River Jewels. Chapter 8 - The global status of sharks, rays, and chimaeras.

Abstract

Freshwater or euryhaline sharks and rays are usually a forgotten
component of shark, ray, and chimera biodiversity, mainly
because the vast majority of these species are associated with
marine ecosystems. Freshwater rays are cartilaginous fish species
that have adapted and developed the ability to live and complete
their entire life cycles in freshwater environments (stenohaline),
such as rivers, streams, and lakes.

Full text

INTERNATIONAL UNION FOR CONSERVATION OF NATURE
The global status of sharks, rays,
and chimaeras
Edited by Rima W. Jabado, Alexandra Z. A. Morata, Rhett H. Bennett, Brittany
Finucci, Jim R. Ellis, Sarah L. Fowler, Michael I. Grant, Ana P. Barbosa Martins,
and Sally L. Sinclair

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The global status of sharks, rays,
and chimaeras

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was established by the SSC in 1991 in response to
growing awareness and concern of the severe impact
of fisheries on shark, ray, and chimaera populations
around the world. The SSG is now recognized as
the leading authority on the status of sharks, rays,
and chimaeras and has recently finished assessing
the status of all known species for the second time.
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guest, into partnerships which drive conservation and
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The global status of sharks, rays,
and chimaeras
Edited by Rima W. Jabado, Alexandra Z. A. Morata, Rhett H. Bennett, Brittany
Finucci, Jim R. Ellis, Sarah L. Fowler, Michael I. Grant, Ana P. Barbosa Martins,
and Sally L. Sinclair

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Published by: IUCN, Gland, Switzerland
Produced by: IUCN Species Survival Commission Shark Specialist Group
Copyright: © 2024 IUCN, International Union for Conservation of Nature and
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Citation: Jabado, R.W., Morata, A.Z.A., Bennett, R.H., Finucci, B., Ellis, J.R.,
Fowler, S.L., Grant, M.I., Barbosa Martins, A.P., & Sinclair, S.L. (eds.)
(2024). The global status of sharks, rays, and chimaeras. Gland,
Switzerland: IUCN.
ISBN: 978-2-8317-2318-1 (PDF)
DOI: https://doi.org/10.59216/ssg.gsrsrc.2024
Cover photos: Banded Guitarfish (Zapteryx exasperata) © Jordan Robins/ Ocean
Image Bank; Tasselled Wobbegong (Eucrossorhinus dasypogon) ©
Fabrice Dudenhofer/Ocean Image Bank; Spotted Eagle Ray (Aetobatus
ocellatus) © Amanda Cotton/Ocean Image Bank; Narrownose Chimaera
(Harriotta raleighana) © NOAA Office of Ocean Exploration and
Research, Gulf of Mexico 2017/Flickr.com (CC BY-SA 2.0.); Tiger Shark
(Galeocerdo cuvier) © Hannes Klostermann /Ocean Image Bank; Sand
Tiger Shark (Carcharias taurus) © Simone Caprodossi; Thorny Skate
(Amblyraja radiata) © Andy Murch/www.sharksandrays.com
Back cover: Scalloped Hammerhead (Sphyrna lewini) © Masayuki Agawa/Ocean
Image Bank
Layout: Rima W. Jabado

FOREWORD
EXECUTIVE SUMMARY
ACKNOWLEDGEMENTS
CONTRIBUTORS
NOTES FROM THE EDITORS
1 | INTRODUCTION
2 | BIODIVERSITY, TAXONOMY, AND SYSTEMATICS
3 | ECOLOGY AND LIFE HISTORY CHARACTERISTICS
4 | SOCIO-ECONOMIC SIGNIFICANCE
5 | THREATS
6 | INTERNATIONAL CONSERVATION AND MANAGEMENT INITIATIVES
7 | REGIONAL OVERVIEWS
NORTH AMERICA
Regional introduction
Canada
United States of America
CENTRAL AMERICA AND THE CARIBBEAN
Regional introduction
Antigua and Barbuda
Bahamas
Barbados
Belize
Costa Rica
Cuba
Dominica
Dominican Republic
Dutch Caribbean
El Salvador
French West Indies
Grenada
Guatemala
Haiti
Honduras
Jamaica
Mexico
Navassa Island
Nicaragua
Panama
Saint Kitts and Nevis
Saint Lucia
Saint Vincent and the Grenadines
Trinidad and Tobago
United Kingdom Overseas Territories
United States Overseas Territories
SOUTH AMERICA
Regional introduction
Argentina
Bolivia (Plurinational State of)
Brazil
Chile
Colombia
Ecuador
Falkland Islands (Malvinas)
French Guiana
Guyana
Paraguay
Peru
Suriname
Uruguay
Venezuela (Bolivarian Republic of)
NORTHERN EUROPE
Regional introduction
Belgium
Denmark and its Autonomous Territories
France
Germany
Iceland
Ireland
Netherlands
Norway
Portugal
Russian Federation
Sweden
United Kingdom of Great Britain and Northern Ireland
MEDITERRANEAN AND BLACK SEAS
Regional introduction
Black Sea region
Albania
Algeria
Bosnia and Herzegovina
Croatia
Cyprus
Gibraltar
Greece
Israel
Italy
Lebanon
Malta
Monaco
Montenegro
Morocco
Palestine
Slovenia
Spain
TABLE OF CONTENTS
IX–X
XI–XII
XIII–XIV
XV–XXVIII
XXIX–XXXII
1–4
5–28
29–52
53 –74
75–98
9 9 –116
117–152
119 – 12 0
121–136
137–152
153 –412
153 –160
161–168
169 –182
183–188
189 –196
197–216
217–226
227–232
233–238
239–248
249–258
259–270
271–276
277–286
287–292
293–300
301–306
307–332
333–336
337–346
347–358
359–364
365–370
371–376
377– 388
389–402
403 – 412
413–586
413 – 418
419 – 4 32
433–438
439–456
457–468
469– 478
479– 490
491–496
497– 508
509–520
521–526
527– 542
543–554
555–564
565–586
587–750
587–622
623–636
637–648
649–656
657–664
665–672
673–682
683–692
693–702
703–716
717–726
727–734
735–750
751–994
751–764
765–772
773–780
781–786
787–790
791–798
799–816
817– 822
823–836
837– 844
845–860
861–868
869–882
883–886
887–894
895–904
905 – 914
915–922
923–952
V THE GLO BAL STATU S OF SHA RKS, RAYS, A ND CH IMAE RAS TABLE OF C ONTE NTS VI

