FISHERY BULLETIN. VOL. 79, NO. 4 



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GROWTH PERIODS 



Figure ll. — Monthly growth increments of Cynoscion arenar- 

 lus for spring and late summer groups from the Gulf of Mexico. 

 Unadjusted well-defined increment data of Shlossman ( 1980, 

 tables 1,2) were converted to growth per 30 d. Increments with 

 a diagonal (/) reflect movement, not necessarily low growth. 

 Negative increments were rounded to zero. 



Female C. arenarius reach larger sizes than 

 males. All fish >300 mm TL (n = 13) and 887f 

 examined >250 mm (n = 80) were female. 



Discussion 



Our findings on C arenarius growth agree with 

 the limited literature. Our average growth 

 estimates — 210-280 mm TL at age I depending 

 upon the spawned group — agree with data of Fer- 

 ret and Caillouet (1974, fig. 6), but slightly exceed 

 data of Swingle and Bland (1974:41) and estimates 

 of Hoese etal.( 1968), McEachronetal.( 1977), and 

 Chittenden (1977). Decreased growth in winter 

 agrees with observations of Gunter (1945) and 

 Hoese et al. (1968). Seasonal growth is similar to 

 that of C nothus (DeVries and Chittenden foot- 

 note 6), C. nebulosus (Pearson 1929; Tabb 1961), 

 andC. regalis (Welsh and Breder 1923; Hildebrand 

 and Cable 1934; Merriner 1973). However, C. 

 arenarius is larger at age I than its three congen- 

 ers in the western North Atlantic: 1) C. nothus, 

 130-190 mm SL = 158-229 mm TL (DeVries and 

 Chittenden footnote 6); 2) C. regalis, 143-180 mm 



SL = 173-218 TL (Taylor 1916 in Merriner 1973; 

 Perlmutter et al. 1956; Merriner 1973); and 3) C. 

 nebulosus, 116-165 mm SL = 144-201 mm TL 

 (Pearson 1929; Moody 1950; Klima and Tabb 1959; 

 Moffett 1961; Tabb 1961). Our findings that 

 females grow larger than males has been reported 

 (Franks et al. 1972), and similar differences occur 

 in C. nebulosus (Pearson 1929; Klima and Tabb 

 1959; Tabb 1961). 



AGE DETERMINATION USING SCALES 



General Basis 



Cynoscion arenarius can be aged using scales. 

 Annuli were identified using standard criteria 

 (Tesch 1971) and procedures for C. nebulosus, C. 

 nothus, and C regalis (Klima and Tabb 1959; Tabb 

 1961; Merriner 1973; DeVries and Chittenden 

 footnote 6l. Characters used to identify annuli in- 

 cluded: 1) a clear zone between bands of circuli in 

 the anterior field (Figures 12, 13), 2) a band of 

 crowded circuli adjacent to a band of more widely 

 spaced circuli (Figure 12), 3) secondary radii 

 radiating from a clear zone or changed spacing 

 between circuli (Figures 12, 13), 4) cutting over of 

 circuli (Figures 12, 13), and 5) appearance of these 

 characters on all or most scales. Marks identified 

 as false annuli: 1) appeared on only a few scales 

 from a fish, 2) had secondary radii not accom- 

 panied by a clear zone or changed spacing of cir- 

 culi, 3) had a clear zone or changed spacing 

 between circuli not accompanied by other char- 

 acters, and 4) lacked distinct cutting over. False 

 annuli were common, as Merriner (1973) found 

 for age and age I C. regalis. 



Results 



Few fish had scales with an annulus. Only 159 of 

 1,602 fish (10%) examined had one annulus and 

 only 6 fish ( 0.4% ) had two annuli. This finding that 

 10% had one annulus is not consistent with the 

 99% annual mortality rate reported later. How- 

 ever, the sample aged was biased by arbitrary 

 selection of large fish. Moreover, the annulus 

 primarily forms at 0.5-0.75 yr which is before an- 

 nual mortality is complete. 



The first annulus forms from April through 

 November, although spring and late summer 

 spawned fish may form annuli at different times. 

 Marginal increments in late summer fish were 

 smallest in spring and early summer (Figure 14), 



660 



