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Fishery Bulletin 111(2) 
10-110 kV at 3 mA and penetrates the highly calci- 
fied vertebrae. 
Samples were stored frozen until processed and kept 
from light and excessive UV exposure to preserve the 
OTC time mark. Whole centra were separated, cleaned 
of excess tissue, rinsed and air-dried. Once dry, 2 centra 
from each sample were chosen, and 2 types of sections 
were prepared with a low-speed circular saw (IsoMet, 
Buehler, Lake Bluff, IL). To duplicate the Cailliet et al. 
(1983) method of X-raying the whole centrum face and 
to avoid the double image of the anterior and poste- 
rior face superimposed in X-ray images, a transverse 
cut was made through the centrum to create 2 equal 
halves of the centrum face. Additionally, longitudinal 
(sagittal) sections, 0. 3-1.0 mm thick, were taken from 
the center of the second vertebrae to further elucidate 
banding patterns, especially growth zones along the 
centrum edge that are sometimes difficult to read on 
centrum face X-rays (Cailliet et al., 1983). Sections 
were then mounted and examined under a dissecting 
microscope at 7. 5-10. Ox magnification, with reflected 
long-wave UV light (365 nm) to illuminate the OTC 
mark. A metal pin was glued into place to visualize the 
position of the brightest, most distal edge of the OTC 
mark before it was X-rayed. Samples were X-rayed 
with a General Electric (Fairfield, CT) Mobile 100-15 
X-ray unit for exposures between 15 and 45 s at 5 mA 
and 20—40 kV by using Kodak Industrex M100 film 
(Readypack II; Eastman Kodak Co., Rochester, NY). X- 
radiographs were photographed with a Leica Z16 APO 
dissecting microscope with substage illumination and 
a Leica DFC420 digital camera (Leica Microsystems, 
Wetzlar, Germany). 
Standardization of band-reading techniques and terminology 
We examined data collected by commercial drift gill- 
net observers and from research longline surveys and 
determined the peak in abundance of postpartum-size 
Shortfin Mako <70 cm FL to identify peak parturition 
time off southern California. Most individuals (90%) 
were collected between August and November, provid- 
ing a tentative parturition time in our study region. 
Size at birth has been estimated at approximately 63 
cm FL (70 cm TL), with parturition occurring year- 
round according to Mollet et al. (2000); parturition may 
occur primarily in summer in the South Pacific (Duffy 
and Francis, 2001) and eastern North Atlantic (Maia 
et al., 2007). The birth band for counting purposes was 
identified as the most pronounced calcified first band 
distal to the centrum focus and indicated by a change 
in the angle of the centra (Bishop et al., 2006). Seasons 
were defined according to solstice and equinox periods 
in the Northern Hemisphere. 
Band-pair counts 
Band pairs were counted from digital images of X-ray 
photographs on a computer screen. We referred to the 
original X-rays if more detail was desired. As in Bishop 
et al. 1 and Bishop et al. (2006), counts excluded the 
birth band, which represents age 0. Alternating pairs of 
translucent bands (hypomineralized; appearing dark in 
X-ray) and opaque bands (hypermineralized; appearing 
light in X-ray) were assumed to represent one complete 
band pair. Two separate band counts were made: 1) to- 
tal band pairs, or bands distal to the presumed birth 
band, and 2) band pairs distal to the OTC mark. Band- 
pair counting began for the former at the distal edge 
of the first translucent zone beyond the birth band and 
for the latter at the distal edge of the first translucent 
zone beyond the OTC mark. In many cases, the OTC 
mark was directly on a translucent zone, but this zone 
was not included in the distal-to-OTC counts because 
only partial growth occurred during this period. This 
method results in counts that are conservative; counts 
are lower than they would be if this zone were includ- 
ed. If a count ended with a partial band pair (observed 
when the centrum edge was opaque), a plus sign was 
appended to the count number. For statistical analy- 
ses, the plus sign was converted to an arbitrary par- 
tial band count of 0.5. The corpus calcareum (centrum 
“arm”) was used as a primary counting surface, and 
bands in the intermedialia were used for confirmation 
of a band pair, although we were not always successful 
in acquisition of sections with the fragile intermedialia 
intact (Goldman, 2005; Branstetter and Musick, 1994). 
Each sample was examined and counted indepen- 
dently by 3 readers. Bands were “blind “counted with- 
out knowledge of Shortfin Mako length, sex, or time 
at liberty. Readers consulted with each other on cri- 
teria for counts before readings. Samples for which 
there was disagreement were counted a second time 
with X-ray images from which corresponding sample 
numbers had been removed and placed in a random 
order. Counts with similar readings among readers 
were deemed final; however, several samples did not 
have similar counts. For those samples without similar 
counts, the average number of band pairs was reported 
because differences were minor and no readings were 
deemed irreconcilable. 
Differences among final readings of each of the 3 in- 
dependent readers were examined through an analysis 
of variance (ANOVA) with readers as the dependent 
variable. A least-squares linear regression analysis 
was performed, and the null hypothesis that the slope 
( b ) of the relationship between the number of band 
pairs and time was 1:1 (a situation that occurred if 
one opaque and one translucent band were deposited 
each year) was tested with a two-tailed f-test (Kusher 
et al., 1992). Age bias was investigated with age-bias 
plots and chi-square tests of symmetry by using the 
contingency table methods of Bowker (1948) and Hoe- 
nig et al. (1995). Differences in band-pair counts among 
readers were evaluated by the average percent error 
(APE) (Beamish and Fournier, 1981) and coefficient of 
variation (CV) (Chang, 1982) for readings distal to both 
the OTC mark and birth band. 
