FABLE ET AL.: AGE AND GROWTH OF MACKEREL 



N =1.929 



JAN. FEB MAR. APR. MAY JUN. JUL. AUG. SEP. OCT. NOV. 



MONTHS 



[Numbers in parentheses are numbers of fish examined] 

 Figure 1. — Monthly percentage frequencies of Spanish mackerel otoliths with opaque margins. 



DEC. 



the same size interval. In the closely related king 

 mackerel, S. caualla, Johnson et al. (1983) re- 

 ported a similar situation. Our results substanti- 

 ate wide variation in growth rates of individual 

 Spanish mackerel. 



Growth 



Otolith radius (OR) was closely correlated with 

 fish length (FL). The curvilinear relation FL = 

 1.5091 ORi 2639 (^ = 0.944) had a slightly better 

 fit than the linear equation FL = -102.8061 + 

 6.1295 OR (r = 0.936). We used the former equa- 

 tion to back calculate lengths at former ages for 

 949 fish that had at least one annulus (838 fish 

 had no annuli and were classified as age 0). 

 Neither Klima nor Powell reported any equations 

 for an OR versus FL relationship. 



The mean back-calculated annual increments 

 of fork lengths for male and female Spanish 

 mackerel from all areas and years combined (Ta- 

 bles 4, 5) indicate that growth rates were rapid 



until age 5 in females and to age 6 in males (the 

 age 6 increment in males was based on one fish). 

 After these ages, growth rates slowed apprecia- 

 bly. Early growth was more rapid in females than 

 males (first annual increment 123.6 as compared 

 to 98.7). However, males maintained a higher 

 growth rate through age 6, except for age 5, when 

 the female annual increment was 55.3 mm versus 

 47.9 mm in males. 



Our back-calculations for Spanish mackerel 

 showed variation in mean fork lengths at age be- 

 tween sexes, areas, and years (Table 6). Females 

 from south Florida grew faster than any other 

 group and males from there grew faster than any 

 other males. For Spanish mackerel from north- 

 west Florida, where the largest number of fish 

 were collected, analysis of covariance (ANCOVA) 

 indicated significant differences in growth 

 (length-at-age) between sexes and collecting 

 gears (Table 7). 



ANCOVA was also used to test the significance 

 of growth differences among geographic areas 



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