The IUCN/SSC Shark Specialist Group
Shark News 14: March 2002
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Neotropical Freshwater Stingrays: diversity and conservation status
Patricia Charvet-Almeida1, Maria Lúcia Góes de Araújo2, Ricardo S. Rosa3 and Getúlio Rincón4
1MPEG, Belém; 2UA, Manaus; 3UFPB, João Pessoa; 4UNESP, Rio Claro, Brazil
(the authors' name sequence does not indicate priority in the contribution to this article).
Diversity
The family Potamotrygonidae, Garman 1877 is comprised of freshwater
stingrays with geographical distribution restricted to South America.
They occur in several river basins draining into the Atlantic Ocean, and
a few species enter estuarine waters. The taxonomic status of the group
has been subject to debate in the recent literature, with some authors
regarding it as a monophyletic family (Thorson et al. 1983, Rosa et al.
1987, Lovejoy 1996), while others treat it as part of the Dasyatidae,
either as a subfamily (Nelson 1994) or as a paraphyletic assemblage
(Nishida 1990). The taxonomic composition of the Potamotrygonidae
was revised by Rosa (1985), who reported 32 species clearly assigned to
this family, 20 of which were considered valid species in three distinct
genera, namely Plesiotrygon, Potamotrygon and Paratrygon. This taxonomic
arrangement has been followed by subsequent authors (Eschmeyer 1998,
Compagno 1999) although Rosa and others have presented evidence
of several undescribed species (Rosa 1985, Carvalho 2001), and of at
least one undescribed genus (Ishihara and Taniuchi 1995, Compagno
1999, Charvet-Almeida and Rosa 2001).
Potamotrygon leopoldi, searching for food in its natural habitat. This is one of the most valuable species in the ornamental fish market. Photo: Patricia Charvet-Almeida.
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Fisheries
Historically, freshwater stingrays were not valuable to Amazon fishermen
as food fish (Ferreira 1886). Nonetheless, these rays are routinely
captured as a food resource in some regions of the lower Amazon
drainage. In addition, during the last 15 years they have become
important as ornamental fish, comprising 1 % of the total ornamental
fish exports from Manaus (Amazonas State), with at least six species
regularly exported for this purpose. Potamotrygon motoro, P. orbignyi,
P. schroederi, P. leopoldi, P. henlei and Potamotrygon sp. comprise
67% of all freshwater stingrays exported from Manaus, and the latter
three species are endemic to areas where gold mines, dams, and large
ecotourism projects are in progress. Twenty thousand freshwater
stingrays are now exported annually from Brazil. Around 57 % are from
the Rio Negro Basin (Amazonas State). Despite this demand, the
Brazilian Environmental Agency (IBAMA) has no fishery or exportation
records for these species from this area. Specimens from other areas are
often incorrectly identified and export numbers are certainly
underestimated. Nowadays, P. leopoldi and P. henlei are in fact
illegally exported from Brazil. Some other species, from the Amazonas
State, are being exported according to law number 022/98 (IBAMA
2001) that establishes a quota system
for each export authorised species.
The most important countries
involved in the Potamotrygonidae trade
are the United States, Japan, Taiwan
and Germany, where these stingrays
are sold in pet shops according to codes
that represent a particular colour pattern
rather than a species.
Accidents involving freshwater
stingrays are common in most Amazon
Basin rivers. Painful results of these
accidents certainly make these stingrays
extremely non-charismatic and feared
animals for local residents and visitors.
It has been estimated that in the last
three years at least 21,000 stingrays
have been removed from the population
as a direct result of the tourism industry,
with agencies hiring people to "cleanup"
the river beaches by killing the
stingrays prior to the arrival of tourists.
Mutilation of specimens has also been observed. Unfortunately, given
that the removal of stingrays in this way does not represent "fishing" as
such, IBAMA has been unable to control it.
Case study of the Tucuruí Dam
The present Brazilian electrical crisis and the subsequent demand
for the construction of hydroelectric powerplants has raised questions
about the effects of dams on freshwater fishes, especially stingray
populations. Currently there are 21 dams under
construction, and Brazilian scientists are running
against time in order to collect as much biological
and ecological data as possible, to measure the
effects on fish populations. The Tucuruí Dam,
closed in 1984, has completely prevented the
interchange of stingrays between the Tocantins
and Pará rivers.
The Tocantins River is also home to the
endemic stingray species Potamotrygon henlei, a
precious black and white spotted ray for aquarists.
Seventeen years since the dam closure, local
fishermen report that piranhas and stingrays,
especially P. henlei, have increased abruptly in number,
while some teleosts have disappeared and others decreased
in size. The stingrays (P. henlei) have learned to eat the meshed
fishes caught in the gillnets, and fisherman do not kill them since their
meat has no commercial value in the region. Although preliminary
evidence indicates a positive situation for P. henlei in the reservoir
area, the same cannot be confirmed for P. orbignyi or Paratrygon
aiereba, since the implications of the interrupted genetic flux between
Tocantins and Amazonas populations can only be speculated at this
time.
Potamotrygon motoro, a widely distributed species used for ornamental purposes. Photo: Maria Lúcia G. Araújo.
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Ecology and Conservation
Until recently, the life history parameters of potamotrygonid stingrays
were virtually unknown, despite the fact that they have already been
fished for decades, increasingly for the international ornamental fish
trade market. Several species remain undescribed but are being traded
and kept by freshwater hobbyists from all over the world.
