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Fishery Bulletin 111(2) 
4.5 to 6 years of age when collected. Examination of 
vertebral centra from some of our larger, non-OTC- 
tagged, recaptured Shortfin Mako reveals that as fish 
approach maturity, banding patterns appear to become 
more distinct, with both fast and slow growth zones 
becoming more regular and evenly spaced. Therefore, 
it is possible that these larger fish, on entering a more 
oceanic realm, change the periodicity of their band- 
ing pattern. On the basis of these results, it appears 
that Shortfin Mako <200 cm FL and found off Cali- 
fornia grow much faster than previously thought, with 
observed rapid growth (biannual band deposition) for 
approximately the first 6 years of life. Slower growth 
(annual deposition) thereafter may occur but cannot be 
confirmed by this study. 
Mechanisms that drive the observed biannual band- 
pair deposition may be linked to seasonal migration 
patterns and subsequent food availability. Through the 
use of similar OTC tag-recapture methods, Murphy 
et al. (1998) determined that Black Drum ( Pogonias 
crornis ) begin to deposit biannual band pairs after 4 
years of age because of a shift in migration patterns. 
Similarly, Shortfin Mako tagged in southern California 
appear to exhibit a biannual growth cycle, with fast- 
growth periods (wide, translucent band formation) in 
summer and winter and slow-growth periods (narrow, 
opaque band formation) in spring and fall. One possible 
explanation is that, as coastal waters warm and cool 
seasonally, juvenile Shortfin Mako move between rich 
feeding grounds off California in the summer and off 
Mexico in the winter and spend spring and fall migrat- 
ing between these feeding areas. 
Of the 15 OTC-marked sharks recaptured in Baja 
Mexico waters (Fig. IB), only 2 sharks were recaptured 
during summer months. In contrast, 70% of the returns 
of OTC-marked sharks in California coastal waters oc- 
curred during summer and there were no returns in 
the winter. In addition, on the basis of data from all 
tag recaptures (OTC and non-OTC-marked sharks, 
«=317, senior author, unpubl. data), 40% of all shark 
recaptures in Mexico (south of 30°N) occurred dur- 
ing winter, but only 7% of sharks were recaptured in 
Mexico during summer. Likewise, 58% and 7% of all 
recaptures in California coastal waters occurred during 
summer and winter seasons, respectively. Preliminary 
analysis of movements of juvenile (<150 cm FL) Short- 
fin Mako tracked with satellite tags (2003-10, n= 26) 
also shows high relative densities of Shortfin Mako at 
reported locations off Baja California, Mexico, in the 
winter and off California in the summer and more dis- 
persive offshore movements in the spring and fall (S. 
Kohin, unpubl. data). 
Tag-recapture techniques with OTC are among 
the most powerful methods for validation of age and 
growth patterns in fishes, but there are difficulties 
with this method. One disadvantage in the use of 
chemical marking and recaptures is that the number of 
band pairs formed for short times between tagging and 
recapture is often low, resulting in a potentially large 
relative error if one of the band pairs (such as on the 
growing edge) is misinterpreted (Campana, 2001). For 
example, misinterpretation of a single growth zone in a 
fish at liberty for 2 years would result in a 50% error, 
but the same misinterpretation in a fish at liberty for 10 
years would produce an error of only 10%. Fortunately, 
the relatively large sample size of 15 sharks at liberty 
for more than 1 year and 4 sharks at liberty for more 
than 3 years (2 of them for more than 4 years) allowed 
us to confirm the consistent banding patterns between 
both short- and long-term deployments. 
An additional problem with the use of chemical 
marking techniques, such as with OTC, is that growth 
may be inhibited (Pfizer, 5 1975; Monaghan, 1993); how- 
ever, other researchers that have worked with elasmo- 
branchs have shown OTC to have little adverse effects 
on growth (Tanaka [1990] for the Japanese Wobbegong 
[Orectolobus japonicus] and Gelsleichter et al. [1998] for 
the Nurse Shark [ Ginglymostoma cirratum]). Further, 
this problem does not appear relevant in this study be- 
cause fast (i.e., not inhibited) growth was observed with 
our OTC-marked juveniles. 
Conclusions 
Direct and indirect methods used in this study indi- 
cate rapid growth of juvenile Shortfin Mako in south- 
ern California and the OTC-marked vertebrae support 
a pattern of biannual deposition for the first 5 years 
of life. Accurate age and growth parameters in stock 
assessment models are important for fisheries man- 
agement and are necessary for calculations of growth 
and mortality rates, age at recruitment, and longevity. 
This article highlights the need to continue life history 
studies of elasmobranch species throughout different 
regions and ocean basins. 
Acknowledgments 
We thank personnel of the Southwest Fisheries Sci- 
ence Center for assistance in tagging and logistical 
operations to make this study possible: specifically, 
D. Holts, R. Rasmussen, R. Vetter, and J. Wraith. We 
also thank NOAA Fisheries observers for their diligent 
work in collecting specimens and length data and to 
the many anglers and commercial operators for return- 
ing OTC-marked vertebrae. We especially thank O. So- 
sa-Nishizaki for help with collection and shipment of 
samples from Mexico, G. Morse for sharing microscope 
and imaging equipment, and both A. Andrews and M. 
Francis for valuable suggestions and comments on ear- 
lier drafts. 
5 Pfizer, Inc. 1975. Oxytetracycline intramuscular solution 
leaflet 60-1051-00-8, 2 p. Pfizer Lab. Div., New York. 
