NOTE Powell et a\ . Validation of age estimates from otoliths of Cynosaon nebulosus 



653 



ally clear juveniles. Our measurements from 23-d {n = V2) 

 and 32-d-old (n=15) juveniles averaged 52.4 )jm (SD=8.1). 

 Although our data were more variable, because we did not 

 select only clear otoliths, our measurement to the tenth 

 increment was similar to that of McMichael and Peters 

 (1989), indicating we were interpreting the central incre- 

 ments fairly accurately. 



Our relative lack of success in marking known-age larvae 

 could be due to an inadequate concentration of ALC (50 

 mg/L) or insufficient immersion time at that concentration. 

 Thomas et al. (1995) produced high mark quality on 6.0-9.0 

 mm red drum larvae at concentrations of 100 mg/L for as 

 little as 2-h immersions. Fish mortality was minimal (and 

 mark quality high) for immersion times up to 24 h at that 

 concentration. A concentration of 50 mg/L for 4 h appears to 

 be inadequate, however, for spotted seatrout larvae. Because 

 of the relative lack of success in marking small larvae at 50 

 mg/L, larger juveniles were immersed in a concentration of 

 100 mg /L and marking success was relatively high after 4-h 

 immersion, but still not 100%. Thomas et al. (1995) found 

 that mortality of larvae was fairly high 065%) at concen- 

 trations of 250 mg/L or higher: therefore longer immersion 

 times are probably necessary for 100% marking success. 

 Other investigators have had difficulties in marking larvae 

 with tetracycline immersion that were related to divalent 

 cations in full strength seawater (Campana and Nielson, 

 1982: Hettler. 1984: Gleason and Recksiek, 1990). 



In conclusion, we caution investigators that our inter- 

 pretation of increment counts for spotted seatrout may not 

 be valid for other studies. The skill of the otolith reader 

 is a critical component in otolith microstructure analysis 

 (Campana and Moksness, 1991): therefore, microstructure 

 analysis studies on spotted seatrout should require a sep- 

 arate validation study for each reader. 



Acknowledgments 



We are gi-ateful to Cameron Pratt for collecting wild- 

 caught fish, Patti Pickering for rearing and marking the 

 fish, and Curtis Lewis for photographing and preparing 

 the otolith figure. Dean Ahrenholz, Jon Hare, and two 

 anonymous reviewers reviewed the manuscript and pro- 

 vided many valuable comments. This research was sup- 

 ported by the NOAA Coastal Ocean Program. 



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