WALTZ ET AL.: BIOLOGY OF THE WHITEBONE PORGY 



Table 2.— Mean observed fork length, number and standard 

 deviation (SD) by age for otoliths, scales, and individuals given 

 identical ages by scales and otoliths of Calamus leucosteus. 



FL = -36.713 + 1.176 SR 



n = 757 r 2 = 0.82 



the best value of L x by using several trial values 

 of L x and regressing In (L x - L) against t, where 

 L = mean back-calculated fork length and t = age 

 (Ricker 1975). The straightness of this line is sen- 

 sitive to changes in L x and the L^ that pro- 

 duced the straightest line was L x = 331 for oto- 

 liths and L^ = 362 for scales. Values of K = 

 0.1731, to = -2.6390 for otolith ages and K = 

 0.2611, h = —0.3973 for scale ages were obtained. 

 The theoretical growth equations derived from 

 these values were 



Otoliths L, = 331 [l - e-0"31(t + 2.6390) j 



scales L, = 362 [l- e -o.26ii<t + o. 3 973)l 



Theoretical, back-calculated, and observed fork 

 lengths at age for scales and otoliths are com- 

 pared in Figure 4. 



where FL = fork length (mm), OR = otolith 

 radius (projector units), and SR = scale radius 

 (projector units). The intercepts of these predic- 

 tive equations were used as correction factors in 

 deriving average back-calculated fork length at 

 age (Table 3). Average back-calculated fork 

 lengths for fish aged with otoliths up to age XII 

 are 136, 179, 207, 227, 242, 252, 259, 264, 273, 280, 

 291, and 301 mm. For fish aged with scales up to 

 age IX average back-calculated fork lengths 

 were 102, 170, 215, 249, 275, 298, 303, 323, and 

 306 mm. Average observed fork lengths were 

 greater than average calculated lengths in all 

 cases for otolith and scale ages. Calculated 

 lengths for fish aged with otoliths show a closer 

 agreement with observed lengths than do cal- 

 culated lengths derived using scales. 



Mean back-calculated fork lengths (otolith 

 ages: I-XII; scale ages: I-VIII) were used to ob- 

 tain von Bertalanffy growth equations. Trial 

 values of L x = 304 for otoliths and L x = 349 for 

 scales appeared low. We were able to determine 



Table 3. — Back-calculated fork length at age for Calamus 

 leucosteus aged by scales and otoliths. 



350- 

 325- 

 300 

 27 5 

 250- 

 225- 

 200 

 I 75 

 I 50 

 E I25 



IOO- 



a 



z 



_l 



DC 



O 325 -| 



< 300 



275 

 250 

 225- 

 200- 

 175- 

 I 50 - 

 I 25 - 

 100- 



-a^* 



SCALES 



O- — O observed 



•— — • back calculated 



Q Q theoretical 



OTOLITHS 



II III IV 



~i r 



V VI 



AGE 



— 1 1 1 1 1 1 



VII VIM IX X XI XII 



Figure 4.— Observed, back-calculated, and theoretical fork 

 lengths of Calamus leucosteus aged by scales and otoliths. 



867 



