NOTE Barger Age and growth of Pomatomus saltatn\ from U S South Atlantic and Gulf coasts 



807 



Results and discussion 



Agreement between investigators in enumeration of 

 marks was highest (92%) with whole otoliths. Lower 

 agreements were attained for scale impressions (67%), 

 vertebrae (33%), and scales (24%). In comparison of 

 whole otoliths with cross-sections taken from the other 

 otolith of a pair, investigators agreed 70% of the time. 

 The close spacing of marks in the sections caused more 

 disagreement in mark enumeration than did the wider 

 sjiacing in the rostrum of the whole otolith. Also, frac- 

 tures sometimes occurred in preparation of thin sec- 

 tions, making enumeration of marks on cross-sections 

 of otoliths a less viable option. In addition, 30 otoliths 

 were examined and no difference was found in mark 

 counts on either the rostrum or postrostrum of the 

 otolith or between pairs of otoliths. 



To use otoliths, or any structure, for age determina- 

 tion, the deposition of regular detectable age marks is 

 essential. Because samples were obtained from catches 

 of the fishery, no accepted method of direct validation 

 could be employed. However, indirect evidence was 

 established by correlation of the ol)served mark forma- 

 tion at the distal edge of the r'ostrum with month. 

 Despite the lack of samples for all months, the results 

 suggested that opaque marks were formed annually in 



late winter or early spring around March and April in 

 the Gulf and Atlantic samples, respectively (Fig. 2). 

 Gulf bluefish show an unexpected flattening of the 

 curve in June and July. The reason is not known, but 

 a likely hy]3othesis is a stress-induced check from en- 

 vironmental causes. An alternate hypothesis could be 

 a multiple spawning. However, there are no reports 

 of a summer spawn of bluefish in the Gulf. Backcalcula- 

 tion of length at the time of mark formation is depen- 

 dent on the relationship between the size of the age- 

 ing structure and fish length. Improved fit of the otolith 

 radii (OR) to length relationship occurred when natural 

 log transformation was used for fork length. The equa- 

 tion for Gulf bluefish was LOG(FL) = 4.200 + 0.389 x 

 OR (/•- = 0.86). The equation for Atlantic bluefish was 

 LOG(FL) = 4.822 -i- 0.248 x OR (r- = 0.61). 



Sexes were pooled for analysis because no significant 

 difference (a>0.10) was found between mean 

 backcalculated fork lengths of sex at age. Studies of 

 Hamer (1959) in the New York Bight, Lassiter (1962) 

 off North Carolina, and Richards (1976) off Long Island 

 also showed no appreciable difference in growth bet- 

 ween sexes. The length-weight equation for Gulf 

 bluefish was W = - 10.02 x FL-^" and was W = -9.18 

 X FL2 "?' for Atlantic bluefish. 



Backcalculated lengths-at-age from Gulf and Atlan- 

 tic bluefish were similar to the respective lengths at 



