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



345 



90 J 

 80 -- 

 70-- 

 60-- 

 S 50-- 



I 40-- 



30 ■- 

 20 - 

 10-- 







FEMALES: (f = 10"'" (7l"") 

 MALES: W = XO'^'" (TL"^'^ 



^^ 



 Males 

 A Females 



200 



250 



Total length (mm) 



Figure 3 



Total length-weight relationship for both sexes of blackcheek tonguefish, Symphurus 

 plagiusa, from lower Chesapeake Bay and major lower tributaries. 



formation, the densely compacted opaque zone 

 delimiting the annulus was easily identifiable. The 

 combination of one broad translucent zone and one 

 narrow opaque zone (Fig. 5) represents one year's 

 growth. 



Otolith maximum diameter (OMD) was linearly 

 related to total length (Fig. 6) and described by the 

 following relationship: 



TL = 64.59(OMD)- 17.02. 



[r2=0.93] 



This linear relationship indicated that otolith growth 

 was proportional to fish growth. 



Size at first annulus formation for blackcheek 

 tonguefish ranged from 88 to 138 mm TL (mean 

 length ca. 118 mmTL). Seasonal progression of modal 

 length frequencies (Fig. 7) for young-of-the-year fish 

 (YOY) corroborated first-year growth-rate estimates 

 determined from annular marks on the otoliths. 

 Pooled data for 1993-96 from VIMS^ trawl survey 

 reports indicated that YOY blackcheek tonguefish 

 recruited to the gear during September, usually at 

 sizes of ca. 35-45 mm TL. By the following June, 

 these fish had reached sizes ranging from ca. 53 to 

 138 mm TL. Thus, empirical data from length fre- 



' VIMS (Virginia Institute of Marine Science I. Department of 

 Fisheries, Gloucester Point, VA 23062. Unpubl. data. 



quencies agreed fairly well with first-year growth 

 estimates derived from interpretation of annulus for- 

 mation on the otoliths. 



Monthly mean marginal increments on the otoliths 

 were plotted for fish from all age groups (Fig. 8). The 

 seasonal progression of marginal increments was 

 similar on otoliths from all age groups; therefore, data 

 were pooled to demonstrate general trends in annual 

 growth. Marginal increments were smallest during 

 June of both 1994 and 1995. Monthly mean marginal 

 increments showed only one trough during a year, 

 indicating that a single annulus is formed yearly in 

 June. In 1994, margin width on the otoliths increased 

 rapidly during July and August, reflecting an active 

 period of growth. After August 1994, margin width 

 leveled off and remained fairly constant from Sep- 

 tember 1994 through May 1995. Large variation (in- 

 dicated by high standard error) for samples taken 

 during May of both 1994 and 1995 may indicate that 

 the season of annulus formation may be somewhat 

 more protracted (May-June) and perhaps dependent 

 upon environmental factors. Alternatively, it may 

 simply reflect an artifact of the small sample sizes 

 examined from this period. 



Mean lengths at age were backcalculated for 92 

 males and 145 females (Table 2). Remaining fish were 

 young-of-the-year and therefore were excluded from 

 this analysis. Observed (empirical) lengths were con- 



