730 



Fishery Bulletin 98(4) 



Thompson'). These trends may reflect differences between 

 the modal length class (326-350 mm) of fish we sampled 

 from the eastern GOM and earlier collections (349-404 

 mm'" I from the Flower Garden Banks off Texas by Nelson 

 (1988). However, because we did not obtain specific depth 

 and gear information for fish we sampled, we cannot dis- 

 count these factors to explain differences between our sam- 

 ples and Nelson's 11988). Decreases in average and modal 

 lengths for red porgy in the SAB have been associated with 

 increased fishing pressure (Collins and Sedberry, 1991; 

 Harris and McGovern. 1997; Vaughan"'). 



Age, growth, and mortality 



Although scales and otoliths have been used to determine 

 the ages of red porgy, which structure is used, as well as 

 how it is prepared, affects ring interpretation. Although 

 we did not use scales to age red porgy, comparisons of 

 ring counts determined from scales and whole otoliths 

 from the same fish have had between SO'/r and 90'7f agree- 

 ment rates (Manooch and Huntsman, 1977; Machias et 

 al.. 1998). However, Manooch and Huntsman (1977) cau- 

 tioned that as age increases, both scales and whole oto- 

 liths become more difficult to interpret because the rings 

 at the outer edge become difficult to discern. We used sec- 

 tioned red porgy otoliths because most studies that have 

 compared aging structures have found that sectioned oto- 



liths provide more reliable estimates of age than either 

 scales or whole otoliths, particularly for older fish (e.g. 

 Beamish and McFarlane, 1983; Colhns et al., 1987; Low- 

 erre-Barbieri et al., 1994; Crabtree et al., 1996; Taylor et 

 al.^). Sectioning otoliths also increases readability rates; 

 Pajuelo and Lorenzo (1996) and our study were able to 

 assign ages to 81'7( and 97% of the otoliths, respectively. 

 Whole otoliths and scales used to age red porgy have pro- 

 vided mixed success in assigning ages to fish (54-90'7(: 

 Manooch and Huntsman, 1977; Nelson, 1988; Vassilopou- 

 lou and Papaconstantinou, 1992; Harris and McGovern, 

 1997; Machias etal., 1998). 



Opaque zones in red porgy otoliths appear to be formed 

 annually. From marginal-increment analyses, we found 

 that GOM red porgy form one opaque zone per year in 

 the late spring and summer Marginal-increment analy- 

 sis has also been Lised by others to validate annual zone 

 deposition in aging structures (Manooch and Huntsman, 

 1977; Nelson. 1988; Pajuelo and Lorenzo, 1996). Addition- 

 ally, Machias et al. (1998) reported that red porgy from 

 the Mediterranean Sea held in ponds for known periods 

 of time formed annual rings in both scales and otoliths, 

 and Collins et al. (1996) recaptured one oxytetracycline- 

 injocted red porgy (released in the SAB) in which the loca- 



* Reported lengths were transformed from FL to TL by using the 

 equation from Table 2. 



■' Taylor. R. G., J. A. Whittington. H. J. Grier, and R. E. Crabtree. 

 In prep. Age, growth, maturation, and protandric sex reversal 

 in the common snook, Ceittropomus undccimalis. from South 

 Florida waters. Florida Department of Environmental Protec- 

 tion, 100 Eigth Avenue SE. St. Petersburg, FL 33701-509.5. 



