Abstract. — The periodicity of 

 increment formation and our abil- 

 ity to enumerate increments in sag- 

 ittal otoliths of Atlantic menhaden 

 are evaluated from hatching through 

 a nine-month period. We studied 

 otoliths from one group of field-col- 

 lected larvae that was marked by 

 immersion in oxytetracycline (OTC ) 

 and from a second group that was 

 marked by immersion in alizarin 

 complexone (ALC). Additionally, 

 otoliths from known-age juveniles 

 resulting from an Atlantic menha- 

 den laboratory spawning and rear- 

 ing experiment were examined. We 

 determined that, on the average, 

 larval and juvenile Atlantic men- 

 haden form one growth increment 

 per day. We were able to age juve- 

 nile menhaden reliably up to 200 

 days old within a confidence inter- 

 val (CI) of about 7 days and up to 

 250 days old within a CI of about 

 16 days. We hypothesized that 

 growth rates may have impacted the 

 periodicity of increment formation, 

 as well as our ability to count them 

 accurately. The statistically stron- 

 gest results were obtained from the 

 ALC-marked fish, which were reared 

 outdoors and displayed growth rates 

 (0.67 to 0.95 mm-day- 1 ) similar to 

 higher rates observed for juveniles 

 captured from estuarine nursery 

 areas. The periodicity of increment 

 counts for the ALC-marked fish 

 was less than one per day when 

 growth rates were observed to be 

 less than 0.3 mm-day -1 . Increments 

 in otoliths from the known-age and 

 OTC-marked fish, which were 

 reared indoors, had lower contrast 

 than their outdoor-reared counter- 

 parts. Otoliths were sectioned for 

 enumeration on both a transverse 

 and oblique-transverse plane. With 

 minor exception, no differences in 

 age estimation could be attributed 

 to the orientation of the sections. 



Confidence of otolith ageing 

 through the juvenile stage 

 for Atlantic menhaden, 

 Brevoortia tyrannus 



Dean W. Ahrenholz 



Beaufort Laboratory, Southeast Fisheries Science Center 



National Marine Fisheries Service. NOAA 



101 Pivers Island Road, Beaufort, NC 28516-9722 



Gary R. Fitzhugh 

 James A. Rice 

 Stephen W. Nixon 



Department of Zoology, North Carolina State University 

 RO. Box 7617, Raleigh, NC 27695-7617 



Wilson C. Pritchard 



Beaufort Laboratory, Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



101 Pivers Island Road, Beaufort, NC 28516-9722 



Manuscript accepted 21 September 1994. 

 Fishery Bulletin 93:209-216 ( 1995). 



The daily age information obtained 

 from larval and juvenile fish oto- 

 liths is a valuable tool for studies of 

 early life history and factors affect- 

 ing recruitment (Jones, 1992). Daily 

 age information is necessary for 

 backcalculating cohort-specific 

 spawning dates and is the best ap- 

 proach for estimating mortality and 

 growth rates in young fish (Essig 

 and Cole, 1986; Pepin, 1989; Jones, 

 1992). A prerequisite, however, is 

 the validation of the temporal peri- 

 odicity of otolith increment forma- 

 tion (Geffen, 1992). While the 

 otolith approach to determination of 

 vital rates has successfully been 

 applied to larval fish, use of otoliths 

 for the juvenile stage has been more 

 controversial, often because of ad- 

 ditional requirements of otolith 

 preparation, including sectioning 

 and polishing of otoliths, and be- 

 cause of increased uncertainty in 

 age estimations and back-calcula- 

 tions of size at age (cf. Rice, 1987; 

 Mosegaard, 1990; Jones, 1992). 



Many validation studies have de- 

 termined that increments are, on 

 average, daily in periodicity (cf. 

 Jones, 1986), but conditions affect- 

 ing a low growth rate, for example, 

 can result in increment periodicity 

 other than a daily one (Geffen, 

 1992) or can result in difficulty in 

 the detection of daily increments 

 (Campana, 1992). Therefore ageing 

 error commonly increases with age 

 and otolith size as increment widths 

 decrease with decreasing growth 

 rates, resulting in greater uncer- 

 tainty of ages, growth rates, and 

 birthdates (Rice et al., 1985; Rice, 

 1987; Campana and Jones, 1992). 

 We examined conditions where con- 

 fidence about the assumption of 

 daily ring deposition may be low 

 and what the consequence would be 

 of increased ageing error on age es- 

 timation for Atlantic menhaden, 

 Brevoortia tyrannus. 



Larger, older otoliths are more 

 difficult to prepare and read. To 

 address this issue, we also exam- 



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