Wells et al.: Age validation of juvenile Isurus oxynnchus tagged off southern California 
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o Cailliet et al., 1983 
5 6 7 8 
Total band pairs 
10 11 12 13 
Figure 6 
Individual band-pair counts relative to size, shown in fork length (cm), of 
juvenile Shortfin Mako ( Isurus oxyrinchus ) from this study in= 29) com- 
pared with the average number of band-pair counts relative to size by 
Cailliet et al. (1983). Vertebral readings were similar between these 2 
studies, and only the assumption about deposition rates differed. Sharks 
for both studies were captured off southern California. 
et al. (2006) expanded on this study 
with 54 samples used for radiocarbon 
chronologies. Their results supported 
the hypothesis of annual band-pair 
deposition for older ages, but they did 
not rule out biannual band-pair depo- 
sition for young fish. Similarly, Natan- 
son et al. (2006) reiterated the afore- 
mentioned results and presented evi- 
dence of annual band-pair formation 
from an OTC-injected, 241-cm-FL, 
male Shortfin Mako at liberty for just 
over 1 year. However, growth curves 
generated from their tag-recapture 
and length-frequency data showed a 
much faster growth rate for young 
Shortfin Mako than the rate calcu- 
lated from vertebrae data, and the 
authors suggested the possibility that 
rates of band deposition may change 
with ontogeny. 
Bishop et al. 1 and Bishop et al. 
(2006) examined age and growth of 
Shortfin Mako from New Zealand wa- 
ters and assumed a deposition rate 
of 1 band pair per year on the basis 
of Campana et al. (2002) and Ribot- 
Carballal et al. (2005). They obtained 
a growth curve similar to that of Cail- 
liet et al. (1983), and their best-fit 
Schnute growth model predicted that 
growth was fast for the first few years 
of life (39 cm during year 1), then slowed for older ages 
to a rate that is similar to juvenile growth rates found 
in our study. Like Pratt and Casey (1983), they found 
that length-frequency data indicated considerably 
faster growth than did estimates from vertebral ages 
for the younger age classes with the assumption of 1 
band pair per year. Through the use of cohort analysis, 
Maia et a!. (2007) also reported fast growth in juve- 
nile Shortfin Mako collected from the longline fishery 
in the eastern North Atlantic (average growth rate of 
61.1 cm/year for the first year, and 40.6 cm/year for the 
second year). 
More recently, Okamura and Semba (2009) and 
Semba et al. (2009) examined monthly centrum edge 
patterns with a new statistical method and surface 
shadow technique to determine periodicity of band-pair 
formation. Their results indicated that the deposition 
of band pairs in Shortfin Mako in the western and cen- 
tral North Pacific has an annual cycle, but they also 
warned about sources of error from inaccuracies in cen- 
trum margin readings and from a large variability in 
the timing and duration of band deposition. 
Biannual band-pair deposition is not species-specific 
to Shortfin Mako; it reportedly has occurred in other 
shark species as well. Chen et al. (1990) and Anislado- 
Tolentino et al. (2008) suggested biannual band-pair 
deposition in the Scalloped Hammerhead ( Sphyrna 
lewini). In addition, Parker and Stott (1965) suggest- 
ed that 2 band pairs were laid down annually in the 
Basking Shark ( Cetorhinus maximus)', however, those 
conclusions were questioned by Pauly 4 (2002). Further, 
Natanson et al. (2008) examined vertebral growth pat- 
terns in C. maximus as a function of ontogeny and ques- 
tioned the feasibility of aging this species with vertebral 
band-pair counts. 
Ontogenetic differences may play a critical role in 
band-pair formation for Shortfin Mako, as well. Unfor- 
tunately, none of our OTC-marked vertebrae were from 
sharks >200 cm FL at tagging or recapture, but the 3 
largest sharks at recapture (172, 190, and 200 cm FL) 
exhibited a pattern consistent with biannual deposition. 
Two of these sharks (200 and 190 cm FL) were at liberty 
for more than 4 years and averaged 7.3 and 8.7 band 
pairs distal to the OTC mark, respectively, indicating 
that the biannual pattern continues in fish of this size. 
Both had similar total band-pair counts, averaging 9.3 
and 11.7, respectively. 
If one assumes a biannual pattern, as indicated by 
our OTC marking results, these fish would range from 
4 Pauly, D. 1978. A critique of some literature data on the 
growth, reproduction and mortality of the lamnid shark, Ce- 
torhinus maximus (Gunnerus). ICES Coucil Meeting Doc. 
1978/H: 17, 10 p. 
