Fischer et al.: Age, growth, mortality, and radiometric age validation of Lut/anus gnseus 



313 



highest in 1973 and exhibited a steady decline to a low 

 in 1995. 



The periodicity of opaque annulus formation in gray 

 snapper otoliths was further examined by plotting the 

 monthly percentages of otoliths with opaque margins 

 (Fig. 4). Although little data were available for the win- 

 ter months, one specimen sampled in January and two 

 specimens sampled in February 2001 each exhibited 

 opaque marginal otolith edges indicating that opaque 

 annulus formation occurs during the winter. Minimum 

 percentages of otoliths with opaque margins during 

 the months of April (22%) and May (8%) followed by 

 an absence of opaque margins during the months of 

 June through October indicate the cessation of opaque 

 annulus formation by early spring and the onset of 

 translucent annulus formation beginning in April and 

 continuing through November. 



Male and female gray snapper ranged in age from 1 

 to 28 years (Fig. 5A). There was no significant differ- 

 ence in age distributions between males and females 

 (maximum difference=6.92 yr), but both sexes exhibited 

 variable multimodal distributions in age frequency. 



Year of birth (YOB) frequency was also multimodal, 

 and the population was dominated by younger fish; 77% 

 of males and 80% of females were aged at 10 years or 

 younger (Fig. 5B). 



Significant differences in slopes were detected when 

 plotting age-W relationships between sexes (ANCOVA 

 test of homogeneity of slopes, F 3 353 = 8.06; P=0.0005). 

 Therefore, predictive models of age-W were fitted sepa- 

 rately for males and females using a power function 

 with least squares as (Fig. 6) 



Male age = 0.0278 (W ) 106 



(F 2 204 =3,956.29, P<0.001, r 2 =0.89). 



Female age = 0.0460 (W o ) 097 



(F 2 148 =4,504.05, P<0.001, r 2 =0.90). 



The single von Bertalanffy growth model to describe 

 gray snapper TL at age (Fig. 7) was 



L t = 656.4(1 - e l-0-22inj| 



<F 2 714 = 32,217.6; P<0.0001; r 2 =0.72). 



