PConservation of freshwater fish biodiversity : a challenge for

W
Sheet n°290 - March 2008
Conservation of freshwater fish biodiversity :
a challenge for the countries of the South
P
sent and move around
rapidly on all the continents, human activity
has become a significant
vector for the spread
of species beyond the
range of their native
ecosystem. However,
no global-scale scientific study had yet managed to measure the human influence involved
in the establishment
of a complete group
of non-native species
within a given natural
environment. Work recently published by an
international team1, including research scientists from the University Paul Sabatier of
Toulouse, the IRD and
the CNRS, yielded the
first global-scale appreciation of the processes
leading to freshwater
fish invasion in river
basins. The investigation, conducted on over
1000 rivers harbouring 10 000 freshwater
fish species, showed
that the colonization
by non-native species
stemmed mainly from
human activities. This
phenomenon
affects
predominantly all river
ecosystems of countries of the Northern
hemisphere. However,
in the context of economic growth developing
countries are now experiencing, their river basins, home to the greater part of freshwater
fish biodiversity, are at
risk of the same fate unless vigilance is applied.
© Onema / F. Storck
ver since humans
E
have had technology
enabling them to be pre-
Originating from North America, the pumpkinseed sunfish (Lepomis gibbosus) is now present
in most of Europe’s river systems.
Humans have regularly been introducing
exotic species into natural environments
in order to provide for their nutritional
necessities or meet less indispensable
purposes such as horticulture, fishing
or hunting. However, the particular
environments are not always adapted for hosting new arrivals. Past
introduction attempts, such as that of
wild rabbit into Australia or brown fario
trout into Southern hemisphere water
courses, led to an awareness that these
different species, qualified by scientists
as none-native, have the power to upset
an ecosystem. The 2002 Convention on
Biodiversity recognized that the species
introductions can cause regression of
biological diversity, following destruction
of natural habitats. Although it has long
seemed likely that human activity plays
a major role in such effects, no scientific
study had yet yielded measurements of
its involvement at planetary scale for a
given group of species. An international
research team comprising IRD, CNRS
and University of Toulouse scientists
recently published a study that gave
the first real demonstration that human
activity is the main driving factor behind
the establishment of exotic fish species
populations in river ecosystems. Examination of data on presence of around
10 000 freshwater fish in 1055 river basins covering both 80% immersed lands
and 80% of globally recorded freshwater fish species allowed identification
of seven species-invasion hot-spots :
the Pacific coast of North America and
Central America, Patagonia, southern
and western Europe, South Africa and
Madagascar, central Asia, the South of
Australia and New Zealand (See Map).
These regions are characterized by river
basins where non-native species make
up more than one quarter of the freshwater fish species recorded. Moreover,
they are superimposed on biodiversity
hot-spots which correspond to geographical zones a strong endemism rate
and a very high total number of species.
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CONTACTS :
FABIEN LEPRIEUR
Laboratoire Evolution et
diversité biologique
Adresse : Université Paul
Sabatier, bâtiment 4R3
115 route de Narbonne
331062 Toulouse cedex 4
France
Tél : +33 (05) 61 55 67 47
[email protected]
THIERRY OBERDORFF
Directeur de recherche
IRD
Unité de recherche
Approche macro-écologique de la biodiversité
aquatique en zone
continentale
(AMAZONE)
Adresse : MNHN
43 rue cuvier
75005 PARIS
Tél : +33 (0)1 40 79 37 67
[email protected]
REFERENCE :
FABIEN LEPRIEUR, OLIVIER
BEAUCHARD, SIMON BLANCHET, THIERRY OBERDORFF,
SÉBASTIEN BROSSE, Fish
Invasions in the World’s
River Systems : When
Natural Processes Are
Blurred by Human Activities, PloS Biology, 2008,
Vol. 6, No. 2, e28
doi : 10.1371/journal.
pbio.0060028
KEY WORDS :
The team also sought to determine the
extent of the relative influence of the
particular characteristics of each ecosystem and human activities on the diversity of the non-native fish species.
Three hypotheses were tested : the
“biotic resistance”, “biotic acceptance”
and “human activity”. The first suggests
that a high diversity of freshwater fish in
the host ecosystem acts as a barrier to
the establishment of non-native fish specie populations. The second postulates
conversely that, for a given ecosystem,
non-native species diversity follows that
of native species because favourable
ecological conditions for the latter are
also suitable for the newly arrived species. As for the third, it takes account
of the different indicators at river-basin
scale (gross domestic product, percentage of land urbanized, population
density), that can yield determination
of the relation between anthropic pressure and non-native species diversity.
The three hypotheses’ relative weight was measured using statistical
methods. For the whole set of river
basins investigated, the environmental
conditions of fluvial ecosystems were
found to have practically no influence
on the exotic species diversity. On the
contrary, it is the human factors, and
especially the intensity of economic
activities –measured by the GDP,
which determine the number of nonnative species present in a river basin. These results thus suggest that the
economic development foreseen in the
developing countries should be accompanied by a rise in the number of nonnative freshwater fish species. Given
that biological invasions are considered
as one of the main causes of biodiversity loss, such a scenario would probably
be detrimental to the aquatic biodiversity conservation of these regions. This
study indicates that exceptional river
ecosystems, like the Amazon Basin in
South America or that of the Congo in
central Africa, are still hardly affected by
species introduction. For example, no
more than 1% of the 3000 species of
fish recorded in the River Amazon are
non-native species. Just as a considerable number of countries of the South
are seeing their economic growth take
off, this kind of study should be useful
in the future for setting up an effective
watch system for the surveillance of the
exotic species colonizing the most biodiversity-rich natural environments and
make it possible to apply the principle of
precaution before they become invasive.
Grégory Fléchet – DIC
Translation : Nicholas Flay
1. This research was conducted in
conjunction with scientists from the
Groupe de recherche sur la gestion des écosystèmes of Antwerp
University (Belgium) and the Centre Interniversitaire de Recherche
sur le Saumon atlantique (CIRSA) of Laval University (Canada).
Non-native species, river
basin, freshwater fish,
invasion
PRESS OFFICE :
GAËLLE COURCOUX
+33 (0)1 48 03 75 19
[email protected]
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© Leprieur Fabien
Sheet n°290 - March 2008
For further information
DAINA RECHNER
+33 (0)1 48 03 78 99
[email protected]
www.ird.fr/indigo
Percentage of non-native freshwater fish species in 1055 river basins covering more than 80% of the land.
Grégory Fléchet, coordinator
Délégation à l’information et à la communication
Tél. : +33(0)1 48 03 76 07 - fax : +33(0)1 40 36 24 55 - [email protected]