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Fishery Bulletin 103(2) 



erford et al., 1989; Domier et al.. 1997), population 

 dynamics (Rutherford et al., 1989), juvenile food hab- 

 its (Hettler, 1989), juvenile distribution (Chester and 

 Thayer, 1990), and reproduction (Domeier et al., 1997; 

 Allman and Grimes, 2002). 



Few reports have been conducted on the age and 

 growth of gray snapper. Manooch and Matheson (1981) 

 used sectioned otoliths to age gray snappers from east- 

 ern Florida but did not validate their methods. Johnson 

 et al. (1994) also used sectioned otoliths to age fish 

 sampled from Fort Pierce, FL, to Grand Isle, LA, again 

 without validation of methods. Burton (2001) validated 

 the periodicity of opaque zone formation in gray snapper 

 from east coast Florida waters with the use of marginal 

 increment analysis of distal edge measurements. But 

 gray snapper have never been fully examined in the 

 northern GOM and comprehensive age, growth, and 

 mortality data from the thriving Louisiana recreational 

 fishery are virtually nonexistent. 



The objectives of our study were to describe the age, 

 growth, and mortality of gray snapper from the Loui- 

 siana recreational fishery. We obtained age information 

 through examination of cross-sectioned sagittal otoliths, 

 validated our aging techniques with the use of bomb- 

 radiocarbon 14 C and edge analyses, produced mortal- 

 ity estimates with standard procedures, and modeled 

 growth with the von Bertalanffy growth equation. 



Methods and materials 



Gray snapper were sampled from the Louisiana recre- 

 ational harvest from August 1998 to August 2002 by 

 personnel from the Louisiana State University Coastal 

 Fisheries Institute and the Louisiana Department of 

 Wildlife and Fisheries. Fish were opportunistically sam- 

 pled at charter boat facilities in Port Fourchon, LA, and 

 at spearfishing and hook and line fishing tournaments 

 in Grand Isle and New Orleans, LA. Morphometric 

 measurements (fork length [FL] and total length [TL] 

 in mm, total weight [TW] in g) were taken, sex was 

 determined by macroscopic examination of the gonads, 

 and both sagittae were removed, rinsed, and air dried, 

 weighed to the nearest 0.1 mg, and stored in coin enve- 

 lopes until processed. For specimens in which TL was 

 unavailable, TL was estimated from FL with the equa- 

 tion TL = 1.048(FL) + 8.35 (linear regression, df=275; 

 P<0.001; r 2 =0.98) calculated from specimens in which 

 both TL and FL were available. 



In order to estimate age of gray snapper, a transverse 

 section (~1 mm thick) was taken containing the core 

 of the left sagittal otolith of each specimen. Sections 

 were made with a Hillquest model 800, thin-sectioning 

 machine equipped with a diamond embedded wafering 

 blade and precision grinder (Cowan et al., 1995). In in- 

 stances where the left otolith was unavailable, the right 

 was substituted. Examinations of otolith cross-sections 

 were made under a dissecting microscope with trans- 

 mitted light and polarized light filter from 20x to 64x. 

 Opaque zones were enumerated along the ventral side 



of the sulcus acousticus from the core to the proximal 

 edge (Wilson and Nieland, 2001). Two readers (AJF 

 and MSB) performed opaque zone counts independently 

 without knowledge of capture date or morphometric 

 data. Otolith marginal edge condition was coded as 

 opaque or translucent by using the criteria described 

 by Beckman et al. (1989). Opaque zones were counted 

 a second time when initial counts differed. In instanc- 

 es where a consensus between readers could not be 

 reached, counts of the more experienced reader (AJF) 

 were used. Between-reader variation in opaque zone 

 counts was examined after the second readings of oto- 

 lith sections were completed. Differences in counts were 

 evaluated with the coefficient of variation (CV), index of 

 precision (D) (Chang, 1982), and average percent error 

 (APE) (Beamish and Fournier, 1981). 



Ages of gray snapper were estimated from opaque 

 annulus counts and capture date with the equation 

 described by Wilson and Nieland (2001): 



Day age = -182 + ( opaque increment count x 365 ) + 

 {(.m-l)x30)+d, 



where m = the ordinal number (1-12) of month of cap- 

 ture; and 

 d = the ordinal number (1-31) of the day of the 

 month of capture. 



The 182 days subtracted from each age estimate are to 

 account for the uniform hatching date of 1 July assigned 

 for all gray snapper to coincide with peak spawning 

 activity occurring in July (Domeier et al., 1997; Allman 

 and Grimes, 2002). Age in years was assigned by divid- 

 ing age (in days) by 365. Year of birth (YOB) was back 

 calculated by subtracting our otolith-based age esti- 

 mates from year of capture. 



Validation of the periodicity of opaque zone forma- 

 tion in gray snapper otoliths was examined with two 

 approaches. An advanced and accurate method of age 

 validation uses a quantitative measurement of nuclear 

 bomb-produced radiocarbon ( 14 C) that was accumulated 

 in carbon-containing hard parts of marine organisms 

 before, during, and after the atmospheric testing pe- 

 riod of nuclear weapons (1958-65) (Baker and Wilson, 

 2001). Elevated levels of 14 C have been observed in 

 hermatypic corals (Druffel, 1980, 1989) and this time- 

 specific marker can be used to validate age estimates 

 derived from hard parts in marine fishes (Kalish, 1993; 

 Campana and Jones, 1998). Baker and Wilson (2001) 

 recently validated red snapper otolith section age esti- 

 mates using this technique with excellent results. This 

 same method was applied in our study to the otolith 

 cores of gray snapper hatched after the nuclear testing 

 periods. 



Gray snapper hatched prior to 1973 were not avail- 

 able for our study, and thus the steepest portion of the 

 radiocarbon uptake curve could not be used to confirm 

 age estimates. Consequently, no coral reference data 

 for the general area were available after 1983. Because 

 red snapper otoliths have been previously validated 



