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Fishery Bulletin 100(3) 



There was evidence of multiple cohorts in the 

 Southwest in October 1996 and in April 1997. Ju- 

 veniles collected in 1997 (mean=88.3 mm SL) were, 

 on average, about 50% larger than those collected in 

 1996 (mean=59.9 mm SL). Fish collected from the 

 Southwest were also larger on average than those 

 from the Panhandle both years. 



Age and growth 



Increments in the lapillus occurred at regular inter- 

 vals and a consistent width and marked contrast 

 was evident between each one. More closely spaced 

 increments occurred at irregular intervals with less 

 contrast between them. Usually we counted fewer 

 increments in sagittae than in lapilli. Lapilli were 

 thinner and flatter than sagittae and therefore 

 required less grinding and could be examined whole, 

 whereas sagittae had to be sectioned first. Incre- 

 ments near the edge of the lapilli were also clearer 

 and easier to distinguish compared with those from 

 sagittal sections. Increment counts were success- 

 fully assigned to 137 (71%) of the juveniles collected 

 in 1996 and 97 (82%) of the 1997 collection. Uncor- 

 rected increment counts ranged from 35-128 (mean=75) 

 in 1996 and 50-226 (mean=125) in 1997. 



Several lines of evidence suggested that increments 

 were deposited daily. The linear regression of SL (mm I 

 on lapillus length (jam) indicated a highly significant re- 

 lationship between body size and otolith size for fish col- 

 lected in 1996 (P<0.000, r2=0.97) and 1997 fP<0.000, r- = 

 0.96). Juveniles selected for the otolith marking experi- 

 ment ranged from 31.4 to 44.6 mm SL (mean=38.4 mm, 

 standard error=0.63 mm). Only 21 out of 30 surviving 

 alizarin-complexone-marked juveniles had otoliths with 

 visible marks and no fish harvested on day 21 had read- 

 able marks. Mean growth rate for survivors was estimat- 

 ed at 0.33 mm/d. The slope (6=0.87) of the regression 

 of the number of increments counted after the alizarin 

 mark on the number of days juveniles were held after 

 marking was not significantly different from 1.0 (Fig. 41 

 (^test, P<0.05); therefore we did not reject the hypoth- 

 esis that increments were deposited daily. 



Instantaneous daily growth of juvenile snapper was 

 1.02 mm/d in 1996 compared with 0.60 mm/d in 1997 ( Fig. 

 5). AN OVA indicated a significant difference in slopes 

 (i.e. growth rates) between years (P<0.001). However, 

 ANCOVA indicated that there was no significant differ- 

 ence in growth rate among regions. Because there was a 

 significant difference in standard lengths between years 

 and regions, only those size ranges that overlapped be- 

 tween the two regions (i.e. Panhandle and Southwest, 

 1996: 29-83 mm SL, 1997: 39-112 mm SL) and between 

 years (i.e. 32-110 mm SL) were included in the analysis. 



Fertilization-date distribution 



There were distinct patterns in the temporal and spatial 

 distribution of fertilization dates. Our results however 

 provided little support for lunar periodicity in spawn- 



7 14 21 28 



Days after mark 



Figure 4 



Linear regression of increment count on number of days after 

 alizarin marking of the lapillus. 



ing. Back-calculated fertilization dates indicated that 

 surviving juveniles in the Panhandle and Big Bend were 

 mainly summer spawned fish, whereas Southwest juve- 

 niles had winter and summer fertilization dates. In 1996, 

 the earliest back-calculated birth date was 25 February 

 from a fish from the Southwest, although a few (i.e. six 

 fish) were recorded from late April and early May from 

 the Panhandle and a few more by mid-May from the 

 Southwest (Fig. 6). Most fish spawned beginning in mid- 

 June and a peak in fertilization dates occurred during 

 mid-July for both regions. Frequency of spawning then 

 declined and the latest fertilization date of the year was 

 recorded in mid-September from the Southwest. A chi- 



