McDonough and Wenner: Growth, recruitment, and abundance of luvenile Mugil cephalus 



351 



5(1(1 



400 



100 - 







A 



/; = 335 



r 1 1 1 1 1 1 1 1 1 



JAN FEB MAR APR MAY JUN JUL AUG SEP OCT 



250, g 



II = 2800 



20fl - 



E 

 E, 



x: 



oi 150 



c 



. \ 



„ \ 



o o 



1 1 1 1 1 1 1 1 1 1 



JAN FEB MAR APR MAY JUN JUL AUG SEP OCT 



Month 



Figure 9 



Mean age (A) and total length (B) at capture by month for young-of-the-year 

 striped mullet from the juvenile aging study, 1998 to 2000. 



growth curve (Fig. 10) for the rotenone study was described 

 by the equation 



Total length = 8.77 (month of capture)^" ±9.20 



(r2=0.950 and =235.0 at P=0.001 ). 



Month of capture was a good approximation of age because 

 January represented the approximate middle of the spawn- 

 ing season (October to April) and it provided a measurable 

 time frame in which to make both statistical comparisons 

 and calculate growth rates. 



The ANCOVA indicated that there was no significant dif- 

 ference between the slopes of our juvenile aging study and 

 the rotenone studies (P=0.001); the coefficients of varia- 

 tion were not significantly different, and the residuals were 



normally distributed. However, there was a difference in 

 the y-intercepts (0.346 for the juvenile aging study and 

 8.77 for the rotenone study). This difference was due to the 

 age factor used in the separate regressions. Days were the 

 units and in our juvenile aging study, whereas month of 

 capture was used for age in the rotenone study. The higher 

 r^ for size at age in the rotenone survey reflected the use 

 of changes in mean size per month for a larger sample 

 (?;=2576) than the actual size at age used for the juvenile 

 aging study data («=335). 



The distribution of back-calculated birth dates for 

 striped mullet from the juvenile aging study shows that the 

 main spawning period ranges from October through April 

 (Fig. IIA). The birthdate distribution for the rotenone fish 

 defines the main spawning period from October to Febru- 



