Species, sex, size and male maturity composition of ... - Seaturtle.org
Species, sex, size and male maturity composition of ... - Seaturtle.org
Species, sex, size and male maturity composition of ... - Seaturtle.org
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18 A. B. M. MOORE ET AL.<br />
substantiated record <strong>of</strong> a devil ray (Mobulidae) from The Gulf (unpubl. data). In<br />
addition, the surveys provided material <strong>and</strong> data on several taxa in need <strong>of</strong> description<br />
or taxonomic resolution that will contribute to an improved underst<strong>and</strong>ing <strong>of</strong><br />
Indo-Pacific Ocean elasmobranch diversity.<br />
PATTERNS OF DIVERSITY AND DISTRIBUTION<br />
Local patterns <strong>of</strong> diversity from this study are difficult to compare quantitatively<br />
when based on samples <strong>of</strong> differing <strong>size</strong>s from l<strong>and</strong>ings <strong>of</strong> different fleets. Based on<br />
a qualitative comparison <strong>of</strong> the data (<strong>and</strong> excluding those species recorded on only a<br />
h<strong>and</strong>ful <strong>of</strong> occasions), Kuwait was notable in that a number <strong>of</strong> species (C. leiodon,<br />
R. oligolinx, R. granulatus <strong>and</strong> A. flagellum) were only recorded there, which may<br />
be due to the proximity <strong>of</strong> the Shatt al Arab. These data <strong>and</strong> those from other studies<br />
indicate geographical differences in the abundance <strong>of</strong> common small carcharhinid<br />
species such as the prevalence <strong>of</strong> C. dussumieri along the coasts <strong>of</strong> Kuwait, Qatar<br />
(this study) <strong>and</strong> Iran (Blegvad, 1944 as Carcharias menisorrah), but relative rarity<br />
<strong>of</strong>f the Omani coast (Henderson et al., 2007; A. Henderson, pers. comm.). Loxodon<br />
macrorhinus was absent from Kuwait in both 2008 <strong>and</strong> 2011 but relatively abundant<br />
in Qatar, Abu Dhabi (this study) <strong>and</strong> in Oman’s l<strong>and</strong>ings (Henderson et al., 2007).<br />
This may be related to this species apparently preferring low turbidity environments<br />
(Gutteridge et al., 2011). Rhizoprionodon oligolinx was only recorded (but relatively<br />
abundant) in Kuwait, where the morphologically similar L. macrorhinus was absent.<br />
Excluding two species recorded as single individuals from Abu Dhabi that had<br />
probably originated from the Gulf <strong>of</strong> Oman [silky shark Carcharhinus falciformis<br />
(Müller & Henle 1839) <strong>and</strong> scalloped hammerhead Sphyrna lewini (Griffith & Smith<br />
1834)] <strong>and</strong> the H. uarnak species complex, the number <strong>of</strong> elasmobranch species<br />
recorded in the current study from The Gulf was 36. Again, excluding H. uarnak,<br />
this is notably less than the 56 reported from Oman (Henderson & Reeve, 2011) <strong>and</strong><br />
largely reflects the lack <strong>of</strong> species associated with deeper waters in the shallow Gulf.<br />
Notable temporal differences were observed in the abundance <strong>of</strong> two species <strong>of</strong><br />
carcharhinid (R. acutus <strong>and</strong> C. sorrah) that were common in Kuwait in 2008 but<br />
were rare or absent at this location in 2011. This absence could be due to a large<br />
number <strong>of</strong> variables, possibly including windy conditions at sea in 2011 reducing<br />
gillnet catches <strong>of</strong> these species, or temporal variation in estuarine discharges affecting<br />
distribution. Surface water temperature was probably not a factor, being similar at<br />
the time <strong>of</strong> both surveys (22·2 ◦ C in 2008 <strong>and</strong> 21·4 ◦ C in 2011, measured at the<br />
same station <strong>of</strong>f east Failaka Isl<strong>and</strong>; F. Al-Yamani, unpubl. data).<br />
SHARK BIOLOGY<br />
There was a highly significant bias towards (mostly mature) <strong>male</strong>s for both<br />
C. dussumieri <strong>and</strong> R. acutus, in both Kuwait in 2008 <strong>and</strong> Qatar. This may be related<br />
to spatial segregation from <strong>male</strong>s by birthing or near-term pregnant fe<strong>male</strong>s, as both<br />
species are reported as having peaks in parturition in spring or summer in the region<br />
(Assadi, 2001; Henderson et al., 2006). Interpretation <strong>of</strong> elasmobranch <strong>sex</strong> ratio data<br />
from l<strong>and</strong>ings is, however, problematic, as any significant differences may be due<br />
to a number <strong>of</strong> confounding factors (e.g. gear bias) as well as natural segregation,<br />
which is commonly reported in elasmobranchs (reviewed in Sims, 2005).<br />
© 2012 The Authors<br />
Journal <strong>of</strong> Fish Biology © 2012 The Fisheries Society <strong>of</strong> the British Isles, Journal <strong>of</strong> Fish Biology 2012, doi:10.1111/j.1095-8649.2011.03210.x