Dentzau and Chittenden: Population dynamics of Polydactylus octonemus in the Gulf of Mexico 



443 



Figure 4 



Length frequencies of immature ani:l female Polydactylus octotiemiis 

 by gonad stage. 



Figure 5 



Percentage of mature female Polydactylus octonemus as a function 

 of size. 



dard, fork, and total lengths used regressions pre- 

 sented herein. 



presented were termed apparent, because they may 

 have been affected by recruitment of larger young from 

 estuaries to the Gulf, by emigration and/or gear 

 avoidance of fish about age I, or by a change from 

 demersal to pelagic behavior; if so, they overestimated 

 mortality, K, and spawning period durations and 

 underestimated life spans, maximum sizes, average 

 sizes at age, and L^. 



Von Bertalanffy parameters were calculated using 

 Fabens' (1965) program and the same data used in TL 

 on age regressions (Fig. 2). These points described a 

 curvilinear regression and evidenced an asymptote, so 

 they met the minimum requirements for a von Berta- 

 lanffy fit (Knight 1968, Gallucci and Quinn 1979). Un- 

 less stated, all length frequencies were moving aver- 

 ages of three and all lengths were total length. The 

 symbol "?L" was used for instances where the type of 

 length was not reported. Conversions between stan- 



Results 



Maturation and spawning periodicity 



Polydactylus octonemus begin to mature at 165-210 

 mm in late summer-early fall. Sex usually could be 

 determined by eye at 165 mm as many females entered 

 the Early Developing stage (Fig. 4). Fish entered later 

 stages at 180-210 mm. M50 was 185-195 mm, about 

 7-9 months old (Fig. 5), in agreement with gonad-stage 

 length frequencies. 



Little somatic growth seemingly occurs after P. oc- 

 tonemus enter later stages of gonad development. 

 Mean sizes were 188 mm in the Early Developing stage 

 (Fig. 4), 197 mm when Late Developing, and 196 mm 

 when Gravid. The only fish collected in the Spawn- 

 ing/Spent stage was 189 mm. Minimum and maximum 

 sizes remained constant after the Early Developing 

 stage. 



