BECKMAN ET AL.: AGE AND GROWTH OF RED DRUM 



Figure 5.— Age-frequency distributions for red drum captured 

 October 1985-September 1986 and October 1986-September 1987 

 by purse seine from offshore northern Gulf of Mexico waters. 



and by weight: 



males: W, = 10,548(1 - e-«"'^('*8.69))3_ 

 females: W, = 15,207(1 - e-o.o79«.ii.57))3 



of-birth distributions (Fig. 6). Variability in year- 

 class success is suggested by differences in relative 

 numbers of individuals between year classes. 



The separation of sexes in growth models resulted 

 in a significantly better fit by weight (P < 0.001) and 

 length (P < 0.001) when compared with models in 

 which sexes were combined. Separate von Berta- 

 lanffy growth curves best described changes in 

 length (Fig. 7A) and weight (Fig. 7B) of red drum. 

 Equations by length were 



males: L, = 909(1 - e-o.i37((..7.74)) 

 females: L, = 1,013(1 - e-o.o88<(.ii.29)) 



DISCUSSION 



Sampling 



Comparison of length-frequency distribution be- 

 tween gear types demonstrated that gill net and 

 hook and line were different from purse seine 

 collections. Therefore, to provide a basis for docu- 

 menting and comparing age structure in the off- 

 shore schooling population only purse seine collec- 

 tions were used. We assumed that purse seine 

 samples would result in the smallest size selection 

 bias (Nielson and Johnson 1983). We assumed 

 that temporal and spatial bias was minimized 

 because sets were made throughout the year and 



cvjrO'j-LOaar^ooaiO'— cNfO-^iniijr^aoaiO'— CNfO-^intor^QOoiO'-CNKi-* 



YEAR-OF-BIRTH 



csED UNKNOWN 



MALE 



FEMALE 



Figure 6.— Year-of-birth frequency distributions for red drum captured by purse seine from offshore northern Gulf of Mex- 

 ico waters, September 1985-October 1987. 



23 



