Tagliafico et al.: Exploitation of Myliobcitis freminvillei off the coast of Venezuela 
147 
Table 2 
Mean catch per unit of effort (CPUE), measured as individuals per trip and as kilo- 
grams per trip and given with standard deviations in parentheses, for bullnose ray 
( Myliobatis freminvillei) captured in La Pared, Venezuela, during 2 periods: 2005-2007 
and 2013. 
Year 
Number 
of trips 
Number of 
individuals 
Catch (kg) 
CPUE 
(individuals/trip ) 
CPUE 
(kg/trip) 
2005 
10 
14 
27.8 
1.4 (1.8) 
2.8 (3.7) 
2006 
48 
33 
87.3 
0.7 (1.1) 
1.8 (3.0) 
2007 
69 
91 
306.6 
1.3 (1.4) 
4.4 (5.5) 
2013 
98 
49 
226.4 
0.5 (1.2) 
2.3 (6.4) 
All years 
225 
187 
648.1 
0.8 (1.3) 
2.9 (5.5) 
The highest monthly catch of 78.5 kg was registered 
in April 2013 (Fig. 2B). 
A clear trend for estimated CPUE, expressed as 
both the number of individuals caught per trip and ki- 
lograms caught per trip, was not observed during the 
study period (Fig. 2, C and D). Variance between years 
was homogeneous (Levene’s test: P>0.05). Statistical 
differences were observed in the number of individuals 
per trip and in the weight of the catches (kilograms 
per trip) between years but not between months (Ta- 
bles 3 and 4). The posteriori Tukey’s HSD test (P<0.05) 
revealed that both the average number of individu- 
als per trip and kilograms per trip were significantly 
higher in 2007 than in 2006 or 2013 (Table 2). During 
the study period, 59% of trips resulted in no catch of 
bullnose ray. 
Over the entire period of study, males occurred in 
slightly greater numbers than those of females, yet no 
significant difference was detected (% 2 (1, n=187): 1.37, 
P=0.242). In contrast, when considering each year inde- 
pendently, differences were found in 2005 (% 2 (1, n=14): 
5.79, P=0.016), 2006 (% 2 (1, n= 33): 4.36, P=0.037), and 
2013 (x 2 (1, n=49): 4.00, P=0.046>. 
Results from covariance analysis of the logistic re- 
gressions indicated that sex had no significant effect 
(P=0.673), and, as a consequence, an average value of 
DW50 was estimated for both sexes at 53.3 cm DW, in 
which 95% confidence intervals ranged from 52.6 to 
53.9 cm DW, whereas the slope of the regression was 
estimated at 0.42 with 95% confidence intervals from 
0.35 to 0.51. 
Immature females occurred less frequently (17%) 
than immature males (31%) in catches. Only 2 gravid 
specimens were reported during the entire study pe- 
riod: one in July 2007 (with 1 embryo of 9.0 cm DW) 
and the other in March 2013 (with 6 embryos: 2 fe- 
males and 4 males between 19.7 and 20.6 cm DW). 
In addition, a postgravid female was captured in July 
2007. Mature individuals were observed in almost all 
months for which landings were registered; however, 
a low number of gravid and postgravid females were 
recorded over the study period (Fig. 3). 
Discussion 
The maximum size of bullnose ray examined in this 
study (118.0 cm DW) exceeded the previous maximum 
size reported for this species in Venezuela (97.0 cm 
DW; Cervigon and Alcala, 1999), in Brazil (100.0 cm 
DW; Bernardes et al., 2005), and in Argentina (106.0 
cm DW; Refi, 1975). It is probable that the larger maxi- 
mum size observed is due to the long duration of our 
study and the greater number of individuals analyzed, 
in comparison with other studies of the bullnose ray. 
Schwartz (2011), for example, reported the occurrence 
of a greater maximum DW (males: 165.0 cm, females: 
147.0 cm) in Onslow Bay, North Carolina, over an ex- 
tremely long time period (1972-2010) using 2 different 
capture methods (braided nylon long lines and otter 
trawls). On the other hand, Stehmann (2009) reported 
that 70.0 cm DW was the most common size for this 
species; in contrast, the most common size interval re- 
corded in this study was between 55.0 and 60.0 cm DW. 
The average size of the bullnose ray observed (n=187) 
was 60.0 cm DW (SD 15.0 cm), similar to the mean 
size reported by Schmidt et al. (2012) for this species 
in Brazilian fisheries (63.8 cm DW [SD 7.0 cm], n= 8); 
however, the average weight calculated in our study 
(3.4 kg [SD 2.8]) was slightly lower than that reported 
for bullnose ray in Brazil (3.6 kg [SD 1.3]). 
Average DW of captured organisms increased from 
51.9 cm (SD 4.4) in 2005 to 69.4 cm (SD 13.3) in 2013. 
In addition, the average recorded weight of captured 
organisms increased from 2.0 kg (SD 0.5) in 2005 to 
5.1 (SD 2.8) in 2013 and weight increased steadily 
over the study period (average annual weights were 
2.0, 2.7, and 3.4 kg per individual for 2005, 2006, and 
2007, respectively). However, it is important to note 
that applied fishing effort was greater in 2013 than 
in previous years. Also, a total ban of the Venezuelan 
industrial trawling fishery occurred in 2008, a change 
that potentially may have increased food availability 
for bullnose ray, resulting in an increased size of bull- 
nose ray and in a redirection of fishing effort. Both of 
these factors could explain the observed increase in 
