Marquez-Farias: Length at maturity of the Squatina californica in the Gulf of California in Mexico 363 
Proportion mature 
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_ 
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= 
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1 
= 
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e) 
_ 
o 
Total length (cm) 
Figure 5 
The proportion of (A) female and (B) male Pacific angel 
sharks (Squatina californica) that were mature, by total 
length, among those captured from the eastern Gulf of Cal- 
ifornia in Mexico between 1998 and 2005. The dashed lines 
indicate the 95% confidence intervals of the estimated pro- 
portions from the logistic function. 
angelshark (S. aculeata) (Capapé et al., 2005), and angular 
angel shark (S. guggenheim) (Colonello et al., 2007). How- 
ever, at some point, the length structure of a stock can be 
altered by the level of historical exploitation (Stevens 
et al., 2000). Different factors, such as migration and gear 
selectivity, can influence the observed lengths in a sample. 
In particular, the effect of gear selectivity may be signifi- 
cant when interpreting life history characteristics and 
could distort growth curves and maturity ogives (Walker 
et al., 1998; Walker, 2005). 
The artisanal elasmobranch fishery in the GOC is 
intense and has been developing for several decades 
(Bizzarro et al., 2009). It is likely that the maximum sizes 
between sexes are similar in this study because Pacific 
angel sharks no longer reach the sizes they had reached 
before exploitation became extreme. The level of exploita- 
tion in the GOC does not allow individuals to reach maxi- 
mum size and affects the L5o. 
Walker (2005) suggested that reported differences in 
length at maturity may also be a result of the criteria 
adopted to define maturity. In early studies of the biology 
of sharks, length at first maturity was based mostly on the 
smallest mature individuals in the sample (Branstetter, 
1987). Such an approach fundamentally differs from the 
way L;, is estimated by using a binary logistic regres- 
sion (Walker, 2005, 2007). Technically, having insufficient 
data for the lengths of individuals that are in the transi- 
tion in maturity from immature to mature hampers max- 
imum likelihood estimation and makes estimation of the 
coefficients and 95% Cls of the logistic function challeng- 
ing (Christmann and Rousseeuw, 2001). The reproductive 
strategy of the Pacific angel shark, including vitellogenesis 
and the gestation period, can be understood only with sys- 
tematic monitoring over time (Castro, 2009). Such monitor- 
ing can be challenging because some shark species are not 
available in fishing grounds year-round. 
The incidental catch of Pacific angel sharks in artisanal 
and trawl fisheries in the GOC is concerning because of the 
low resilience of this species to fishing mortality (Cailliet 
et al., 1992). There are still gaps in our knowledge of the 
natural history of this species in the GOC; research needs 
include examination of seasonal migratory patterns and 
studies of age and growth. The estimate of L,;, from this 
study provides an important input to estimation of demo- 
graphic characteristics. The maturity ogive produced by 
using a logistic function suitably represents the develop- 
ment pattern of this species because it describes maturity 
as a gradual process. 
Acknowledgments 
The Lucile and Packard Foundation and Instituto Nacional 
de Pesca y Acuacultura partially supported data collec- 
tion. I thank L. Gonzaélez-Ania for review and advice on 
the results of the general linear model. I am grateful to 
C. Lozano-Albert and M. Weber for their language editing. 
The comments and suggestions of 2 anonymous reviewers 
are much appreciated. 
Literature cited 
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Bizzarro, J. J., W. D. Smith, J. F. Marquez-Farias, J. Tyminski, and 
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1987. Age, growth and reproductive biology of the silky shark, 
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1992. Growth and demography of the Pacific angel shark 
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