Abstract. — Ages were estimated 

 for sheepshead Archosargus probato- 

 cephalus (Pisces:Sparidae) from Lou- 

 isiana waters using transverse sec- 

 tions of sagittae (otoliths). Opaque 

 annuli were validated to have formed 

 in sagittae once per year during 

 April and May in 1987 and 1988. Age 

 range was 1-20 years for fish mea- 

 suring 22-56 cm fork length and 

 weighing 0.4-3.6 kg. Von Berta- 

 lanffy growth models were different 

 for males and females; females ex- 

 hibited a faster growth rate and 

 achieved larger maximum sizes. 

 There was great variability in age at 

 a given length or weight, which pre- 

 cludes the use of morphometries as 

 age indices. Otolith weight provided 

 a more precise estimate of age than 

 fish length or weight. The considera- 

 tion of fish length or weight in addi- 

 tion to otolith weight significantly 

 improved the predictive capability of 

 multiple regression models. 



Age and Growth-Rate 

 Estimation of Sheepshead 

 Archosargus probatocephalus 

 in Louisiana Waters Using Otoliths 



Daniel W. Beckman 

 A. Louise Stanley 

 Jeffrey H. Render 

 Charles A. Wilson 



Coastal Fisheries Institute. Center for Wetland Resources 

 Louisiana State University. Baton Rouge, Louisiana J70803-7503 



W °ods Hole, Mass. 



LIBRARY 

 APR 1 W] 



Manuscript accepted 8 August 1990. 

 Fishery Bulletin, U.S. 89:1-8 (1991). 



The sheepshead Archosargus proba- 

 tocephalus is an estuarine/marine spa- 

 rid common in coastal waters of the 

 northern Gulf of Mexico. This species 

 supports significant commercial and 

 recreational fisheries off Louisiana. 

 Louisiana commercial landings of 

 sheepshead have increased substan- 

 tially in recent years, from 59 to 1111 

 metric tons between 1981 and 1989 

 (NMFS 1982, 1990), resulting in con- 

 cern for the species and consideration 

 of development of a management 

 plan. However, little has been re- 

 ported on sheepshead biology and 

 population dynamics. Of particular 

 concern is the lack of information on 

 age and growth. The only informa- 

 tion reported are average growth 

 rates for juveniles in North Carolina 

 (Hildebrand and Cable 1938) and 

 Florida (Springer and Woodburn 

 1960). The development of valid 

 management plans based on the cur- 

 rent available information would be 

 difficult. 



Otolith analyses have been proven 

 valid for age estimation of several 

 fish species occurring in the temper- 

 ate waters of the northern Gulf of 

 Mexico (Johnson et al. 1983, Barger 

 1985, Beckman et al. 1989, Beckman 

 et al. 1990a). Sectioning of otoliths is 

 often required in order to accurately 

 enumerate annuli for age estimation, 

 especially for long-lived species with 



large robust otoliths. Sample prep- 

 aration and ageing are often labor in- 

 tensive. As an alternative, Boehlert 

 (1985) suggested that otolith size may 

 provide objective, repeatable age es- 

 timates and save time and cost in 

 sample processing. Several studies 

 have documented otolith size as 

 greater for older fish than for young- 

 er fish of the same size (Templeman 

 and Squires 1956, Wilson and Dean 

 1983, Boehlert 1985, Reznick et al. 

 1989, Secor and Dean 1989), and sug- 

 gested that otolith weight be used to 

 estimate age. 



The purposes of this study were to 

 validate age estimates of sheepshead 

 in Louisiana waters using otolith (sa- 

 gitta) transverse sections, to derive 

 fish growth models, and to determine 

 the potential of using otolith weight 

 for age estimation of this species. 



Methods 



We sampled sheepshead (n = 784) 

 from February 1987 to August 1988. 

 Samples were taken by commercial 

 gillnet (15-18 cm [6-7 inch] stretch 

 mesh) (n = 461), trawl (n = 163), and 

 haul seine (n = 43); recreational hook- 

 and-line (n = 38) and spearfishing 

 (n = 27); and unknown gear types (n 

 = 52). Gillnet and haul seine samples 

 were predominantly from inshore 

 waters in the Mississippi Delta-Lake 



