase at age 5 may be an artifact due to the 

 relatively small number of samples for both sexes in 

 this age group. 



Length frequency for blackcheek tonguefish caught 

 by VIMS- trawl survey (1993-96) shows a bimodal 

 distribution (Fig. 2B), but this distribution does not 

 adequately reflect age composition of the individu- 

 als, especially for fishes larger than 110 mm TL. 

 Despite the bimodal distribution in length frequen- 

 cies, six age groups are represented in this distribu- 

 tion, and much overlap in total length exists between 

 age groups, especially those consisting of medium- 

 and large-size fish. These data indicate that length 

 frequency analyses are unreliable age estima- 

 tors for older individuals of this species. 



Von Bertalanffy parameters were computed 

 (Table 3) by using lengths backcalculated to 

 the most recent annuli to reduce bias in as- 

 ymptotic length and growth coefficient K due 

 to the presence of Lee's phenomenon in the 

 back-calculated lengths-at-age (Vaughan and 

 Burton, 1994). The growth coefficient K for 

 female blackcheek tonguefishes (0.320) was 

 greater than that (0.285) calculated for males. 

 Males and females achieved 50% of L , by the 

 end of their first year and 759^^ between ages 2 

 and 3 (Fig. 9). Results of likelihood-ratio tests 

 (Table 4) showed no significant differences in the 

 overall von Bertalanffy growth models for males 

 and females (x^=6.56, df=3, P=0.09). Estimates 

 of L . (x^=0.10, df=l, P=0.75), K (/2=o.03, df=l, 

 P=0.87l, and^,)(x2=0.19, df=l,P=0.67)werenot 

 significantly different between sexes. 



Values for asymptotic lengths for both sexes 

 agreed well with observed lengths. The larg- 

 est male collected in this study was 190 mm 

 and the calculated L^ for males was 196.5 mm. 

 The largest female collected in this study was 

 202 mm and the calculated asymptotic length 

 for females was 190.6 mm. These results are 

 acceptable because asymptotic length is a re- 

 gression estimate, and thus an average that 

 represents an average maximum length if fish 

 live and grow according to the von Bertalanffy 

 equation. Nevertheless, the overall estimated 

 asymptotic length value (192.4) represents a 

 reasonable approximation of the average maxi- 

 mum length estimate for the species. 



^ VIMS, Department of Fisheries, Gloucester Point, VA 

 23062. Unpubl. data. 



