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Fishery Bulletin 117(3) 
Figure 4 
Two-phase growth model with 5 parameters that describes 
the growth of female (black diamonds, dotted line) and 
male (gray dots, solid line) Panamic stingrays (Urotrygon 
aspidura ) collected in the central zone of the Pacific coast 
of Colombia in 2006-2009 and 2015. Adjusted data for age 
and disc width were used, meaning that data take into 
account the months with peaks of reproduction. 
the growth parameters obtained from the TPGM-5 were 
considered best for describing the growth of this species. 
Similarly, TPGM was the best fitted to data for female 
blotched stingrays (Guzman-Castellanos, 2015) and to 
data for female thorny stingrays (Mejia-Falla et al., 2014), 
making it the most appropriate model in the 3 age studies 
carried out to date for the genus Urotrygon. 
The TPGM divides growth in 2 phases that could be 
related to changes in habitat, feeding habits, or the ener¬ 
getic investment of species (Aversa et al., 2011). The inflec¬ 
tion point of females in this model occurred at 2.3 years 
and coincided with the size at first maturity estimated 
for the Panamic stingray. This size at maturity occurred 
at 25 cm TL and corresponds to a DW between 13.8 and 
15.0 cm in our study (P. Mejia-Falla, unpubl. data). This 
change in growth rates (and their relationship with size at 
first maturity) has been associated with a higher energy 
investment in the development of reproductive organs, 
coinciding in some species with the change from juvenile 
to adult (Carlson and Baremore, 2005; Braccini et al., 
2007; Aversa et al., 2011). As a consequence, the trajectory 
in the growth rate allows us to distinguish between before 
and after maturity (Araya and Cubillos, 2006), with mat¬ 
uration starting before reproduction (Aversa et al., 2011) 
and possibly reflected in a lower investment of energy in 
growth (Mejia-Falla et al., 2014). 
Missing the smallest and largest individuals in a sam¬ 
ple can affect growth models and produce biased growth 
parameters (Haddon, 2001; Pilling et al., 2002; Smart 
et al., 2015; D’Alberto et al., 2017). The variables were sen¬ 
sitive to the low number of older age classes for both sexes 
and, for males, to the influence that the predominance of 
DW of 12-15 cm can have on data. This data sensitivity 
ensured that growth curves did not reach an asymptote 
resulting in underestimation of DW X (Fisher et al., 2013) 
and led to DW rx estimates of 24.71 cm for females and 
15.96 cm for males. The wide range in DW 0 could have 
been affected by a prolonged birthing period (Lessa et al., 
2006) in the TPGMs for both sexes. Additionally, the low 
number of samples for certain size and age classes in our 
study may have contributed to the variability in k. 
Among elasmobranchs, females reach greater asymp¬ 
totic sizes and have lower growth rates than males (e.g., 
Ismen, 2003; Skomal and Natanson, 2003; Ba§usta et al., 
2008; Kume et al., 2008). These differences in growth 
between sexes was observed for the Panamic stingray, with 
females reaching a of 24.71 cm and a k of 0.47 cm/ 
year and males reaching a DW m of 15.96 cm and a k of 
1.63 cm/year. Such differences between sexes have usually 
been attributed to males reaching maturity earlier than 
females. Females would have the evolutionary advantage 
of increasing their size to increase fecundity or to have the 
capacity of sheltering more embryos and reaching maxi¬ 
mum capacity (Aversa et al., 2011; Klimley, 2013). 
Differences in growth between sexes have been found 
in other species of the Urotrygonidae and Urolophidae, 
such as the thorny stingray, smalleyed round stingray, 
round stingray, lobed stingaree (Urolophus lobatus), 
sparsely-spotted stingaree (U. paucimaculatus), masked 
stingaree ( Trygonoptera personata), and western shovel- 
nose stingaree (T. mucosa ) (White et al., 2001; White et al., 
2002; White and Potter, 2005; Hale and Lowe, 2008; Mejia- 
Falla et al., 2014; Guzman-Castellanos, 2015; Santander- 
Neto 2015). Compared with those species, the Panamic 
stingray has a higher growth rate, the highest reported 
for an elasmobranch so far. This species provides more evi¬ 
dence for the fact that smaller organisms grow faster and 
have a shorter lifespan than larger organisms (White and 
Sommerville, 2010; Aversa et al., 2011). 
Although traditionally elasmobranchs have been 
described as K strategists, and they are therefore very vul¬ 
nerable to fisheries, the results of recent studies give evi¬ 
dence that this pattern is not a general one in this group 
and that some species have life history traits that make 
them more productive and resistant to fisheries (Simpfen- 
dorfer, 1993; Cailliet et al., 2005; Mejia-Falla et al., 2014; 
White et al., 2014). This pattern was found for the Pana¬ 
mic stingray, a small-sized species with a short life and 
fast growth, characteristics that are similar to those found 
in its sympatric species, the thorny stingray (Mejia-Falla 
et al., 2014). 
These life history characteristics have been advanta¬ 
geous for these species, allowing them to endure years of 
continuous fishing pressure (Rueda et al., 2006). There¬ 
fore, these characteristics make them 2 of the most abun¬ 
dant elasmobranch species in our study area, unlike 
other elasmobranchs, such as the Pacific smalltail shark 
(Carcharhinus cerdale), scalloped hammerhead ( Sphyrna 
lewini), scoophead (S. media), sicklefin smoothhound 
(Mustelus lunulatus), and longtail stingray ( Hypanus Ion- 
gus), among others (Navia and Mejia-Falla, 2016). Despite 