State of Libya
Syrian Arab Republic
Tunisia
Türkiye
AFRICA
Regional introduction
Angola
Benin
Cabo Verde
Cameroon
Comoros
Congo
Côte d’Ivoire
Democratic Republic of the Congo
Equatorial Guinea
French Overseas Territories
Gabon
Gambia (Republic of the)
Ghana
Guinea
Guinea Bissau
Kenya
Liberia
Madagascar
Mauritania
Mauritius
Mozambique
Namibia
Nigeria
Sao Tome and Principe
Senegal
Seychelles
Sierra Leone
Somalia
South Africa
Togo
United Republic of Tanzania
United Kingdom Overseas Territories
INDIAN OCEAN
Regional introduction
Bahrain
Bangladesh
Chagos Archipelago
Djibouti
Egypt
Eritrea
India
Iran (Islamic Republic of)
Iraq
Jordan
Kuwait
Maldives
Oman
Pakistan
Qatar
Saudi Arabia
Sri Lanka
Sudan
United Arab Emirates
Yemen
ASIA
Regional introduction
Brunei Darussalam
Cambodia
China
Democratic People’s Republic of Korea (North Korea)
Hong Kong, Special Administrative Region, China
Indonesia
Japan
Macao, Special Administrative Region, China
Malaysia
Myanmar
Philippines
Republic of Korea
Singapore
Taiwan, Province of China
Thailand
Timor-Leste
Viet Nam
OCEANIA
Regional introduction
Australia
Melanesia
Micronesia
New Zealand
Polynesia
POLAR WATERS
Arctic Ocean
Southern Ocean
8 | SPOTLIGHT ON HIGHLY THREATENED GROUPS
Angel sharks
Eagle rays
Gulper sharks
Hammerheads
Longnosed skates
Pelagic sharks and rays
Planktivorous sharks and rays
Rhino rays
River jewels
Tropical stingrays
Walking (epaulette) sharks
Weasel sharks
APPENDIX I – LIST OF COUNTRY CODES
953–960
961–968
969–982
983–994
995 –1398
995–1008
1009–1022
1023 –1030
1031–1042
1043–1052
1053–1066
1067–1078
1079–1086
1087–1092
1093–1098
10 9 9 –111 4
1115 – 113 2
113 3 –11 42
114 3 –11 5 4
115 5 –11 6 4
116 5 –11 76
1177–118 8
118 9 –11 98
119 9 –1 214
1215–1222
1223–1234
1235–1250
1251–1264
1265–1274
1275 –1288
1289–1304
1305 –1318
1319–1326
1327–1338
1339–1356
1357–1368
1369 –1382
1382–1398
1399–1608
1399 –1409
1410 –1416
1417–1424
1425 –1434
1435–1442
1443–1450
1451–1456
1457–1470
1471–1480
1481–1486
1487–1492
1493–1500
1501–1512
1513–1526
1527–1538
1539–1548
1549–1562
1563–1574
1575 –1584
1585–1598
1599–1608
1609–1820
1609–1614
1615–1620
1621–1626
1627–1650
1651–1654
1655–1660
1661–1684
1685–1698
1699 –1704
1705 –1720
1721–1730
1731–174 4
1745 –1754
1755-1768
1769 –1778
1779 –179 8
1799 –1808
1809–1820
1821–1924
1821–1826
1827–1848
1849–1868
1869–1888
1889–1904
1905–1924
1925 –1936
1925 –1931
1932–1936
1937–2070
1937–1944
1945–1954
1955–1964
1965–1978
1979 –1988
1989–1998
1999–2012
2013–2020
2021–2034
2035–2052
2053–2066
2067–2070
2071–2074
VII THE GLOBA L STATUS O F SHAR KS, RAYS, AN D CHIM AERAS TABLE OF C ONTE NTS VIII

2021 THE GLOBA L STATUS OF SHA RKS, RAYS, AND C HIMA ERAS CHAPTER 8 | SPOTLIG HT ON HIGH LY THREATE NED GROU PS 2022
Patricia Charvet
RIVER JEWELS

