Not just a
huge collection of
Shark
Pictures:
Elasmodiver.com contains images of sharks, skates, rays, and a few
chimaera's from around the world. Elasmodiver began as a simple web
based
shark
field guide
to help divers find the best places to encounter the different
species of sharks and rays that live in shallow water but it has
slowly evolved into a much larger project containing information on
all aspects of shark diving and shark photography.
There are
now more than 10,000 shark pictures and sections on shark
evolution, biology, and conservation. There is a large library of
reviewed shark books, a constantly updated shark taxonomy page, a
monster list of shark links, and deeper in the site there are
numerous articles and stories about shark encounters. Elasmodiver is
now so difficult to check for updates, that new information and
pictures are listed on an Elasmodiver Updates Page that can be
accessed here:
Identification:
Rounded disc. Generally black or chocolate brown
above with scattered, small, irregular, white spots.
Dark coloration is caused by a layer of mucus without which the
dorsum of this species is light brown. Dorsum covered in small
thorns (dermal denticles). Thorns larger towards midline. When
intact, tail roughly 1.5-2 times body disc length. Broad at base,
tapering towards sting, extending into a long thin caudal filament.
Single large spine on tail. Spine and tail filament pale/white.
Ventrum white. Dusky around ventral margin.
Size: Maximum disc width
141cm.
Maximum length with tail 3.5m.
Habitat:
Mangroves, sandy
bays, mixed sand and rubble, lagoons
and near reefs.
From inshore to 85m on the continental shelf.
Distribution:
Wide ranging in the Indo-west Pacific. Known from the Red Sea,
Maldives, India, through Southeast Asia to Australia, PNG and
Micronesia.
Diet:
Adults forage for small fishes including rabbitfishes, gobies,
blennies, wrasses and damselfishes. Juveniles prefer demersal
crustaceans including crabs and shrimps.
Reproduction:
Ovoviviparous. Embryos feed off their yolk sac until
depleted then switch to consuming histotroph; uterine milk secreted
through villi (small projections on the walls of the uterus).
Newborns 14-28cm total length.
Behavior:
Sluggish during the day. The mangrove whipray feeds actively at
night by using its electroreceptors to find prey buried up to 25cm
deep in the sand.
Conservation Status: the IUCN lists
the Mangrove Whipray as globally NEAR THREATENED, . The species' preference for
inshore habitats and the fact that it is apparently uncommon
compared to other Himantura species, makes it particularly
vulnerable to widespread and intensive artisanal and industrial
fisheries operating throughout large areas of its range, as well as
habitat destruction and pollution. Significant destruction and
degradation of mangrove areas and targeting of juveniles in shallow
waters are thought to have significantly affected this species. It
is caught irregularly by tangle net, bottom trawl (including large
numbers of trawlers targeting Rhynchobatids in the Arafura Sea) and
longline fisheries and retained for human consumption. Levels of
exploitation are very high throughout its range in Southeast Asia
and in many parts of the Indian Ocean, hence it is under a severe
level of threat within most of this range. Although no
species-specific data are available, overall catches of stingrays
are reported to be declining in areas of Southeast Asia for which
information is available, with fishermen having to travel further
and further to sustain catch levels. Species that inhabit a similar
range to this species (such as the Sharptooth Lemon Shark (Negaprion
acutidens)) are now rarely observed in Indonesia due to high levels
of exploitation, and significant declines are also inferred to have
occurred in this species in Indonesia and other areas. This species
is assessed as Endangered in Southeast Asia on the basis of inferred
declines (>50%) due to continuing high levels of exploitation.
Fisheries in northern Australia are generally well managed and the
introduction of Turtle Exclusion Devices (TEDs) and other exclusion
devices will have greatly reduced bycatch of this species. The
species is considered at minimal threat throughout its wide range
off northern Australia, where it is assessed as Least Concern.
Globally the species is assessed as Near Threatened, considered
close to meeting the criteria for Vulnerable A2d+A3d+A4d. Further
research is required on life-history characteristics and to assess
catch levels throughout the species range. It will require careful
monitoring and may well qualify for a threat category in the future.
Photographs:
UAE.
Similar
species: Because of its thorny dorsal surface the mangrove whipray could be
confused with the porcupine ray Urogymnus asperrimus.
However, the latter has
far more thorns on a uniformly lighter dorsum and lacks a tail
spine.
Reaction
to divers: Easily approached with slow
non-threatening movements.
Diving
logistics: Seen sporadically throughout its range.
References
and Citations:
Manjaji, B.M., White, W.T.,
Fahmi & Ishihara, H. 2009. Himantura granulata. The IUCN Red
List of Threatened Species 2009: e.T161431A5422325. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161431A5422325.en
. Downloaded on 17 October 2015.
