Tagliafico et al. Exploitation and reproduction of Aetobatus nannari in the Los Frailes Archipelago, Venezuela 
313 
In our study of the small, directed fishery in north- 
eastern Venezuela, data required to analyze fishing 
effort by considering the effects of net size, effective 
fishing time, and other factors, such as depth and 
location, were not collected. Hence, effort was ex- 
pressed in number of trips, which is likely a biased 
estimate of effective fishing effort. In any case, the 
time series analyzed is too short to infer changes in 
population abundance. Almost 40 years ago, Gines et 
al. (1972) mentioned that the overall abundance of 
rays, including the spotted eagle ray, in northeastern 
Venezuela had decreased. Decreases in abundance 
of A. narinari also were mentioned for the Colom- 
bian Caribbean (Correa and Manjarres, 2004); the 
northern Gulf of Mexico (Shepherd and Myers, 2005), 
where it was last observed in 1980 in autumn de- 
mersal trawl surveys; and Campeche Bank in the 
southeastern Gulf of Mexico (Cuevas-Zimbron et al., 
2011), as well as globally for the A. narinari species 
complex. Nevertheless, our study area is apparently 
part of an important concentration area for A. nari- 
nari in the Caribbean. This species may do better in 
this area than in other areas in the western Atlantic, 
because large populations of bivalve and gastropod 
mollusks, which constitute the main food items in 
the diet of A. narinari (see Randall, 1967), are pres- 
ent in northeastern Venezuela (Gines et al., 1972; 
Lodeiros-Seijo and Freites-Valbuena, 2008). 
Length structure and length-weight relationships 
In our study, females attained sizes larger than 
the sizes reached by males and were much more 
abundant than were males at lengths >160 cm DW. 
Differences in length distributions by sex have 
been reported in other areas of this species’ range 
(Cuevas-Zimbron et al., 2011). Additionally, growth 
studies on A. narinari indicate that females grow 
more slowly and reach larger sizes than do males 
(Dubick, 2000). 
Males and females appear to be fully recruited to 
the fishery at 140 and 150 cm DW, respectively. Of 
A. narinari captured under 140 cm DW, -37% were 
male and 19% were female. For both sexes, individuals 
<100 cm DW were rarely found in the fishery in the 
Los Frailes Archipelago. This absence may result from 
the selectivity of fishing gear or differential distribu- 
tion of juveniles and adults. In the directed fishery in 
the southeastern Gulf of Mexico (Cuevas-Zimbron et 
al., 2011), mesh openings (30.5-36.5 cm extended) are 
similar to the mesh sizes of nets used in northeastern 
Venezuela. However, despite the similar mesh openings 
used in both areas, A. narinari in the southeastern 
Gulf of Mexico, observed at lengths of 44-202 cm DW, 
included a higher proportion of juveniles than did the 
A. narinari observed in the Los Frailes Archipelago. 
Also, Cuevas-Zimbron et al. (2011) reported size segre- 
gation in relation to distance from shore and depth in 
the southeastern Gulf of Mexico, with larger individu- 
als predominating at distances of 30-50 km offshore 
t: 
o 
Q. 
Disc width (cm) 
Figure 4 
Length at maturity logistic functions for (A) male and 
(B) female individuals of Aetobatus narinari in the Los 
Frailes Archipelago during the period from August 2005 
to December 2007. Horizontal and vertical lines indicate 
estimated length at 50% maturity (L 50 ) and value of L 50 
is given. 
(depths of 8-12 m) and smaller individuals predomi- 
nating at distances of 8-15 km offshore (depths of 6-8 
m). In northeastern Brazil, neonates and juveniles of 
A. narinari were caught close to the shore in shallow 
depths <10 m (Yokota and Lessa, 2006). Considering 
these results by Cuevas-Zimbron et al. (2011) and Yo- 
kota and Lessa (2006) and considering that the typical 
height (8-10 m) of nets used around the Los Frailes 
Archipelago precludes their use in shallower waters, 
it is likely that differential distribution of juveniles 
and adults in relation to the fishery in northeastern 
Venezuela explains the absence of small individuals 
in our samples. 
There were no significant statistical differences in 
the length-weight relationships of male and female A. 
narinari. To our knowledge, our study is the first re- 
ported comparison of this relationship for this species. 