2023 THE GLOBAL STATUS OF SH ARKS, R AYS, AND CHIM AER AS CHAPTER 8 | SPOTLIG HT ON HIGH LY THREATE NED GROU PS 2024
RIVER JEWELS
Patricia CHARVET
Programa de Pós-graduação em Sistemática, Uso e conservação da Bi-
odiversidade (PPGSis), Universidade Federal do Ceará (UFC), For taleza,
CE, Brazil
João P. FONTENELLE
Institute of Forestry and Conservation, University of Toronto, Toronto,
Ontario, Canada
Getulio RINCON
Curso de Engenharia de Pesca, Universidade Federal do Maranhão
(UFMA), Pinheiro - MA, Brazil
Ricardo de Souza ROSA
Laboratório de Ictiologia (LABICT), Programa de Pós-Graduação em
Ciências Biológicas (Zoologia), Universidade Federal da Paraíba, João
Pessoa, PB, Brazil
Maria Lúcia Góes de ARAÚJO
Laboratório de Ecologia Marinha (LEMAR), Departamento de Engenharia
de Pesca e Aquicultura, Universidade Federal Rural de Pernambuco,
Recife, PE, Brazil
Gregory PRANG
Department of Anthropology, Everett Community College, Everett,
Washington, United States
Yan TORRES
Laboratório de Vertebrados Marinhos (EvolVe), Universidade Federal
do Ceará, Fortaleza, CE, Brazil; Universidade Estadual Vale do Acaraú,
Sobral, CE, Brazil
All authors contributed equally to this section.
SPECIES DIVERSITY, ECOLOGY, AND
DISTRIBUTION
Freshwater or euryhaline sharks and rays are usually a forgotten
component of shark, ray, and chimera biodiversity, mainly
because the vast majority of these species are associated with
marine ecosystems. Freshwater rays are cartilaginous fish species
that have adapted and developed the ability to live and complete
their entire life cycles in freshwater environments (stenohaline),
such as rivers, streams, and lakes (Grant et al., 2022).
Origin, systematics, and taxonomy
Among all living sharks and rays, the Neotropical freshwater
stingrays (subfamily Potamotrygoninae) form the only lineage
that is exclusively obligate to freshwater environments (Thorson et
al., 1978; Rosa, 1985; Lovejoy, 1996; de Carvalho et al., 2016;
Fontenelle et al., 2021a).
The origin of the subfamily Potamotrygoninae has been
hypothesized to have been associated with marine incursion
events from the Caribbean into the northeast portion of South
America (Thorson et al., 1978; Lovejoy et al., 1998, 2006;
Bloom & Lovejoy, 2017; Kirchhoff et al., 2017; Fontenelle et al.,
2021b). However, the age of this freshwater lineage is still a topic
of debate: while most studies using molecular data associate the
origin of the potamotrygonins with the Pebas Wetlands System
during the Oligocene-Miocene (Lovejoy et al., 1998; Albert et
al., 2021; Fontenelle et al., 2021b), some authors estimate an
earlier, Eocene origin (de Carvalho et al., 2004; Adnet et al.,
2014).
Sister to the Potamotrygoninae, the subfamily Styracurinae
comprises two marine whip-tailed stingray species from the
genus Styracura, previously classified as the 'amphi-American
Himantura' (Lovejoy, 1996; de Carvalho et al., 2016). Together,
they form the family Potamotrygonidae, sharing the presence of
angular cartilages (mineralised cartilaginous elements that form
in the ligament articulating the hyomandibula to the Meckel’s
cartilage) as an identifying characteristic for the family, or a
synapomorphy (Fontenelle et al., 2017).
While the earliest mention and descriptive accounts for
Neotropical freshwater stingrays date back to the 16th and 17th
centuries (Rosa et al., 2010), published descriptions of species
now belonging to Potamotrygoninae came only in the 1800s,
allocating freshwater species to marine genera of stingrays (Rosa,
1985; Fontenelle et al., 2021a). The then freshwater exclusive
family Potamotrygonidae was proposed in 1913 to accommodate
all Neotropical freshwater stingray species (Garman, 1913),
which was reclassified as the subfamily Potamotrygoninae with
the description of the sister subfamily Styracurinae (de Carvalho
et al., 2016).
The subfamily Potamotrygoninae currently is composed of
four valid genera: Paratrygon Duméril, 1865; Potamotrygon
Garman, 1877; Plesiotrygon Rosa, Castello and Thorson,
1987; and Heliotrygon de Carvalho and Lovejoy, 2011 (de
Carvalho et al., 2016; Fontenelle et al., 2021a). Molecular
and morphological evidence suggest a closer relationship of
Heliotrygon and Paratrygon, forming its own lineage, as well
as a similar arrangement for the genera Potamotrygon and
Plesiotrygon (de Carvalho & Lovejoy, 2011; Fontenelle & de
Carvalho, 2016; Fontenelle et al., 2017, 2021a). As of 2024,
the subfamily Potamotrygoninae includes a total of 38–39 valid
species (da Silva et al., 2021; Torres et al., 2022b): two in the
genus Heliotrygon, two in Plesiotrygon, three in Paratrygon, and
31–32 in Potamotrygon.
Taxonomy of the potamotrygonins has been fraught with
challenges, which stem from poor and inaccurate early
descriptions, small sample size, and difficult access to specimens
in the wild and in museums, resulting in difficult evolutionary
inferences within this lineage (da Silva & Loboda, 2019;
Fontenelle et al., 2021a; Loboda et al., 2021). Additionally,
potamotrygonins present great variation in inter and intraspecific
colour patterns and external morphologies, making differentiation
of genera and species more difficult, which is reflected in the
noticeable number of species described since the 2000s (Torres
et al., 2022b).
Distribution and habitat
The subfamily Potamotrygoninae is exclusive to South American
freshwater environments, distributed over every major river basin
