Baremore and Rosati: A validated, minimally deleterious method for aging sturgeon 
281 
ate the use of this fin ray as an aging structure. We 
found that the second marginal fin ray was simple to 
remove and that sections provided reliable and clear 
band counts. 
Otoliths and fin spines are commonly used to age 
fishes — fin spines being the most prevalent for stur- 
geon species (Huff 4 ; Brennan and Cailliet, 1991; Ros- 
siter et al., 1995; Stevenson and Secor, 1999; Everett 
et al., 2003). Although otoliths often are considered the 
best structure for aging fish (Casselman, 1987; Cam- 
pana, 2001), band formation in otoliths of Gulf stur- 
geon was unreliable and difficult to interpret. Similar 
difficulties have been noted for other sturgeon species 
(Brennan and Cailliet, 1989); however, bomb radiocar- 
bon dating has been used to validate band formation 
for 46 otoliths of lake sturgeon (Bruch et al., 2009). Fin 
spines provide mostly clear and interpretable banding 
patterns, and their use has been validated for sever- 
al species (Rien and Beamesderfer, 1994; Rossiter et 
al., 1995), but their removal has been discouraged for 
threatened and endangered sturgeon species because 
of the possibility of deleterious effects (Kahn and Mo- 
head, 2010). 
Although our precision and PA estimates were very 
high for band counts between the fin spine and second 
marginal fin ray, our age assignments could have been 
somewhat biased by the methods used. Because the fin 
spine and second marginal fin ray were often on the 
same slide, band counts were made in conjunction with 
both structures, rather than independent of each struc- 
ture. Future comparative studies should randomize the 
order in which fin rays and spines are read. 
Of the Gulf sturgeon that previously had been in- 
jected with OTC, 12 were recaptured and sampled over 
the course of this study. However, formation of annual 
bands in the second marginal fin ray was validated for 
only 3 of those Gulf sturgeon. Ages could not be vali- 
dated for the other recaptured Gulf sturgeons because 
OTC injections failed to produce a chemical mark in 8 
of those fish. This low rate of OTC incorporation may 
have been due to the methods used: Rien and Beames- 
derfer (1994) reported a 98% detection rate of OTC 
chemical marks in the fin spines of white sturgeon 
when they used a concentration of 25 mg/kg and Ros- 
siter et al. (1995) used a dose of 35 mg/kg to validate 
band formation in lake sturgeon . The use of a dose 
of 10 mg/kg in our study likely led to the high failure 
rate, and future validation studies for sturgeon species 
should use at least 25 mg/kg. Loss of OTC at the injec- 
tion site was also noted; therefore, a slow injection fol- 
lowed by pressure applied to the site is recommended 
as well. Despite the low detection rate, we feel confi- 
4 Huff, J. A. 1975. Life history of Gulf of Mexico sturgeon, 
Acipenser oxyrhynchus desotoi, in the Suwannee River, Flori- 
da. Florida Marine Research Publications 16, 32 p. Marine 
Research Laboratory, Florida Department of Natural Re- 
sources, St. Petersburg, FL. [Available from http://f50006a. 
eos-intl.net/ELIBSQL12_F50006A_Documents/FMRP016ocr. 
pdf.] 
dent that band pairs in the second marginal fin rays 
are annual marks. 
Although the set of methods used in this study was 
developed for Gulf sturgeon, it likely is widely appli- 
cable to other sturgeon species worldwide. Researchers 
have advised that caution be taken when the fin spine 
is used to age sturgeon because of difficulty with iden- 
tification of growth bands (Hurley et al., 2004; Jackson 
et al., 2007) and because of the potentially harmful ef- 
fects of removing the fin spine from large individuals 
(Kahn and Morehead, 2010). Additionally, the use of 
the second marginal fin ray may also be appropriate 
for species related to sturgeon, such as paddlefish. Ac- 
curate life history information is crucial for the devel- 
opment of population assessments and recovery plans 
but can be difficult to obtain for threatened and en- 
dangered species. The simple, field-ready methods de- 
scribed in this article can easily be adapted or modi- 
fied to suit ongoing monitoring programs of sturgeon 
and can be used to improve population assessments for 
these data-limited species. 
Conclusions 
The second marginal pectoral-fin ray provided an excel- 
lent alternative to fin spines for aging Gulf sturgeon. 
Removal was minimally deleterious, and the banding 
pattern was generally clear and consistent. Annual 
band formation was validated for 3 Gulf sturgeon with 
6, 7, and 8 band pairs, but 10 mg/kg is too low a dose of 
OTC to reliably mark calcified structures of Gulf stur- 
geon. A dose of 25 mg/kg is recommended for future 
validation studies. The methods described in this ar- 
ticle have wide applicability to other sturgeon species 
and are important for population assessment of these 
overexploited fishes. 
Acknowledgments 
Many researchers contributed expertise and samples, 
but we would especially like to thank D. Fox, K. Flem- 
ing, N. Willett, and F. Parauka for providing samples 
and field time. K. Sulak donated an archive of spines 
and fin rays, and M. Peterson, J. Havrylkoff, and T. 
Slack provided samples as well. C. Fioramonti, R. All- 
man, and C. Palmer lent advice and laboratory equip- 
ment, for which we are very grateful. We also thank S. 
Bolden and G. Davenport for giving us the opportunity 
to work with this species. 
Literature cited 
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2009. Using trace elements in pectoral fin rays to as- 
sess life history movements in sturgeon: estimating age 
