Natanson and Deacy: Changes in vertebral band-pair deposition rates with ontogeny in Carcharhinus plumbeus 
53 
A 
\ 
5 mm 
Figure 1 
Images of sections of vertebral centra from 2 sandbar 
sharks (Carcharhinus plumbeus) injected with oxy- 
tetracycline (OTC) and tagged in the western North 
Atlantic Ocean in 1998 and 1996, respectively: (A) 
CM1031, which measured 156 cm in fork length (FL) at 
recapture in 2014, and (B) CM1027, which was 147 cm 
FL at recapture in 2006. The black line indicates the 
location of the OTC mark, and the black dots indicate 
the band pairs visible past the OTC mark. 
To directly compare validated age estimates at re¬ 
capture for OTC-injected sharks to the age estimates 
at size obtained from the tag-recapture models, age at 
tagging had to be assigned to each individual. Band- 
pair counts proximal to the OTC mark were used to 
assign age at tagging. Because counts of band pairs in 
sandbar sharks have been validated as annual up to 
10-12 years (Branstetter, 1987; Andrews et al., 2011), 
if the band-pair count proximal to the OTC mark was 
less than 12, an age at tagging could be assigned. Age 
at recapture then was estimated by adding time at lib¬ 
erty after tagging to count of band pairs proximal to 
the OTC mark. For example, a shark (CM1029) had 10 
band pairs before the OTC mark and was at liberty for 
9.5 years, resulting in age estimates of 10.0 years at 
tagging and 19.5 years at recapture. Then, estimates 
of age at recapture, along with the sizes at recapture, 
were compared with growth curves from the GROTAG 
model from this study and vertebral and tag-recapture 
models from previous studies (Casey et al., 1985; Casey 
and Natanson, 1992). Numbers of band pairs past the 
OTC mark were plotted against time at liberty along 
with a 1:1 line to determine whether band-pair counts 
were annual after the OTC mark. 
Results 
Validation with oxytetracydine marking 
Times at liberty for 12 recaptured sharks that were 
injected with OTC ranged from 0.1 to 16.1 years. Ver¬ 
tebrae from 10 of these specimens had a distinct OTC 
mark; 2 had no visible mark. Eight of these 10 re¬ 
captured sharks were at liberty for >1 year (3.8-16.1 
years) and were used for validation analyses (Table 
1). The remaining 2 specimens were at liberty for 0.1 
and 0.3 years (38-107 d), indicating that OTC was 
incorporated into the vertebra shortly after injection 
but growth distal to the mark was minimal. The size 
of specimens from which vertebrae were used ranged 
from 56 to 136 cm FL at tagging (Table 1). One shark 
(CM1031) was tagged as a young of the year; there¬ 
fore, it also was considered to have a known age at tag¬ 
ging (56 cm FL). Assigning a date of birth of 1 May to 
this sandbar shark (Baremore and Hale, 2012) meant 
it was ~4 months old at tagging, and adding those 4 
months to this shark’s 15.7 years at liberty resulted in 
an estimate of 16.1 years for its age at recapture. Data 
from another known young-of-the-year shark (CM751) 
indicate that OTC was incorporated within a month; 
therefore, the OTC mark in this animal was very close 
to the first clear band pair, possibly confirming Brans- 
tetter’s (1987) estimate that the first band pair is de¬ 
posited at 6 months of age (Fig. 1). 
Band-pair count past the OTC mark underestimated 
time at liberty from 23.5% to 58.0% in 6 of the 8 recap¬ 
tured sandbar sharks and validated annual deposition 
in the remaining 2 individuals at liberty for >1 year 
(Table 1, Fig. 2). Underestimation of age from the use 
of band-pair count past the OTC mark varied between 
1.3 and 9.1 years. Although data are limited, age un¬ 
derestimation from the use of band-pair counts does 
not appear related to sex because band-pair counts un¬ 
derestimated ages for individuals of both sexes. 
Sandbar sharks that were smaller at tagging (<100 
cm FL) showed less deviation between band-pair count 
and time at liberty. Annual band-pair deposition past 