draining into the Atlantic, except for the São Francisco River and
other coastal basins between the Parnaíba and the Paraná rivers
(Rosa, 1985; de Carvalho et al., 2004; Fontenelle et al., 2021b;
Torres et al., 2022b). Most of the potamotrygonin diversity is
found in the Amazon River basin, followed by the Paraná-
Paraguay basin and the Orinoco basin (Torres et al., 2022b).
Potamotrygonins occupy most continental aquatic habitats
in South America including headwaters, streams, lakes, main
channels, and environments subjected to marine influence, such
as the Amazon estuary and the Maracaibo Lake, a marine tidal
embayment (Rosa et al., 2010). In the Amazon region, they are
found in all three recognised major river types: white (brown
sediment loaded water), clear (bluish or greenish, sediment
poor), and black waters (dark tea-like colour, humic acid rich;
Sioli, 1984).
Biogeographical reconstructions of this subfamily suggest an
early diversification in the region that today corresponds to the
Upper Amazon Region, further invading the Parana-Paraguay
and the Orinoco River basins and then the rivers in the Guyana
and Brazilian shields and the Parnaíba basin (Albert et al., 2021;
Fontenelle et al., 2021b).
Anatomy and morphology
Potamotrygonins, similar to most stingrays, are adapted to
a benthic existence. Their head and body are dorso-ventrally
flattened and their pectoral fins enlarged, extending from the
head to the base of the tail. The undulation of the pectoral fins
provides the swimming locomotory force, but is also used for
excavating burrows in the substratum where they use to hide, as
well as in feeding strategies. The tail is flattened at the base and
usually has one or more series of spines or thorns; it also bears a
venomous sting used for defence, which is commonly involved in
accidents with humans (Rosa, 1985).
Potamotrygonins present mineralised skeletal elements in their
mouth apparatus, more precisely in the ligament between the
Hyomandibular and the Meckel’s cartilage. These angular
cartilages are exclusive to this lineage and hypothesised to
have allowed the exploration of different forms of prey and
environments (Shibuya et al., 2012; Kolmann et al., 2016, 2022;
Fontenelle et al., 2017; Rutledge et al., 2019).
Tooth morphology varies considerably among species,
ranging from triangular teeth with one or more pointed cusps,
found in insectivorous and piscivorous species, to polygonal
teeth with flattened crowns (Herman et al., 1999, 2000), found
in species that consume molluscs and crustaceans (durophagous
diet). Tooth morphology also varies with age, according to the
diet shifts found in several species, as well as with the sex, for
example the teeth of adult males are more pointed than those of
females, and are used during copulatory behaviour (Adnet et
al., 2014; Rutledge et al., 2019; Rincon et al., 2020).
Biology and ecology
The diet of potamotrygonins includes invertebrates such as
insects, annelids, molluscs, crustaceans, and small bony fishes
(Rosa et al., 2010; Shibuya et al., 2012; Kolmann et al., 2016,
2022). Most species have diversified diets, which seem to vary
temporally according to prey availability, age, and sex (Rincon,
2006). Some potamotrygonins show a highly specialised diet,
feeding almost exclusively on a single species of prey (Charvet-
Almeida, 2006; Rosa et al., 2010). Some species, such as the
Parnaiba River Stingray (Potamotrygon signata) Garman, 1913
are mainly insectivorous, feeding on insect larvae and nymphs
(Moro et al., 2012).
Mating in the wild was first reported by Castex (1963),
who indicated a ventral-to-ventral position during copulation,
with the female being constrained by the male against the
substratum. However, Thorson et al., (1983) reported a side-
by-side copulatory position in aquarium observations. As in
other shark and ray species, males use their pointed teeth to
hold on to the female’s pectoral fins, usually leaving scars and
abrasion marks (Thorson et al., 1983; Charvet-Almeida, 2006).
Evidence of multiple paternity has been documented for the
Xingu Freshwater Stingray (Potamotrygon leopoldi; Torres et al.,
2022a) and probably occurs in most other species.
Potamotrygonins bear their embryos until birth, and the latter
are nourished in the uterus by the yolk sac and a secretion referred
to as the uterine milk (viviparity with matrotrophy). Fecundity is
relatively low, varying from one to 21 (exceptional) pups per
litter (Achenbach & Achenbach, 1976). Gestation periods are
estimated to vary between three to 11 months depending on
the different species (Charvet-Almeida et al., 2005; Rosa et al.,
2010).
Capture-stressed pregnant females usually abort to their
young within minutes of capture (Adams et al., 2018). When in a
late stage of development, these aborted embryos have a better
chance of survival and can actively swim after birth (Rincon et
al., 2023). However, they usually remain on the bottom and
absorb the rest of their yolk reserves. The time between capture
Left: Aerial view of the lower portion of the Amazon River
with riverine islands, canals, and sediment-rich waters
Right: The Xingu River rapids, part of the various environments where
freshwater stingrays can be found. The uniqueness of each river
basin and its characteristics usually lead to endemism in freshwater
biodiversity, including in stingrays | Patricia Charvet

