Torres-Palacios et al: Age and growth parameters of Urotrygon aspidura 
173 
100 % 
90% 
80% 
70% 
§> 60% 
Co 
1 50% 
o 40% 
a. 
30% 
20% 
10 % 
0 % 
A c Translucent band growing ^ Opaque band growing 
Translucent band ending ■ Opaque band ending 
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 
Month 
Figure 3 
Monthly variation in the formation of vertebral band pairs of Pana- 
mic stingrays (Urotrygon aspidura) collected in the central zone of 
the Pacific coast of Colombia in 2006-2009 and 2015. (A) Percent¬ 
age ofPanamic stingrays (sample size [n]=237) that had 1 of 4 edge 
types: opaque band growing or ending and translucent band grow¬ 
ing or ending. Numerals inside column sections indicate the num¬ 
ber of vertebrae with that edge type. (B) Marginal increment index 
(n=141), with black dots corresponding to the median and the error 
bars indicating the 25th and 75th percentiles. Numerals above the 
top error bars indicate the sample size for each month. 
Growth estimation analyses were more conclusive when 
seasonally adjusted age data were used, with both the 4- 
and 5-parameter models (TPGM-4 and TPGM-5) for both 
sexes having the higher Akaike weight values (Tables 1 
and 2). Parameters estimated from multi-model inference 
based on those TPGMs for both sexes are provided at the 
end of Tables 1 and 2. 
The TPGM-5 was chosen for both sexes on the basis of 
statistical (AIC ; ) and biological (known maximum DW, DW 
at birth, and DW at maturity) fit (Tables 1 and 2, Fig. 4). 
The growth curves from the TPGM-5 were significantly 
different between sexes (likelihood ratio test: x 2 =115.6, 
df=5, jP< 0.0GQ1), although the inflection point was similar 
between sexes (likelihood ratio test: % 2 =1.024, 
df=l, P=0.312; Tables 1 and 2; Fig. 4). Female 
Panamic stingrays had a larger asymptotic DW 
(likelihood ratio test: % 2 =748.1, df=l, PcO.OOOl) 
and a lower growth coefficient (likelihood ratio 
test: % 2 =65.2, df=l, P<0.0001) than male Panamic 
stingrays. 
Discussion 
Despite the significant increase in the number 
of age and growth studies in batoids, only 3 of 
the 16 American round ray species of the Uro- 
trygonidae have been aged (Mejia-Falla et al., 
2014; Guzman-Castellanos, 2015; Santander- 
Neto, 2015). Our results agree with those of pre¬ 
vious studies and demonstrate that the Panamic 
stingray is a fast-growing and short-lived species. 
This finding has considerable implications for 
the population assessment and management of 
this species. 
The results from our study indicate that the 
vertebrae of Panamic stingrays, despite their 
small size, were adequate structures for evaluation 
and estimation of age for this species, with lower 
APE and CV values for readings than the averages 
of the age studies reported by Campana (2001) 
(APE<5.5% and CV<7.6%) and those observed in 
readings for species of the Urotrygonidae (average 
APE=4.24%; Mejia-Falla et al., 2014; Guzman- 
Castellanos, 2015; Santander-Neto, 2015). 
The region of the vertebral column chosen 
for extraction of the centra sample and the cen¬ 
tra size have effects on the counting of shark 
growth band pairs, with the largest ones show¬ 
ing more pairs of bands (Natanson et al., 2018). 
In this study, we used the largest centra of each 
specimen from the abdominal region, to main¬ 
tain homogeneity in samples and reduce those 
effects. This issue can be addressed by alter¬ 
native techniques, such as bomb radiocarbon 
dating or chemical fluorochrome marking, but 
these techniques are costly and are not easily 
accessible. 
Despite the limited sample size in the first 
months of the year, the results of MI analysis indicate 
that band-pair formation tends to be annual in Panamic 
stingrays, with constant MI growth from the beginning of 
the year until October and November. Although MI anal¬ 
ysis has been considered a validation method (Campana, 
2001), in this study, we used it as a method for verifica¬ 
tion of the periodicity in band deposition (Cailliet and 
Goldman, 2004). This annual band-pair deposition based 
on MI has been described for numerous species from 
the Urolophidae and Urotrygonidae (White et al., 2001; 
White et al., 2002; White and Potter, 2005; Mejia-Falla 
et al., 2014; Guzman-Castellanos, 2015; Santander-Neto, 
2015). Yearly periodicity of band-pair formation has been 
