Natanson and Deacy: Changes in vertebral band-pair deposition rates with ontogeny in Carcharhinus p/umbeus 
51 
target species of the bottom longline fishery for coastal 
sharks since the 1980s (NMFS, 1993). In 2007, amend¬ 
ments to the Consolidated Atlantic Highly Migratory 
Species Fisheries Management Plan limited the take of 
the sandbar shark to a research fishery with the intent 
to collect life-history and catch data (NMFS, 2007). 
Since the implementation of this research fishery, col¬ 
lected vertebral samples have been used for age and 
growth analysis for the stock assessment of this species 
(SEDAR, 2011, 2017). 
Discrepancies exist among the previously published 
age and growth studies on sandbar sharks, largely be¬ 
cause of lack of validation of band-pair periodicity in 
the early vertebral studies (Casey et al., 1985; Casey 
and Natanson, 1992; Sminkey and Musick, 1995; An¬ 
drews et al., 2011; Hale and Baremore, 2013; Romine 
et al., 2013). Both growth curves generated in models 
from tag-recapture data and results from bomb radio¬ 
carbon analyses suggest slower growth and a longer 
lifespan than that estimated by using band-pair counts 
on vertebral centra (Casey and Natanson, 1992; An¬ 
drews et al., 2011). Additionally, results from the bomb 
radiocarbon technique indicate that band-pair counts 
approximated annual deposition only until 10-12 years 
of age (Andrews et al., 2011). 
We report on a long-term field study undertaken by 
the National Marine Fisheries Service’s Cooperative 
Shark Tagging Program to validate the band-pair peri¬ 
odicity of the sandbar shark in the western North At¬ 
lantic Ocean. Results from recaptured sandbar sharks 
that were tagged and injected with OTC between 1985 
and 2017 are presented and compared with results 
from previous studies. We also updated the tag-re- 
capture growth curve of sandbar sharks generated by 
Casey and Natanson (1992) to refine growth estimates. 
Materials and methods 
The Cooperative Shark Tagging Program tagged 39,405 
and recaptured 1603 sandbar sharks between 1962 and 
2017. Data recorded at tagging and recapture included 
size (fork length, total length, or weight), sex, location, 
and date; these data are referred to as tag-recapture 
data for the remainder of this paper. Sharks were 
tagged and recaptured by biologists, fisheries observ¬ 
ers, and commercial and recreational fishermen in the 
United States. Sharks tagged for age validation stud¬ 
ies were injected with a dose of OTC (25 mg per 1 kg 
of body weight), primarily by biologists on research 
vessels, and precisely measured before release. Only 
vertebrae from sharks with a reliably measured fork 
length (FL, from the tip of the snout to the fork in the 
tail, over the body) or total length (TL, from the tip 
of the snout to a point on the horizontal axis inter¬ 
secting a perpendicular line extending downward from 
the tip of the upper caudal lobe to form a right angle, 
over the body; Kohler et al., 1996) at both tagging and 
recapture were used in this study. We determined the 
reliability of measurement data on the basis of prior 
knowledge of the individual measuring the shark or de¬ 
tailed questioning of those individuals as to the method 
used. Measurements were converted to over-the-body 
FL, when necessary, by using the following equation 
(Kohler et al., 1996; n= 3734; coefficient of determina¬ 
tion [r 2 ]=0.9933): 
FL = 0.8175CTL) + 2.5676. (1) 
Processing of vertebrae 
For each shark, multiple vertebrae were removed from 
the area just posterior to the branchial chamber wher¬ 
ever possible; vertebrae were obtained closer to the 
head when sampling occurred onboard commercial ves¬ 
sels. We acknowledge that vertebral centra from dif¬ 
ferent parts of the vertebral column in carcharhinids 
have been shown to have varying band-pair counts 
associated with vertebral size (Natanson et al., 2018). 
Preliminary data show that, for sandbar sharks in the 
size range used in this study, band-pair count will be 
consistent along the vertebral column, allowing us to 
use vertebra from differing parts of the body (senior 
author, unpubl. data). All vertebrae processed for band- 
pair counts were stored frozen or in 70% ethyl alcohol 
in the dark until processing. Individual vertebrae were 
sectioned laterally through the focus by using gross 
sectioning (Natanson et al., 2006). 
Validation with oxytetracycline marking 
The accuracy of vertebral band-pair counts for use as 
annual indicators of growth was determined by using 
individuals that were recaptured after they were in¬ 
jected with OTC, tagged, and released. Between 1985 
and 2017, 7556 tagged sandbar sharks were injected 
with OTC, and data from 279 sharks (3.7%) were re¬ 
turned by 2017. Vertebrae obtained from 12 of these re¬ 
captured sandbar sharks were examined. Two pictures 
of each section, in the identical position, were taken 
by using 1) reflected white light for band-pair counts 
and 2) reflected long-wave UV light (366 nm) with the 
exposure increased to 20 s to obtain images of the OTC 
mark. Images were taken with a Nikon DSR12 1 digi¬ 
tal camera (Nikon Corp., Tokyo, Japan) attached to a 
Nikon SMZ1500 stereo microscope (Nikon Instruments, 
Inc., Melville, NY). Magnification varied with the size 
of the section, and a scale was included in each photo. 
Band pairs (consisting of one opaque and one trans¬ 
lucent band; Casey et al., 1985) were counted and 
marked independently by 2 experienced age readers 
using image editing software (Adobe Photoshop Ele¬ 
ments 6, Adobe, Inc., San Jose, CA). Each band pair 
was marked on an individual layer in Adobe Photoshop 
by the readers following Natanson et al. (2018), and 
each layer was considered a count. Once the readers 
1 Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