2025 THE GLOBAL STATUS OF SH ARKS, R AYS, AND CHIM AER AS CHAPTE R 8 | SPOTLI GHT ON HIG HLY THREAT ENED GRO UPS 2026
and induced embryo abortion is somewhat variable and strongly
dependent on the size of the litter, where larger litters tend to
have a shorter time between capture and abortion (Rangel et
al., 2020).
Neotropical freshwater stingrays are the only group of species
among sharks, rays, or chimaeras which display some maternal
care in the wild. This maternal care behaviour consists of having
the mother remaining still after giving birth to allow the newborns
to swim on top or around her disc for up to over ten hours before
the female leaves and the offspring are on their own (upon
human disturbance, both mother and pups flee). This behaviour
was first documented in the wild for the Ocellate River Stingray
(Potamotrygon motoro; Achenbach & Achenbach, 1976), then
later also observed at least for Wallace’s Freshwater Stingray
(Potamotrygon wallacei), Xingu Freshwater Stingray, and
Smooth Back River Stingray (P. orbignyi), but this has never been
confirmed in captivity possibly due to disturbances in tanks and
environment conditions that differ from the wild. It is uncertain if
this behaviour is restricted to the Potamotrygon genus since its
confirmation remains pending for Paratrygon, Plesiotrygon, and
Heliotrygon (genera with a lower frequency of occurrence). This
display takes place in shallow waters of nursery habitats in the
wild and seems to be associated with reducing predation risk of
neonates right after birth. Therefore, it is possible that it does not
occur in captivity, where the risk of predation is minimised, and
females do not have the need to protect the newborns.
Freshwater stingrays are considered by aquarists as intelligent
and domesticable aquatic pets, since despite their defensive
stinging reaction, they are known to recognise people who care
after them to the point of allowing handling and handfeeding
without expressing any defensive response. Moreover, laboratory
experiments have shown that these species, at least the Ocellate
River Stingray, has the capacity to solve experimental food-
locating tasks in mazes using simultaneously different orientation
mechanisms and strategies (Schluessel & Bleckmann, 2005). This
species also has shown the ability to perceive and discriminate
colours (distinguishing green, blue, yellow, and hues of red)
and have a visual colour system ecologically adapted to their
environment (Schluessel et al., 2021).
Caudal stings are used as a defence mechanism when these
stingrays have their body, mainly the disc region, accidentally
touched or compressed (stepped on) by fishers, or people bathing
or wading in the water. In captivity, it has been documented that
potamotrygonins shed their caudal sting periodically, every three
to four months (Thorson et al., 1988). If not shed, eventually more
than one sting can be observed with up to five caudal stings have
been observed simultaneously. Due to this periodical shedding
and variations in number, caudal stings cannot be used as a
diagnostic feature for taxonomic purposes.
Genetics
Genetic evidence illustrates the systematics and taxonomic
uncertainties that permeate Neotropical freshwater stingrays.
While molecular data corroborate the monophyly of the
Giant Freshwater stingray (Potamotrygon
brachyura) caught by a commercial
fisher in the middle Paraná River. In the
back, the pectoral fins removed from a
processed individual | Mirian G. Baños
subfamily Potamotrygoninae and its two main lineages
(Paratrygon+Heliotrygon and Potamotrygon+Plesiotrygon;
Fontenelle et al., 2021a), generic arrangements and species
diversity incongruences are apparent.
Molecular datasets and phylogenetic inferences of genus level
relationships within Potamotrygoninae suggest a paraphyletic
(meaning species within this subfamily share a common
evolutionary point of descendance, but do not include all species
descended from this point) arrangement between the genera
Potamotrygon and Plesiotrygon, constantly recovering the genus
Plesiotrygon nested within Potamotrygon (Lovejoy et al., 1998;
Toffoli et al., 2008; Garcia et al., 2015; Fontenelle et al., 2021a),
resulting in the paraphyly of Potamotrygon. However, molecular
studies, as of 2024, lack the genetic depth to confidently infer the
phylogenetic position of Plesiotrygon in relation to Potamotrygon
species, and thus fail to reject the monophyly of Potamotrygon
(Fontenelle et al., 2021a).
On the other hand, genetic data provide a resolution regarding
species level relationships that are lacking in morphology-based
studies, which can aid in the investigation of cryptic and/or over-
estimated diversity. The most recent molecular phylogeny of the
Potamotrygoninae (Fontenelle et al., 2021a) highlight the under-
estimated diversity within the genus Paratrygon, describing
genetic lineages that match the species diversity for this genus as
proposed by Loboda (2016) using morphological data.
The scenario is much more complicated in the more diverse
Potamotrygon genus. Molecular evidence indicates the
occurrence of cryptic species diversity within widely distributed
and highly morphologically variable species, such as Ocellate
River Stingray and Smooth Back River Stingray, for example.
These results provide evidence that these nominal species
