Schmidt et al.: Spanish mackerel age, growth, and reproduction 



53! 



Females 



27 12 14 46 40 41 82 21 34 5 30 



100 



1 2 3 4 5 6 7 8 9 10 11 12 



MM = Developing 



Mi = Ripe 



fTTTTTI = Spent 



Males 1=3 = Resting 



5 8 60 61 31 20 48 30 39 20 18 



100 



Figure 4 



Percentage composition of reproductive states by month for 

 340 female and 352 male Spanish mackerel, Seomberomorus 

 maculatus, based on histological criteria. Number of speci- 

 mens examined is above the bar. 



Discussion 



While we lack direct evidence that growth rings on 

 otoliths are deposited annually, indirect evidence sup- 

 ports that hypothesis. Otolith radius and FL are pro- 

 portional as defined by the linear regression analysis, 

 and the mean observed and back-calculated lengths at 

 age agreed reasonably. In addition, the growth rings 

 on otoliths apparently formed during a 2 to 3 month 



period. The relatively high (29%) percentage of oto- 

 liths with opaque margins in November was likely an 

 artifact of the very small sample size ( 7 ) for that month. 



The period of annulus formation that we observed 

 agrees well with previous reports. Powell (1975) found 

 that annuli formed during May^July in "Florida" (i.e. 

 Gulf of Mexico and Atlantic) Spanish mackerel. Annu- 

 lus formation may be slightly earlier (March-May) in 

 fish from the northern Gulf of Mexico (Fable et al., 

 1987). 



We found two 11-year-old fish, extending the reported 

 longevity of Spanish mackerel slightly. Klima's (1959) 

 oldest fish were 6 years old, Powell's (1975) was 8 

 years old, and Fable et al. (1987) reported one 9-year- 

 old fish. Our mean back-calculated lengths at age 

 tended to be slightly smaller than those of Powell ( 1975) 

 after his standard lengths were converted to fork 

 lengths (using his equations), and our values for von 

 Bertalanffy asymptotic lengths (Lj were similar to his 

 (555mm for males, 694mm for females). In compari- 

 son to the back-calculated lengths (Atlantic and Gulf 

 of Mexico samples combined) of Fable et al. ( 1987), our 

 back-calculated lengths were greater at age 1 and 

 smaller at older ages. Their estimate of asymptotic 

 length for females was similar to ours, but their esti- 

 mate for males (794 mm) was much larger. Fable et al. 

 (1987) reported greater asymptotic lengths for males 

 than for females, while other studies found the re- 

 verse to be true (Powell, 1975; Helser and Malvestuto, 

 1987; present study). Powell (1975) excluded the old- 

 est fish from all analyses owing to small sample sizes 

 (19 fish age 6-8). Fable et al. (1987) used all age classes 

 regardless of sample size and concluded that the re- 

 sulting growth parameters were more realistic than 

 those reported by Powell (1975). Whether the differ- 

 ences in growth parameter estimates between this and 

 previous studies are due to methodological differences 

 (e.g., sectioned vs. whole otoliths) or to differences in 

 geographical coverage is not known. 



Examination of 547 female Spanish mackerel 

 <325 mm FL in the present study confirmed the lower 

 limit of size at maturity reported by Finucane and 

 Collins ( 1986), who based their estimate on nine speci- 

 mens <325mm FL from Georgia and the Carolinas 

 (Table 5). Our estimate of size at maturity for females 

 was higher than the estimate of Klima ( 1959). We found 

 that males matured at smaller sizes than reported by 

 Klima (1959) and Finucane and Collins (1986). These 

 differences probably reflect the greater accuracy re- 

 sulting from our histological versus their macroscopic 

 methods. 



Our age-at-maturity data generally concurred with 

 the qualitative data in previous studies showing that 

 female and male Spanish mackerel mature at ages 0- 

 1 (Table 5). Using a histological method, Powell ( 1975) 



