Tagliafico et at: Exploitation of Mytiobatis freminvillei off the coast of Venezuela 
145 
bullnose ray is commercially valuable and is consumed 
fresh or salted (Cervigon et al., 1992; Cervigon and Al- 
cala, 1999). Between 2006 and 2007, 13,000 kg of bull- 
nose ray were landed in the state of Nueva Esparta 
in Venezuela, representing 0.03% of the total landings 
from 176 commercially fished species (Marval and Cer- 
vigon, 2009). Although no fishery specifically targets 
this species, it is often landed as bycatch. 
The results of this study provide insight on the life 
history and landings data of the bullnose ray captured 
as part of a small-scale, artisanal fishery in Margarita 
Island — baseline information that would be useful for 
management and conservation of this little known and 
potentially vulnerable species. 
Materials and methods 
La Pared is a small and isolated fishing community lo- 
cated on the northern coast of Macanao Peninsula, Mar- 
garita Island, in the state of Nueva Esparta in north- 
eastern Venezuela (11°03'32.53"N, 64°18'47.25"W). At 
this place, fishermen manage the resources, rotating 
target species and using different gears depending 
on the time and abundance of fish (Tagliafico et al., 
2013a). 
All bullnose ray used in analysis for this study were 
sampled from fish landed with bottom gillnets at a site 
in this community. Descriptions of the boats and fish- 
ing gear of this fishery can be found in Mendez-Arocha 
(1963), Gines et al. (1972), Iriarte (1997), Suarez and 
Bethencourt (2002), and Gonzalez et al. (2006). 
Sampling was carried out weekly from October 
2005 through December 2007 and, 5 years later, from 
January through December 2013. The number of fish- 
ing boats, number of individual bullnose ray landed, 
and the total weight landed (kilograms) were recorded 
during each visit. Catch per unit of effort (CPUE) was 
defined as the number of individuals caught per trip 
and the total kilograms caught per trip. To identify 
statistical differences in the CPUE between years and 
months (except for 2005, because sample data were 
collected over only 3 months during that year), homo- 
geneity of variances were tested with Levene’s test, 
followed by 2-way fixed-effects analyses of variance 
(ANOVA), based on permutations; all of these analy- 
ses were conducted with Primer 6 1 (PRIMER-E Ltd., 
Ivybridge, U.K.; Clarke and Warwick, 2006) and PER- 
MANOVA+ add-on software for Primer (Anderson et 
al., 2008). When statistical differences were detected, a 
Tukey’s honestly significant difference (HSD) test was 
performed. 
To determine the size-frequency distribution of the 
bullnose ray that were captured and analyzed, the 
disc width (DW), of each individual was measured in 
centimeters; therefore, all subsequent references to 
1 Mention of trades names or commercial companies is for 
identification purposes only and does not imply endorsement 
by the National Marine Fisheries Service, NOAA. 
size in this article refer to DW. Sexes were differenti- 
ated by the presence of claspers in males and their 
absence in females (Conrath, 2005). Differences in the 
proportions of sexes were tested with a chi-square test 
<X 2 ) (Zar, 1996). 
Maturity was determined by macroscopic observa- 
tion of reproductive organs at the landing site. Females 
were considered mature or immature on the basis of 
the presence or absence of fully developed ova in the 
ovaries. Gravid females were recognized by the pres- 
ence of embryos in the uterus, and post-gravid females 
were recognized by the presence of a well-developed, 
large, and highly vascularized uterus (Conrath, 2005). 
For males, maturity was determined by inspecting and 
manipulating claspers. Organisms were considered ma- 
ture when claspers were strongly calcified and could be 
easily rotated around the base (Conrath, 2005). They 
also had to have an extensible distal portion (Conrath, 
2005) and show the presence of seminal fluid (Bizarro 
et al., 2007). Male bullnose ray that lacked these char- 
acteristics were considered to be immature. 
The proportion of males to females at different re- 
productive stages was examined monthly to identify 
the reproductive cycles of the species in the study area. 
Other measurements, such as follicle diameter, uterus 
width, clasper length, gonad weight, and liver weight 
could not be obtained consistently because of the speed 
at which animals were cut and sold on arrival at the 
landing site. 
The median size at maturity was estimated for males 
and females through the use of the logistic function: 
Mf=l/1 + exp _a< C _6) , (1) 
where Mf=the fraction of mature individuals; 
a = the change in slope of M f as a function of the 
size intervals (Li); and 
b =the DW at 50% maturity (DW50). 
Parameter estimates for a and b were obtained by using 
the least squares method with the statistical software 
R, vers 3.1.1 (R Core Team, 2014). A covariance analy- 
sis of these logistic regressions by sexes was performed. 
Results 
For this study, 187 bullnose rays were analyzed. Gen- 
eral characteristics of these specimens are summarized 
in Table 1. The size ranges for all organisms analyzed 
were 22.8-118.0 cm DW and 0.2-19.0 kg. Both average 
DW and average weight increased slightly in recent 
years (Table 1). The size-frequency distribution shows 
that, although the fishery-captured specimens were of 
several size classes, the greatest number of individu- 
als were between 55.0 and 60.0 cm DW (Fig. 1). The 
largest recorded individuals were males; however, only 
4 males were larger than 75.0 cm DW, whereas 25 fe- 
males were found above that size. 
As summarized in Table 2, during the 39-month 
sampling period, 225 fishing trips were analyzed and 
