398 



Fishery Bulletin 90(2). 1992 



Annulus formation 



Evidence that checks are formed annually was obtained 

 by examining the index of completion at about 2-month 

 intervals throughout one season. The index of comple- 

 tion is a measure of the amount of bone growth since 

 the last check was formed, expressed as a proportion 

 of the previous growth increment. The indices of com- 

 pletion for fish aged 1-6 years were combined after 

 each age-group was observed to follow the same 

 seasonal changes in the index (Fig. 5). There were 

 significant (P< 0.001) differences in this index with 

 time of year for urohyals having one, two, three, four, 

 five and six checks (ANOVA, F 31.4, df 4, 172; F 80.1, 

 df 6, 246; F 100.7, df 6, 263; F 40.0, df 6, 141; F 15.5, 

 df 6, 69; F 88.8, df 5, 233, respectively). While there 

 was considerable variation in this index at any one 

 sampling period, there was a steady increase in the 

 mean index from October to August, followed by a 

 marked drop between August and October. It appears 

 that checks are laid down some time between August 

 and October. 



Bacl< -calculation 



Lengths were back-calculated to the last annulus, using 

 a proportional method based on the regression of fish 

 length on urohyal length— the body proportional 

 hypothesis (BPH) of Francis (1990). A quadratic equa- 

 tion best described the relationship between body 



ONDJ FMAMJ 



1982 



1983 



Figure 5 



Seasonal change in the index of completion (amount of bone 

 growth since the last check was formed) in Lutjamis inttus 

 urohyals with 1-6 checks. Individual indices are plotted against 

 day of sampling, and the line links the mean index for each 

 sampling period. 



10 15 20 



Urohyal length (mm) 



25 



Figure 6 



Curvilinear relationship between urohyal length and fish 

 length in Lutjanus I'itttis. 



length (L in mm) and urohyal length (U in mm) (Fig. 6): 



L= - 25.48 -H20.485U-0.193U2 (r2 0.95, df 1102). 



The mean absolute difference between using BPH 

 and SPH (regression of fish length on urohyal length) 

 was 1.6mm; BPH back-calculated smaller lengths in 

 fish <150mm and larger lengths in fish >200mm. 



Growth 



Von Bertalanffy growth curves were fitted to length- 

 at-age data for each sex separately. Fish whose sex 