Lasso et al. (1997), Araújo (1998) and Charvet-Almeida (2001)
provided information on reproduction and the general biology of
several species. The lack of adequate life history parameters for most
species of this family prevents precise assessments of their conservation
status. On the other hand, direct evidence of impacts on natural
populations, including habitat degradation from river damming and
mining, as well as the ornamental fisheries pressure has led to preliminary
concern for several species. The effect of these activities on the
populations is far from being well understood. So far, five species have
been cited in the IUCN (2000) Red List as threatened species.
The importance of freshwater stingrays to the ornamental fish
industry in the Amazon Region can no longer be ignored because the
international demand for these species is growing (Brooks 1995). The
hobbyists determine the demand for these fishes and direct the fishing
effort. A management plan for this fishery must consider the complex
chain that involves the subsistence of the fishermen, the interest of the
hobbyists, the environmental conditions in freshwater stingray habitats
and the limitations of the life history of each species.
References
Araújo, M. L. G. 1998. Biologia Reprodutiva e Pesca de Potamotrygon
sp. C (Chondrichthyes - Potamotrygonidae), no Médio Rio Negro,
Amazonas. Unpublished dissertation. Instituto Nacional de
Pesquisas da Amazônia & Universidade do Amazonas, Manaus.
Brooks, D. R. 1995. Neotropical freshwater stingrays and their parasites:
a tale of an ocean and a river long ago. In: Oetinger, M. I. and G.D.
Zorzi (eds.). The Biology of Freshwater Elasmobranch. Journal of
Aquariculture and Aquatic Sciences 7:52-61.
Charvet-Almeida, P. 2001. Ocorrência, Biologia e Uso das Raias de
Água Doce na Baía de Marajó (Pará, Brasil), com Ênfase na
Biologia de Plesiotrygon iwamae (Chondrichthyes:
Potamotrygonidae). Unpublished dissertation. Universidade
Federal do Pará & Museu Paraense Emílio Goeldi. 213 pp.
Carvalho, M. 2001. An overview of the taxonomy
of Neotropical freshwater stingrays
(Chondrichthyes: Myliobatiformes:
Potamotrygonidae). Abstracts of the Joint
Meeting of Ichthyologists and Herpetologists.
American Society of Ichthyologists and
Herpetologists. Pennsylvania State University,
State College, PA.
Charvet-Almeida, P. and R.S. Rosa. 2001. A New
Genus and Species of Freshwater Stingray
(Potamotrygonidae) from the Lower Amazon
Drainage. Abstracts of the Joint Meeting of
Ichthyologists and Herpetologists. American
Society of Ichthyologists and Herpetologists.
Pennsylvania State University, State College,
PA, USA.
Compagno, L. J. V. 1999. Checklist of living elasmobranchs. In: Sharks,
skates and rays, the biology of elasmobranch fishes. W. C. Hamlett
(ed.). The John Hopkins University Press, Baltimore. p. 471-498.
Eschmeyer, W. N. 1998. Catalogue of fishes. California Academy of
Sciences. San Francisco.
Ferreira, A. R. 1886. Viagem Filosófica ao Rio Negro. Revista do
Instituto Histórico Geográfico Brasileiro, XLIL (1):123-188.
IBAMA - Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais
Renováveis. 2001. Portaria no 022/98.
Ishihara, H. and T. Taniuchi. 1995. A strange potamotrygonid ray
(Chondrichthyes: Potamotrygonidae) from the Orinoco River
system. In: Oetinger, M. I. and Zorzi, G. D. (eds.). The Biology of
Freshwater Elasmobranch. Journal of Aquariculture & Aquatic
Sciences 7:91-97.
IUCN. 2000. 2000 IUCN Red List of Threatened Species. Compiled by
C. Hilton-Taylor. International Union for Conservation of Nature
and Natural Resources. Gland, Switzerland and Cambridge, UK.
Lasso, C. A., A.B. Rial and O. Lasso-Alcalá. 1997. Notes on the biology
of the freshwater stingrays Paratrygon aiereba (Müller and Henle
1841) and Potamotrygon orbignyi (Castelnau 1855)
(Chondrichthyes: Potamotrygonidae) in the Venezuelan llanos.
Acqua, 2(3):39-50.
Lovejoy, N. R. 1996. Systematics of myliobatid elasmobranchs: with
emphasis on the phylogeny and historical biogeography of
neotropical freshwater stingrays (Potamotrygonidae: Rajiformes).
Zool. J. Linn. Soc. 117:207-257.
Nelson, J.S. 1994. Fishes of the world. New York, John Willey & Sons.
Nishida, K. 1990. Phylogeny of the Suborder Myliobatidoidei. Mem.
Fac. fisher. Hokkaido Univ. 37:1-108.
Rosa, R. S. 1985. A systematic revision of the South American freshwater
stingrays (Chondrichthyes: Potamotrygonidae). Unpublished
doctoral dissertation. The College of William and Mary,
Williamsburg. 523 pp.
Rosa, R. S., H. Castello and T.B. Thorson. 1987. Plesiotrygon iwamae,
a new genus and species of Neotropical freshwater stingray
(Chondrichthyes: Potamotrygonidae). Copeia 2:447-458.
Thorson, T. B., D. R. Brooks and M. A. Mayes. 1983. The evolution of
freshwater adaptation in stingrays. Nat. Geog. Res. Reports 15:663-
694.
Patricia Charvet-Almeida
Rua Mundurucus
2445 ap.1202-Batista Campos
Belem-Para, 66040-270
Brazil
Email: pchalm@nautilus.com.br
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