DIVERS

FEATURE CREATURE
FEATURE CREATURE
FEATURE CREATURE
BOWMOUTH GUITARFISH ( RHINA ANCYLOSTOMA)
FEATURE IUCN RED LIST 2016 PHOTOGRAPHY ANDY MURCH | WWW.ELASMODIVER.COM
RED LIST CATEGORY & CRITERIA:
VULNERABLE
Scientific Name: Rhina ancylostoma
Common Name(s): Bowmouth Guitarfish,
Shark Ray, Mud Skate
Taxonomic Source(s): Last, P.R., Séret, B. and
Naylor, G.J.P. 2016. A new species of guitarfish,
Rhinobatos borneensis sp. nov. with a redefinition
of the family-level classification in the order
Rhinopristiformes (Chondrichthyes: Batoidea).
Justification: The Bowmouth Guitarfish (Rhina
ancylostoma) is a widely distributed inshore
species of the Indo-West Pacific. This species
is taken by multiple artisanal and commercial
fisheries throughout its range, both as a
target species and as bycatch. Flesh is sold for
human consumption in Asia and the fins from
large animals fetch exceptionally high prices,
creating a significant incentive for bycatch to
be retained.
Very little is known about the biology or
population status of this species, but it appears
not to be common anywhere. Estimated
generation length (7.5 years) is moderate but
this is based on proxy data and needs to be
verified. Given its susceptibility to capture by
multiple fishing gear types, including trawl nets,
gillnets and hooks, and its high value fins, it is
inferred that numbers have been locally reduced
by fishing throughout its range. Local population
depletion can be inferred from Indonesia
where the target gillnet fishery fleet for rhinids
and rhynchobatids has declined significantly,
reportedly due to declining catch rates (>50%
over 3 generations). It is probable that the
population will continue to decline, at least, until
target fisheries become uneconomical. Habitat
destruction is also thought to pose a significant
threat to the Bowmouth Guitarfish throughout
much of its range.
Based on its shallow water habitat
preferences, its susceptibility to capture, high
value fins, continual fisheries pressure placed
across most of its range, global declines in
chondrichthyan landings of at least 20% over
the past 12 years, and the fact that the Indo-
West Pacific is a region with some of the
most poorly managed and intensely fished
waters, a population reduction of greater
than 30% over three generations is inferred
for the Bowmouth Guitarfish, resulting in an
assessment of Vulnerable.
In Australian waters, this species is classified
as Near Threatened (close to meeting VU
A2c+A3c). There are no target fisheries for
the Bowmouth Guitarfish in Australia but it
is a known bycatch species in demersal trawl
fisheries. The introduction of turtle exclusion
devices (TEDs) in Australian trawl fisheries and
the implementation of various elasmobranchfinning
prohibitions has probably led to a recent
reduction in captures by this sector. However,
the lack of information about the species,
suspected longevity and low reproductive rate,
and high economic value support an assessment
of Near Threatened, and the situation should be
monitored due to the suspected vulnerability of
this species and the high value of its fins.
Previously published Red List assessments:
2003 – Vulnerable (VU)
Range Description: The Bowmouth Guitarfish
is wide-ranging in the Indo-West Pacific from
East Africa (Red Sea to South Africa) to Papua
New Guinea, north to Japan, across northern
Australia from Shark Bay in Western Australia
to Sydney in New South Wales, and east to
New Caledonia (Last and Stevens 2009, Fricke
et al. 2011).
Countries occurrence: Native: Australia (New
South Wales, Northern Territory, Queensland,
Western Australia); Bahrain; Bangladesh; China;
Djibouti; Egypt; Eritrea; India; Indonesia (Jawa,
Kalimantan); Iran, Islamic Republic of; Japan;
Kenya; Korea, Democratic People’s Republic
of; Korea, Republic of; Kuwait; Madagascar;
Malaysia; Mozambique; New Caledonia; Oman;
Pakistan; Papua New Guinea; Philippines;
Qatar; Saudi Arabia; Seychelles; Solomon
Islands; Somalia; South Africa (KwaZulu-Natal);
Sri Lanka; Sudan; Taiwan, Province of China;
Tanzania, United Republic of; Thailand; United
Arab Emirates; Vietnam; Yemen.
