FISHERY BULLETIN: VOL. 87, NO. 1 



across the coastline of the north-central Gulf of 

 Mexico. 



Validation 



Periodicity of formation of ageing structures must 

 be confirmed over all year classes to validate the use 

 of that hardpart for ageing (Beamish and McFarlane 

 1983). Beckman et al. (in press) validated that the 

 first two annuli were formed yearly in sagittae of 

 immature red drum from estuarine waters. The use 

 of marginal increment analysis in this study valid- 

 ated that annuli continued to be deposited in red 

 drum sagittae once per year in fish up to 37 years 

 old. There was no significant variability in timing 

 of annulus formation with stage of maturity or with 

 change in growth rates with age. 



Precise, reproducible age estimates were obtained 

 for red drum using transverse sections of sagittae. 

 Almost 100% agreement between two readers was 

 achieved by recounting otoliths or counting the fish's 

 other sagitta when age estimates disagreed. Initial 

 disagreements were usually resolved by recounting 

 the otolith, suggesting initial miscounts or errors 

 were due to recording and transcription. Unread- 

 able otoliths were primarily those with inadequate 

 sample preparation. Discarding difficult-to-age oto- 

 liths, which are often from older fish, could bias age 

 distributions as well as von Bertalanffy growth 

 parameters (Hirschhorn 1974). Recounting otoliths 

 for which age estimates did not initially agree and 

 utilizing both sagittae to obtain a readable sample 

 allowed us to minimize the number of unused 

 sections. 



The same seasonal pattern of annulus formation 

 reported in this study was observed in sagittae of 

 red drum in inshore estuaries (Beckman et al. in 

 press). This pattern is also similar to that observed 

 in another sciaenid, the Atlantic croaker (Barger 

 1985). The formation of an opaque zone in red drum 

 sagittae in winter and spring months may corre- 

 spond to reduced growth rate during this period 

 (Doerzbacher et al. 1988). In West African sciaenids 

 an opaque zone was formed apparently in response 

 to cold temperatures (Poinsard and Troadec 1966). 



Growth 



The von Bertalanffy growrth coefficients for other 

 sciaenids (e.g., Barger 1985; Wakeman and Ramsey 

 1985, cited by Pauly 1980) were generally greater 

 than those obtained for red drum in this study. 

 Growth parameters reported herein differ from 

 those obtained by Wakeman and Ramsey (1985) for 



red drum; however, their model was based only on 

 young fish from inshore waters that have higher 

 growth rates (Beckman et al. in press). The growth 

 models reported in this study were derived primar- 

 ily from mature slower growing fish. The negative 

 values of t^ predicted suggests that our models do 

 not adequately describe growth of young fish un- 

 represented in our data. Separate models may be 

 necessary to describe growth of immature red drum 

 from inshore waters (Richard Condrey pers. com- 

 mun.''). The large variation in size at age beyond 

 year 5 makes it impossible to precisely predict age 

 of red drum using length or weight. 



Our estimates of maximum red drum age are 

 greater than those previously suggested. Pearson 

 (1929), Simmons and Breuer (1962), and Wakeman 

 and Ramsey (1985) used the scale method and re- 

 ported a maximum age of 5, 3, and 4 years, respec- 

 tively. The use of validated ageing techniques for 

 red drum from otoliths more accurately estimates 

 their ages and provides much improved manage- 

 ment data bases. 



Female red drum attained significantly larger 

 sizes than did males, with growth curves diverging 

 with increasing age and maturity. Larger size in 

 females has been postulated as a life history strategy 

 in fish for increasing reproductive potential through 

 increased egg production capability (Roff 1983). The 

 similarities in age-class compositions between sexes 

 indicated that the increased female size was attained 

 through somewhat higher growth rates and not 

 greater longevity. 



Age Structure 



Examination of the age composition of the off- 

 shore population revealed that red drum begin to 

 appear in the offshore population as early as year 

 2. Their appearance offshore coincides with their 

 absence inshore by four or five years of age (Pear- 

 son 1929; Simmons and Breuer 1962; Wakeman and 

 Ramsey 1985). The 1973 year class was the most 

 abundant, and earlier year classes demonstrated a 

 decay pattern indicative of natural mortality. The 

 year classes since 1973 were variable and could be 

 interpreted variously to indicate several poor year 

 classes, high mortality, or incomplete recruitment 

 to offshore schooling populations, assuming no bias 

 in the sampling procedures. Inadequate data are 

 available to determine which are primary factors af- 

 fecting age distributions. 



'Richard Condry, Coastal Fisheries Institute. Louisiana State 

 University, Baton Rouge, LA 70803, pers. commun. January 1988. 



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