398 



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Sampling date 



Figure 8 



Comparison of spawning time as determined by back-calculation from otoliths (A), maximum oocyte 

 diameter (Bl and histological stage (Cl for 1997. 



or adult fish were collected from the Big Bend; however, 

 these data also suggested a mid-summer spawning period. 

 Oocyte diameter and developmental stage data from the 

 Southwest indicated summer spawning (May to Septem- 

 ber) but because no adult gonads were collected earlier in 

 the year, a winter fertilization-date mode (as back-calcu- 

 lated from otoliths) could not be determined. 



Larval duration 



Presumed settlement marks were distinguishable in 

 some, but not all otoliths that were assigned ages. These 

 marks were identified by a sharper contrast than preced- 

 ing marks (Fig. 9). In addition, at this mark the increment 

 pattern changed abruptly, postsettlement increment 

 widths being consistently narrower than those laid down 



before settlement. Of the 135 otoliths collected during 

 1996 which were assigned ages, 80 (59%) had readily dis- 

 tinguishable settlement marks, whereas in 1997, 62 (64%) 

 had distinguishable marks. The estimated age at settle- 

 ment (planktonic larval duration) for 1996 and 1997 fish 

 ranged from 20 to 32 days (niean=25 days) and from 20 to 

 33 days (mean=24.7 days), respectively. ANOVA indicated 

 no significant sampling region or year effect or region- 

 and-year interaction on the age at settlement (planktonic 

 larval duration). 



In 1996, settlement first began in mid May in the Pan- 

 handle and continued throughout the summer, peaking 

 during the first week of August in the Panhandle and 

 Southwest, and ending finally on 1 October in the South- 

 west (Fig. 10). Results for settlement date data showed no 

 evidence for lunar periodicity in settlement, a chi-square 