FAO Marine Fishing Areas: Native: Indian
Ocean – eastern; Indian Ocean – western;
Pacific – northwest; Pacific – western central;
Pacific – southwest.
Lower depth limit (metres): 90
Population: Globally, shark and ray landings
have declined by at least 20% since 2003, but
the Indo-Pacific is amongst the regions where
this decline has been more severe (Dulvy et al.
2014). Catches of sharks and rays in Southeast
Asia are very high but are declining and fishers
are travelling much further from port in order
to increase catches (Chen 1996). Net and
trawl fisheries in Indonesia (especially the Java
Sea) and elsewhere are very extensive and as
a result, many shark and ray species are highly
exploited and stocks of most species have
declined by at least an order of magnitude
(Blaber et al. 2009). Batoids are heavily
exploited (White and Dharmadi 2007) and
datasets from as early as 1963–1972 show
the considerable decline in batoids in the Gulf
of Thailand (Pauly 1979). Trawl and gill net
fisheries are also moving further afield. For
example, in Jakarta the gillnet fishery at Muara
Baru travels to waters around Kalimantan due
to the decline in local populations (W.T. White,
unpubl. data).
While species-specific data on long-term
declines in elasmobranchs in the Southeast Asian
region are lacking, declines of the Bowmouth
Guitarfish in Southeast Asia and elsewhere in
the Indo-West Pacific are inferred given the
widespread historical and continuing declines
of demersal fisheries in this region (Stobutzki
et al. 2006). Furthermore, the extensive loss
and degradation of habitats such as coastal
mangroves are another key threat to coastal
and inshore species; Southeast Asia has seen
an estimated 30% reduction in mangrove area
since 1980 (FAO 2007, Polidoro et al. 2010).
Current Population Trend: Decreasing
Habitat and Ecology: The Bowmouth Guitarfish
has a coastal distribution throughout its range,
generally occurring close inshore and around
coral reefs to about 90m (Anonymous 2003,
Fricke et al. 2011). It occurs on or close to the
seabed, mainly over sandy or muddy substrates.
Very little is known about the life history
characteristics of this species. However, it is a
large species growing to at least 270cm total
length (TL) and is lecithotrophic viviparous
(Compagno and Last 1999).
Males mature between 150 and 175cm TL,
and one pregnant female was recorded with 9
mid-term embryos ranging between 27-31cm
TL (Last and Stevens 2009). A single new born
individual of 51cm TL has been observed (Last
et al. 2010). Further research on the biology, life
history and exploitation of this species is needed.
Generation length is unknown. The Giant
Shovelnose Ray (Glaucostegus typus) grows to a
similar size and is a related species and using it as
a proxy species, generation length is estimated
to be 7.5 years which is moderate compared to
other elasmobranchs (White 2014). However,
this must be applied with caution as Bowmouth
Guitarfish is in a monophyletic family with no
co-generic species.
Systems: Marine
Generation Length (years): 7.5
Use and Trade: When caught in Asia, it is
often marketed locally for fins which are very
valuable. This species is landed in Madagascar
and Saudi Arabia but appears to be a very
minor component of the catch (Robinson
and Sauer 2013, Spaet and Beruman 2015).
It has also been recorded in catches in India
(Theivasigamani and Subbiah 2014) although
the number taken in Indian fisheries is unclear.
This species is a popular display animal in
commercial aquaria (Last and Stevens 2009).
Major Threat(s): The Bowmouth Guitarfish is
one of the target species of Southeast Asian
rhinid and rhynchobatid gillnet fisheries (W.T.
White, pers. comm., 2003), which are generally
unregulated and catches are thought to be
poorly recorded (Chen 1996). The target
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