Baremore and Rosati: A validated, minimally deleterious method for aging sturgeon 
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Mississippi, and the U.S. Fish and Wildlife Service. 
Fork length (FL), total length (TL), and weight of each 
sturgeon were recorded in centimeters and kilograms, 
respectively, as part of these surveys. Collection of fin 
rays primarily occurred in the fall months, and sam- 
ples were collected on the Yellow, Choctawhatchee, and 
Apalachicola rivers from September 2010 through early 
November 2012. 
Validation of aging structure As part of the standardized 
sampling practices used for ongoing collaborative sur- 
veys, approximately 100 Gulf sturgeon received a dose 
of 10 mg of oxytetracycline (OTC) per kilogram of body 
weight, which was injected intramuscularly (Baremore 
and Rosati, 2011). An aging structure from each recap- 
tured, OTC-injected Gulf sturgeon was removed and 
sectioned according to the methods described previous- 
ly. These sections were then viewed under a dissecting 
microscope with reflected UV light to illuminate any 
potential chemical mark that the injected OTC had in- 
corporated within the structure. The placement of the 
chemical mark was evaluated in comparison with sub- 
sequently formed band pairs and with time at large to 
determine frequency of band formation. 
Results 
Sampling protocol 
Fin spines Removal of fin spines was considered to be 
invasive and possibly harmful to the fish because of 
bleeding, potential for the incised spine to snag in de- 
bris, and loss of hydrodynamics while swimming. The 
practicality of removal in the field was somewhat lim- 
ited, especially for Gulf sturgeon >120 cm FL, because 
a large hack saw was generally required. The band- 
ing pattern was consistent until about 15 band pairs 
were counted, a threshold after which band pairs often 
were compressed and reading bands became difficult 
(Fig. 2A). In many cases, the second marginal fin ray 
was incorporated in the spine, an occurrence that could 
obscure bands and make band counts less reliable. 
Because of their historic use and mostly clear band- 
ing patterns, fin spines were not excluded as an aging 
structure; however, they were considered not ideal for 
aging live sturgeon. 
Fin rays: dorsal, pelvic, and anal Removal of dorsal-, pel- 
vic-, and anal-fin rays from Gulf sturgeon was mini- 
mally invasive; these fin rays were small and not rigidly 
structured and could be removed easily. The required 
tools for removal were a scalpel, forceps, and wire cut- 
ters. Once sectioned, banding patterns were visible; 
however, bands were indistinct and inconsistent in rela- 
tion to the other structures (for image of dorsal-fin rays, 
see Fig. 2B). Although easy to remove and not harmful 
to the sturgeon, these fin rays were excluded as aging 
structures because of the lack of clarity of the bands. 
Otoliths Otolith removal was maximally invasive be- 
cause of their location in the head and could only be 
performed on mortalities. Otoliths were also very dif- 
ficult to retrieve because of the bony structure and 
size of Gulf sturgeon. Band pairs could be difficult to 
distinguish and were inconsistent among individuals; 
therefore, band counts could not be quantified for this 
structure (Fig. 2C). The use of otoliths for aging Gulf 
sturgeon was determined to be neither feasible nor ac- 
ceptable for a threatened species. 
Second marginal pectoral-fin ray The second marginal 
pectoral-fin ray was larger and more rigidly structured 
than the fin rays from other fins of Gulf sturgeon. Al- 
though removal of this fin ray was slightly more inva- 
sive because of its size, the effect of its removal on the 
sturgeon was considered to be negligible. The removal 
of this fin ray was relatively easy in the field and re- 
quired the same tools as the other fin rays. Further- 
more, band formation was mostly clear and consistent 
for the majority of samples (Fig. 2D). Therefore, on the 
basis of our established criteria, the second marginal 
pectoral-fin ray was chosen as the best structure for 
aging Gulf sturgeon. 
Removal of the second marginal fin ray was simple 
and could be completed by an experienced biologist in 
less than 1 min. The tools necessary for removal were 
small, inexpensive, and portable — notable differences in 
comparison with the hacksaw that was often required 
for the removal of fin spines. The second marginal fin 
rays of Gulf sturgeon >150 cm FL were more difficult 
to remove and often required a larger initial incision 
because of the diameter of the fin ray. The edges were 
often fractured from the force required to excise the 
sample, but the fin ray generally could be salvaged if 
the removed segment was at least 2 cm in length. 
Captured Gulf sturgeon were placed in a holding 
tank with their ventral surface facing up. A size 10 
scalpel was used to make a parallel cut on each side of 
the second marginal pectoral-fin ray approximately 2.5 
cm away from the point of articulation. This process 
acted to separate the second marginal fin ray from the 
spine and third marginal fin ray while allowing us to 
avoid major blood vessels. Wire cutters were then used 
to free the segment (1. 0-1.5 cm) by snipping each end 
of the parallel cut. The fin ray segment was removed 
with forceps, and a mixture of Betadine antiseptic so- 
lution (Purdue Products, Stamford, CT) and petroleum 
jelly was placed over the site for prophylactic purposes. 
Sampled fin rays were placed in labeled paper or plas- 
tic bags and allowed to air dry before processing. Sev- 
eral Gulf sturgeon that were sampled for age analysis 
were recaptured up to 6 months after the initial cap- 
ture to assess healing of the fin. 
Bleeding at the site of the incision was common but 
was generally minimal and stopped within 5 min of 
the cessation of the procedure. Recaptured individuals 
were healed completely 6 months after fin removal, and 
the fin showed less irritation at the removal site than 