might act as an umbrella for closely related species with similar
morphologies (Fontenelle et al., 2021a).
Additionally, genetic inferences bring attention to the
possibility of the occurrence of hybridisations between lineages,
where exchange of genetic material between species would
render relationship inferences using this dataset inaccurate.
Alternatively, the phylogenetic incongruences recovered could
represent events of incomplete lineage sorting, which can
be related to accelerated diversification patterns, producing
phylogenetic arrangements that do not fully match the real
evolution of species, due to recent evolutionary paths (Fontenelle
et al., 2021a). Regardless, genetic data highlight that thorough
molecular and morphological studies are necessary to better
interpret the evolution and diversity of this group.
MAJOR DRIVERS OF LOSS
Since freshwater stingrays are restricted to river basins, they
are subject to a greater array of anthropogenic threats than their
marine counterparts.
Freshwater stingrays are subject to threats such as 1)
Ornamental harvest and fisheries: capture pressure
promoted by the illegal trade in Amazonian species for
ornamentation/aquarium trade, artisanal fishing, mainly as
bycatch and negative fishing (eradication or tail mutilation) of
specimens on the beaches during the dry season (de Araújo
et al., 2004; Rincon et al., 2006); 2) Environmental
contamination: result of mining activities in the region
(Rosa, 1987; de Araújo et al., 2004, 2009; Lobo et al., 2016),
petrochemical industry, agricultural, and urbanisation/domestic
effluents; 3) Habitat degradation: deforestation (Sonter et
al., 2017) and fires with consequent soil leaching and siltation of
water courses with lower flow; and 4) Hydroelectric dams:
large, medium, and small hydroelectric dams (Fearnside, 2015),
that fragment populations or restrict their migratory and life
cycle movements, resulting in unpredictable effects on their
populations (Charvet-Almeida et al., 2002; Castello & Macedo
2016).
Ornamental harvest and fisheries
Neotropical freshwater stingrays, particularly species from the
genus Potamotrygon, are highly sought after for the ornamental
fish market (de Araújo et al., 2004). International trade was
unregulated for decades, with fluctuating demand depending on
the species, sex, size, and age. National export quotas (from
Brazil, Colombia, and Suriname) and international quotas (CITES,
2022) represent efforts at regulating and improving sustainability
of international trade in freshwater stingrays. Despite these efforts
in enforcing trade regulation for the group, increased profile and
access to the exotic pet trade through online platforms, including
social media, have presented challenges in regulating the trade
and the traceability of the origin of a specimen. The illegal
market trades species that are either banned from export (e.g.,
Brazil with Pearl Stingray [Potamotrygon jabuti]), or above the
established export quota (e.g., Brazil and Colombia), or above
the allowed export size (e.g., Brazil with the Xingu Freshwater
Stingray between 2003–2006).
The traceability of individuals from cultivation is easier in the
European Union (EU) and the United States (US) than in Asia.
There is a breeding and trade supply out of Asia, which is virtually
unregulated and adds to the opacity of the global source and
trade (Prang, 2020a).
Freshwater stingrays are not usually targeted in artisanal
fisheries. In some areas they are subject to negative fishery
(Compagno & Cook, 1995). This involves tail mutilation or killing
of specimens in 'beach cleaning' associated to tourism (for fear
of sting incidents), mainly affecting species that inhabit sandy
beaches, such as Smooth Back River Stingray. It is common for
fishers to have an aversion to these animals due to a history of
accidents (Casas et al., 2016; Carvalho et al., 2019) or their
interference in fishing activities such as damaging nets and
fishing lines or repelling the target fish and reducing their income
(da Silva et al., 2020). Despite this, the consumption of meat in
specific locations has been documented. Attitudes towards these
rays can be surrounded by prejudices and superstitions (Charvet-
Almeida, 2006; Casas et al., 2016) to the wide consumption
and trade, as observed in Colares, State of Pará (Charvet-
Almeida, 2001). Since 1999, there has been an expansion
of commercial fishing areas along the main-channel of the
Solimões-Amazonas River system, and in the lower Tapajós River
and Purus River, causing a population reduction of species of
the genus Paratrygon (Araújo, 2011). The export of meat from
species, such as Manzana Ray, has been observed in southern
Brazilian markets under the common name cação for sharks
(Camacho-Oliveira et al., 2020).
There is also an unmonitored and unregulated fishery for food.
This has seen a recent increase reported mainly for Manzana Ray
(Paratrygon aiereba) and other larger species of Potamotrygon,
such as Ocellate River Stingray in the Amazon region and Giant
Freshwater Stingray (P. brachyura) taken as a regular animal
protein source in the Paraná-Prata Basin.
Giant Freshwater Stingray carcasses after
capture by a commercial fisher and removal of
pectoral fins for meat in the Paraná River |
Luis O. Lucifora

