172 
Fishery Bulletin 117(3) 
■ Female 
□ Male 
9 11 13 15 17 19 21 23 25 27 
Disc width (cm) 
012345678 
Number of band pairs 
Figure 1 
Frequency distribution of (A) sizes (disc width) and (B) ages (number of band pairs) for female and male 
Panamic stingrays (Urotrygon aspidura ) collected in the central zone of the Pacific coast of Colombia in 
2006-2009 and 2015 by small-scale, shallow-water shrimp fishing operations. 
i = the model; 
w i = the Akaike weight of model i; 
var (§i /; ) = the variance of the estimated parameter for 
model i; and 
0 = the estimated parameter for model i. 
Finally, differences in growth curves between sexes for the 
selected models were tested by using a likelihood ratio test 
(Kimura, 1980; Haddon, 2001). 
Results 
A total of 309 specimens of the Panamic stingray 
(184 males and 125 females) were analyzed, and only 
5 specimens were discarded for poor definition of band 
pairs and problems with reaching a consensus in read¬ 
ing. Female DW ranged from 7.1 to 26.5 cm, and male DW 
ranged from 7.0 to 18.5 cm, with most males measuring 
11-15 cm DW (Fig. 1A). Females were significantly larger 
(15.6 cm DW [standard deviation [SD] 5.5, n=124) than 
males (12.6 cm DW [SD 2.6], n=180, Z=3.92, PcO.OOOl). 
Readings of vertebral sections had high reproducibility, 
with no systematic bias between readers (P- 0.25; Fig. 2), 
high percentage of agreement between readers (87.4% 
with no differences in readings and 99.0% with differences 
of only 1 band pair), and relatively low error (APE=4.06%, 
CV=6.25%, n=309). Females had a maximum of 8 band 
pairs, but most of them (56.5%) had between 0 and 2 band 
pairs. Males had a maximum of 6 band pairs, and 91.7% 
of them had between 0 and 3 band pairs (Fig. IB). From 
seasonally adjusted data, the maximum ages were 7.5 and 
5.5 years for females and males, respectively. 
The analysis of edge type did not show a completely 
clear pattern with respect to the monthly deposition of 
band pairs. This result could have been influenced by the 
low number of specimens collected during the first quar¬ 
ter of the year (Suppl. Table 2) (online only). However, it 
was possible to observe a trend that indicates annual 
accumulation, with the opaque band forming from the 
first months of the year until July and the translucent 
band forming approximately from August until February 
(Fig. 3A). 
There were significant differences in MI among months 
(Kruskal-Wallis test: H= 24.06, P=0.008, n=141). Monthly 
variations of the MI indicate that band pairs start to form 
the opaque band during the first months of the year, with 
higher mean values in October and November when the 
translucent band is formed (Fig. 3B). Despite the small 
sample size during February-May, these results indicate 
an annual periodicity in the formation of band pairs. 
Age (mean count of Reader 1) 
Figure 2 
Age-bias plot of band-pair counts for Panamic stingrays 
(Urotrygon aspidura ) collected in the central zone of the 
Pacific coast of Colombia in 2006-2009 and 2015. The 
black dots correspond to the mean counts of Reader 2 rel¬ 
ative to those of Reader 1, and the bars indicate standard 
errors of the mean. The diagonal line indicates a one-to- 
one relationship. 
