FISHERY BULLETIN: VOL^ 79, NO. 4 



LATE SUMMER GROUPS SPRING GROUPS 



SEP 



aMa AvyfcA A c^ 



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OCT 



NOV 



A^ M A A^ 



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DEC 



A/\ A A 



20 40 60 80 



-A^M^ 



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-I 1 — '-' — r 1 



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20 40 60 80 



MARGINAL INCREMENT (MMx42) 



Figure 14. — Monthly marginal increments for Cynoscion are- 

 na mis with one mark. 



sis, because annulus formation occurs over a broad 

 time period in both spring and late summer 

 groups. Exact age determination may be impossi- 

 ble for the apparently few fish older than say, age II 

 or III. Their ages probably would not be distinct in 

 length frequencies and a spawned group probably 

 could not be assigned. 



Causes of annulus formation in C. arenarius are 

 not clear, although temporary growth cessation 

 may be associated with movements between es- 

 tuaries and the gulf and/or gonad development. 

 Annulus formation in late summer fish coincides 

 with their spring movement to estuaries and 

 gonad development. Similarly, annulus formation 

 in spring fish coincides with fall movements from 

 estuaries. However, many spring fish use only gulf 

 nurseries in their early life which might minimize 

 mark formation in those fish. False annulus for- 

 mation might be associated v/ith movements be- 

 tween estuaries and the gulf. Cynoscion arenarius 

 and C. regalis are similar in that both migrate 

 between the sea and estuaries ( Welsh and Breder 

 1923; present studies) and their scales exhibit 

 many false annuli (Merriner 1973; present 

 studies). In contrast, C. nothus, a gulf resident, 

 exhibits few false annuli { DeVries and Chittenden 

 footnote 6). 



MAXIMUM SIZE, LIFESPAN, 

 AND MORTALITY 



with their sizes at age in spring and early sum- 

 mer (Figures 4, 5). 



Repeated examination suggests that age deter- 

 mination was consistent. We found 86% agree- 

 ment in a second reading of scales from 361 fish 

 120-338 mm TL, including all fish initially deter- 

 mined to have an annulus. Disagreement occurred 

 primarily when the scales had a mark close to the 

 margin or had one annulus and one false annulus. 



Discussion 



Scales can be used to age C. arenarius, but 

 length-frequency analysis is simpler and at least 

 as accurate except possibly with fish much older 

 than those we caught. Separate spring and late 

 summer spawning periods complicate age deter- 

 mination. Age, growth, and mortality estimates 

 should be based on individual spawned groups to 

 avoid misinterpretation. Valid estimates require 

 assignment of individuals to correct spawned 

 groups; and that requires length-frequency analy- 



Cynoscion arenarius is small and short lived. 

 The largest of the 13,780 fish we captured was 342 

 mm TL, although few exceeded 300 mm. Our find- 

 ings agree with Gunter (1945), Hildebrand (1954), 

 Perry (1970), and Chittenden and McEachran 

 (1976) who captured fish to 377 mm TL but few 

 >300 mm. Many other studies have reported even 

 smaller maxima including Miller (1965), Christ- 

 mas and Waller (1973), and Perret and Caillouet 

 (1974). The only published records much >300-375 

 mm TL include a few trawl-caught fish 425-497 

 mm TL from the north-central gulf (Franks et al. 

 1972; Adkins and Bowman 1976) and off Texas 

 (Mohsin 1973), 590 and 540 mm TL gill net caught 

 fish from northwestern Florida (Vick 1964; Trent 

 and Pristas 1977), and fish as large as 483 and 503 

 mm TL captured in Galveston Bay, Tex., by com- 

 mercial and recreational fishermen, respectively 

 (Heffernan et al.'^). The latter study gave size data 



'Heffernan, T. L., A. W. Green, L. W. McEachron, M. G. 

 Weixelman, P. C. Hammerschmidt, and R. A. Har- 

 rington. 1976. Survey of finfish harvest in selected Texas 



662 