2027 THE GLOBAL STATUS OF SH ARKS, R AYS, AND CHIM AER AS CHAPTER 8 | SPOTLI GHT ON HIG HLY THREAT ENED GRO UPS 2028
the colouration pattern, size, sex, and final market of the species
(Asia, EU, or North America). Black stingrays such as the Xingu
Freshwater Stingray are worth the most in ornamental trade since
they are breeding matrices. Xingu Freshwater Stingray, also
known as ‘black diamond’, females can cost up to USD 100
more than a male of the same size. There are many males and
few females in the ornamental trade as breeders and wholesalers
place a higher price on females to monopolise brood stock and
increase business expansion potential (Prang, 2020a).
The ornamental trade for freshwater stingrays has changed
in the last 50 years. At the beginning of the stingray export
(1970s–1980s), Brazil’s leading markets for the potamotrygonins
were the US and Europe, followed in the 1990s by Asian
countries such as Japan and Taiwan. In the 1990s, Chinese
economic growth and increased globalisation infrastructure
facilitated increased exports of stingrays to Asian markets. In
subsequent years, European countries, except Germany, started
to occupy positions of less prominence in the list of importing
countries of continental stingrays from South America (Prang,
2020b).
Since the 2010s, Thailand, followed by Hong Kong Special
Administrative Region (SAR), Taiwan, Germany, and the US were
the main import countries of stingrays. In these locations, there
were investments for the development of a culture system for black
ray species (e.g., Tapajós Freshwater Stingray [Potamotrygon
albimaculata], Xingu Freshwater Stingray, and Bigtooth River
Stingray [Potamotrygon henlei]) and for the production of hybrid
and albino individuals. These investments were intensified in
2005, due to the construction of the Belo Monte hydroelectric
power plant, and the possible risk of extinction of Xingu Freshwater
Stingray in the wild. Asian countries saw the cultivation of these
species as a niche business opportunity. The exportation of
freshwater stingrays from South American countries (Brazil,
Colombia, and Peru) currently serves only to replenish the brood
stock in countries like Malaysia and Thailand, similar to what
happened with the species of discus (Symphysodon spp.; Prang,
2020a).
The variety of species is much smaller in the Asian market
compared with other markets (i.e., North America and EU).
However, the variety of hybrids, particularly of Xingu Freshwater
Stingray, is much more significant in Asian markets than in other
markets (Prang, 2020b). The most common stingrays are still
of the black varieties, e.g., Tapajós Freshwater Stingray, Xingu
Freshwater Stingray, and Bigtooth River Stingray, for producing
albino or leucistic individuals (known as albino black diamond
or king henlei) and/or hybrids with Pearl Stingray, Marques’
Freshwater Stingray (P. marquesi), and Suriname Freshwater
Stingray (P. bo ese mani; known as 'white' or 'super white').
Pearl Stingray has a high value because it is easy to hybridise
and produce albino offspring. Ocellate River Stingray (mainly
Colombian specimens) has a high demand because of its lower
price and success in hybridisation. Meanwhile, the European
market continues to preference stingray forms obtained from the
wild (Prang, 2020b).
The Asian markets’ preference for black stingray species
stems from cultural reasons, though not explicitly understood.
In addition to the growing number of hybrid and albino types
on the market, the demand for large individuals has also grown.
Freshwater stingray species in the ornamental trade require an
aquarium system that can support a large animal. In general,
medium to large animals require large water tanks and efficient
water filtering systems to remove ammonia.
Environmental contamination: mining (metal and non-
metal)
Mining and petrochemical activities are the main pollution
threat for the group, due to their harmful and persistent impacts.
Increase efforts of illegal mining in several South American
regions (Lino et al., 2019; Torremorell et al., 2021; Pestana
et al., 2022) raises concern, since the consequences of
contamination from mining effluents can affect reproduction
and survival of potamotrygonin species. Pollution hazards
come not only from these activities; in several South American
river basins, effluents from agricultural fertilisers (leading to
eutrophication and thus less dissolved oxygen in the water)
and pesticides have been detected (Barletta et al., 2019).
Riparian residents from the Parnaíba and Mearim/Pindaré
River basins have reported the use of pesticides in river waters
to reduce potamotrygonin populations in some areas where
stinging accidents were presumably higher. Urban wastewater
containing various and temporally dynamic pollutants is also
a source of pollution. The extent of these pollutants is not yet
fully known, but the known effects on individuals can include
reproductive disorders, and on ecosystems can include hypoxia
and eutrophication (Barletta et al., 2019).
Habitat degradation and pollution (associated to
urbanisation)
The loss of forest cover caused by agricultural and urban
expansion and fires can seriously affect the stability of freshwater
ecosystems and is therefore one of the greatest threats to
Neotropical freshwater stingrays. Loss of vegetation cover is
known to reduce fisheries yields (Castello et al., 2018). Loss of
riparian forests also increases siltation and can alter visibility and
other chemical properties of the water, potentially leading to fast
population declines comparable to overfishing (Barletta et al.,
2015). This process can be of particular concern in blackwater
rivers that rely on nutrient inputs from flooded forests to maintain
their physicochemical properties (Sioli, 1984). An example of this
is the Negro River, where loss of forests to fire severely impacted
the abundance of the endemic Wallace’s Freshwater Stingray
(Araújo, 2022). Due to the inherently intertwined interface of
freshwater and terrestrial ecosystems, impacts on forest cover
need consideration for freshwater stingray diversity.
Hydroelectric dams
Hydroelectric dams are a major problem for potamotrygonins
because freshwater ecosystems are more prone to fragmentation
than marine environments (Castello & Macedo, 2016). Planning
for the near future in Brazil includes the construction of 79 units in
the Legal Amazon, leaving only three tributaries as free flowing
rivers (Castello & Macedo. 2016), which will cause major
impacts on ecosystems, local ecological relationships, riparian
communities, and artisanal fisheries. Of concern is that the present
(2024) hydroelectric dams in the Amazon basin have not
produced the green energy yield as was originally anticipated. It
would be more efficient and less polluting if existing hydroelectric
plants were designed to improve energy efficiency, bearing in
mind that about 25% of the energy produced is lost (Nunes et
al., 2022).
Aquarium Trade and Other Markets
Within the exotic pet trade, there is a very high unit value
for certain species or intra-specific colour patterns variations,
referred to as 'freshwater jewels'. The export value varies with
Xingu Freshwater Stingray P. leopoldi in
an ornamental trader facility awaiting to
be shipped. This is one of the most valued
species of potamotrygonin found in the
international aquarium trade and despite
being bred in farms, demand for wild caught
specimens still exists | Patricia Charvet
Wallacei´s Freshwater Stingray P.
wallacei is a species of freshwater
stingray found in the leaf litter area
of the Rio Itu in the Rio Negro basin |
Ruben Dario Morales Gamba

