147 
Abstract— The purpose of this study 
was to validate aging results of ju- 
venile Shortfin Mako ( Isurus oxy- 
rinchus) by vertebral band counts. 
Vertebrae of 29 juvenile Shortfin 
Mako marked with oxytetracycline 
(OTC) were obtained from tag-re- 
capture activities to determine cen- 
trum growth-band deposition. Tag- 
ging occurred off southern Califor- 
nia from 1996 to 2010, and time at 
liberty of the 29 sharks ranged from 
4 months to 4.4 years (mean=1.3 
years). Growth information also 
was obtained from length-frequency 
modal analyses (MULTIFAN and 
MIXDIST) by using a 29-year data 
set of commercial and research catch 
data, in addition to a tag-recapture 
growth model (e.g, the GROTAG 
model). For vertebrae samples used 
for age validation, shark size at time 
of release ranged from 79 to 142 cm 
fork length (FL) and from 98 to 200 
cm FL at recapture. Results from 
band counts of vertebrae distal to 
OTC marks indicate 2 band pairs 
(2 translucent and 2 opaque) are 
formed each year for Shortfin Mako 
of the size range examined. Length- 
frequency analyses identified 3 age- 
class modes. Growth rate estimates 
from 26.5 to 35.5 cm/year were cal- 
culated for the first age-class mode 
(85 cm FL) and from 22.4 to 28.6 
cm/year for the second age-class 
mode (130 cm FL). Results from the 
tag-recapture growth model revealed 
fast growth during time at liberty 
for tagged fish of the 2 youngest age 
classes. Collectively, these methods 
suggest rapid growth of juvenile 
Shortfin Mako in the southern Cali- 
fornia study area and indicate bian- 
nual deposition of growth bands in 
vertebrae for the first 5 years. 
Manuscript submitted 23 August 2012. 
Manuscript accepted 20 February 2013. 
Fish. Bull 111:147-160 (2013). 
doi 10.7755/FB.111.2.3 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessar- 
ily reflect the position of the National 
Marine Fisheries Service, NOAA. 
Age validation of juvenile Shortfin Mako 
Usurus oxyrinchus ) fagged and marked with 
oxytetracycline off southern California 
R. J. David Wells (contact author ) 1 - 2 
Susan E. Smith 1 
Suzanne Kohin 1 
Ellen Freund 1 
Natalie Spear 1 
Darlene A. Ramon 1 
Email address for contact author wellsr@tamug edu 
’ Fisheries Resources Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
8901 La Jolla Shores Drive 
La Jolla, California 92037 
Present address for contact author: Department of Marine Biology 
Texas A&M University at Galveston 
1001 Texas Clipper Rd 
Galveston, Texas 77553 
2 Department of Marine Biology 
Texas A&M University at Galveston 
1001 Texas Clipper Rd 
Galveston, Texas 77553 
For almost 3 decades, researchers in 
various parts of the world have fo- 
cused on the problem of accurately 
interpreting age and growth in the 
Shortfin Mako ( Isurus oxyrinchus) 
(e.g., Cailliet and Bedford, 1983; 
Cailliet et al., 1983; Pratt and Casey, 
1983; Casey and Kohler, 1992; Cam- 
pana et al., 2002; Bishop et al. 1 ; Ri- 
bot-Carballal et al., 2005; Bishop et 
al., 2006; Natanson et al., 2006; Ar- 
dizzone et al., 2006; Maia et al., 2007; 
Cerna and Licandeo, 2009; Okamura 
and Semba, 2009; Semba et al., 2009). 
Driving these efforts is the need to 
better assess the vulnerability of 
Shortfin Mako to harvest in commer- 
cial and recreational fisheries and as 
bycatch in longline and driftnet fish- 
eries from high-seas fleets (Stevens, 
2008). Studies of the demographic 
1 Bishop, S. D. H., M. P. Francis, and C. 
Duffy. 2004. Age, growth, maturity, 
longevity and natural mortality of the 
Shortfin Mako shark ( Isurus oxyrinchus ) 
in New Zealand waters. Working Paper 
SCTB17, BIO-4, National Institute of 
Water and Atmospheric Research, New 
Zealand, Ministry of Fisheries, NZ. 34 
p. Presented at the 17 th Meeting of the 
Standing Committee on Tuna and Bill- 
fish (SCTB), Majuro, Marshall Islands, 
9-18 August 2004. 
dynamics of sharks have shown that 
average age at first maturity and the 
relative rate of growth that deter- 
mines this parameter is one of the 
leading factors that affect the abil- 
ity of most sharks to rebound from 
harvest pressures (Smith et al., 1998; 
Cortes, 2002; Garcia et al., 2008). Ac- 
curate age determinations also are 
necessary for calculations of growth 
and mortality rates, age at recruit- 
ment, and longevity. 
The Shortfin Mako is an epipe- 
lagic species distributed in temper- 
ate and tropical seas worldwide 
(Compagno, 2001) and seldom found 
in water temperatures lower than 
13-17°C (Casey and Kohler, 1992; 
Stevens, 2008). Shortfin Mako occur 
off the U.S. West Coast principally off 
California and Oregon, and catches 
are associated primarily with warm 
sea-surface temperatures from 15° 
to 25°C (PFMC, 2011). Most Shortfin 
Mako off the U.S. West Coast are sex- 
ually immature, and high recapture 
rates for tagged juveniles show that 
young individuals remain for about 2 
years in nearshore California waters 
(Taylor and Bedford, 2001), where 
they are more frequently taken in 
the summer months and are only 
