WARLEN; AGE AND GROWTH OF LARVAL GULF MENHADEN 



20 



15 



10 



20 



15- 



10- 



Louisiana 

 Dec 1981 



I 



1 

 1 1 1 



1 1 1512 21; 



21246212 " 

 2 1611 

 12 51 i^21 1 t 

 r4121 1 1 

 1212 ^\ 14 31 

 nil 222 



21 1 

 2 1 1 



Louisiana 

 Feb 1982 



_L 



Texas 

 Feb 1982 



J_ 



J- 



10 20 30 40 



ESTIMATED AGE (days) 



50 



60 



Florida 

 Feb 1982 



I 



10 20 30 40 50 



ESTIMATED AGE (days) 



60 



Figure 7. — Growth of larval gulf menhaden collected in 

 the winter 1981-82 in the northern Gulf of Mexico. The 

 Gompertz model was used to describe the data from all 

 transects except Texas December 1981 where it could 

 not be made to fit the data. Coincident data points are 

 labelled as in Figure 4. 



ida in both December 1980 (Fig. 6b) and in Febru- 

 ary 1982 (Fig. 7d), off Louisiana in February 1982 

 (Fig. 7c), and off Texas in February 1981 (Fig. 6d) 

 represent larvae from fewer cohorts. 



DISCUSSION 



Laboratory observations indicate that larval 

 gulf menhaden on the average form one growth 

 increment per day on their otoliths and that 

 counts of these increments can be used to esti- 

 mate age. Otoliths of larval gulf menhaden are 



thin and round, and the increments are generally 

 easily counted and consequently are ideally 

 suited for ageing. The most closely spaced incre- 

 ments, those occurring near the focus, were at 

 least 1.5 |xm wide and were above the 0.2 jxm 

 resolution of the light microscope (Campana and 

 Neilson 1985). First increment formation occurs 

 about 5 days after spawning and probably coin- 

 cides with first exogenous feeding. This is sup- 

 ported by Hettler ( 1984) who found that gulf men- 

 haden eggs hatched at about day 1.7 at 19°-20°C. 

 Four days after hatching larvae had functional 



85 