2029 THE GLOBAL STATUS OF SH ARKS, R AYS, AND CHIM AER AS CHAPTER 8 | SPOTLIG HT ON HIGH LY THREATE NED GRO UPS 2030
There are increasing observations of Potamotrygon spp.
occurring in the wild within Asia because the ornamental trade.
The lack of an adequate system ‘household’ for large individuals
may be contributing to the wild release of individuals. In some
traditional importing countries such as Singapore, the occurrence
of established populations of Ocellate River Stingray has been
reported in local reservoirs (Ng et al., 2010; Hui et al., 2020).
In Taiwan, the Xingu Freshwater Stingray (Liang et al., 2006),
and in China Ocellate River Stingray and Smooth Back River
Stingray (Mu et al., 2008) are considered as invasive species
originating from aquarium discards or escapes. Additionally,
a wild population has been observed in the Brantas River in
Java, Indonesia (Jerikho et al., 2023). While there are no extant
populations of Asia’s freshwater rays in Java, there are concerns
around the potential impacts of the establishment of South
American stingrays in their native ranges, which will require
close monitoring into the future.
CONSERVATION AND MANAGEMENT
National and international regulations
Brazilian Ornamental Export National Regulation:
In Brazil, only six species of the genus Potamotrygon are
allowed for export under the quota system and with limit of
export quantities. This includes Bigtooth River Stingray, Xingu
Freshwater Stingray, Ocellate River Stingray, Smooth Back River
Stingray, Tiger Ray (P. s chroeder i), and Wallace’s Freshwater
Stingray (Instrução Normativa 204, de 22 de outubro de 2008).
Colombian Ornamental National Regulation: In
Colombia, Decree 2256 of October 1991, through the Comité
Ejecutivo para la Pesca (Executive Committee for Fisheries),
determines the species and volumes that may be harvested or
the allocation of annual global quotas. Freshwater stingrays
allowed in the ornamental trade are Manzana Ray, Antenna
Ray (Plesiotrygon iwamae), Rough Freshwater Stingray
(Potamotrygon constellata), Magdalena Freshwater Stingray
(Potamotrygon magdalenae), Ocellate River Stingray, Smooth
Back River Stingray, and Tiger Ray (Sanchez-Duarte et al.,
2014). A quota of 23,000 animals was established annually for
the years 2012–2014, following a significant increase in exports
in the period from 2006–2008 (Ajiaco-Martinez, 2012).
Regulation for Suriname Freshwater Stingray: in
Suriname an export quota was established for the endemic
Suriname Freshwater Stingray (Verheij, 2019).
The presence of potamotrygonins in the appendices of the
Convention on International Trade in Endangered Species
of Wild Fauna and Flora (CITES) is marked by two temporal
milestones. Firstly, the subfamily Potamotrygoninae (then referred
to as Potamotrygonidae) was included in CITES Appendix
III in 2017. This was primarily to improve the quality of trade
data (CITES, 2017). Moreover, the aforementioned document
identified five species (Manzana Ray, Xingu Freshwater
Stingray, Tiger Ray, Giant Freshwater Stingray, and Ocellate
River Stingray) as being of priority concern.
Since illegal international trade had not ceased despite Parties
efforts to establish management measures, in 2022, Xingu
Freshwater Stingray and Wallace’s Freshwater Stingray, along
with their lookalikes (Bigtooth River Stingray, Tapajós Freshwater
Stingray, Pearl Stingray, Marques’ Freshwater Stingray, and
Parnaiba River Stingray), were included in CITES Appendix II.
Consequently, it is expected that the listing of these species
would serve as an essential instrument to inhibit international
illegal trade, improving specimens export/import control and
ensuring that the removal of individuals from the wild is done
under sustainable levels.
RECOMMENDATIONS
Freshwater stingray management and conservation can be
quite challenging since the ornamental harvest and trade has
led to ‘invasive’ ranges of some threatened species, while other
species remain threatened in their natural range. Moreover,
there are highly valued species which contrasts with the
negative fisheries of riparian residents in other regions. Along
with ornamental harvest and trade, there is a need to continue
building our understanding of other pressures to wild populations
including food and negative fisheries, habitat degradation,
pollution, construction of barriers to waterflow, and the potential
compounding potential of climate change.
Freshwater stingray conservation measures should include
fisheries management and prioritise preservation of the integrity
of their habitats. As of 2024, four species have their populations
severely impacted by significant changes in habitat such as
Wallace’s Freshwater Stingray (Araújo, 2022), Xingu Freshwater
Stingray (Charvet, 2022), Magdalena Freshwater Stingray
(Lasso et al., 2012), and Tiger Ray (Ajiaco-Martinez et al, 2012).
There is no public policy to protect habitats of Potamotrygon
species, and the existing conservation measures are insufficient
to ensure the sustainability of some wild populations. The other
three genus face similar challenges, mainly Heliotrygon, which is
less abundant in nature than any other potamotrygonin.
Finally, freshwater rays are much more susceptible to threats
associated with habitat degradation or loss than their marine
counterparts. Specific management and conservation measures
are urgently required for many potamotrygonin species.
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areas | Patricia Charvet

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A diaphanized Potamotrygon specimen. This
technique is used in skeletal structures studies when
soft tissues are digested with enzymes and specific
stains applied to color more resistant (orange-reddish
hues) and softer (blueish hues) cartilages | André Casas