Alien/exotic, indigenous, endemic and translocated?:
These terms are often confused by both scientists and non-scientists. But if the
terms are well defined so that they can be understood by everyone. These
universal terms can be used effectively and without confusion anywhere in the
world. The definitions should not be limited by local political boundary usage
as done by some scientists.
Alien/exotic:
Why two
terms if they mean the same thing? De Moor and Bruton (1988) defined alien
species as one that was " an introduced species from outside of the
boundaries of southern Africa." This definition is misleading and denotes a
political boundary and not the correct natural range of the species. We should
consistently now use alien for any fish species which has been moved outside of
it's natural known home-range. The term exotic and using political boundaries in
the definition should not be used.
Indigenous: The
public, and even some scientists, are confused with the correct useage of
indigenous. Within South Africa ‘indigenous' has been freely used to mean
South African fish species as compared to alien fish species, such as bass and
trout, which were introduced from other countries. Indigenous species can be
defined as one which occurs naturally in the locality it is found, that is it's
natural home-range. The sharptooth catfish (Clarias gariepinus ) is indigenous
to many rivers from the Nile to the Orange River but once it moved along the
Orange-Fish tunnel to the Great Fish River it became an alien fish species in
the Fish River.
Translocated: De Moor
and Bruton (1988:2) defined ‘translocated indigenous species' as " a
species naturally found within southern Africa but which has been translocated
either intentionally or unintentionally by man into catchments in which it was
not naturally distributed." It is unfortunate that they introduced this
terminology which is misleading and unnecessary. By definition these ‘translocated
indigenous species' are alien species. Translocated should only be used to
denote how the fish species got to where it is now. If it has been translocated
by anglers, engineers or in any way by man outside of its natural range it thus
becomes an alien species. As noted above the sharptooth catfish became an alien
species when engineers connected the Orange and Fish rivers via a tunnel and the
catfish could now translocate themselves to the Great Fish River.
Endemic: There may be some
confusion between the terms endemic and indigenous. When does an indigenous fish
species become an endemic species? Endemic is a bit of a vague term and usually
means that the species in question occurs naturally in a particular place only
and the term should be used for species with a restricted range. But what does
restricted range actually mean? It refers to a species that is restricted in its
distribution to a particular lake, drainage system or biogeographical region.
For example, some of the endemic species in the Olifants River system of the
Western Cape, such as the magnificent Clanwilliam yellowfish (Barbus capensis),
occur only in that system and as such are endemic to it. However, some species
will be endemic to only small sections of this river system and should not be
moved out of their natural ‘endemic range' within the system as happened with
the Clanwilliam yellowfish.
It is thus important that these terms are used correctly so everyone will be
able to understand what scientists are saying. The sharptooth catfish (Clarias
gariepinus) is indigenous to the Orange River but is not endemic to the Orange
River as it also naturally occurs widely throughout Africa. It becomes an alien
only when it has been moved out of it's natural range, such as into the Great
Fish River. Therefore bass (from North America), rainbow trout ( from North
America) and C. gariepinus (from Africa but from rivers from the Orange to the
Nile) would all be alien species in the Olifants River in the Western Cape.
Who are the alien fish introduction culprits?
The people responsible for introducing alien fish species cover a wide range
from aquaculture scientists in universities, government conservation officials
(strange eh!), engineers, aquaculture enterprises, farmers, recreational
anglers to the little boy emptying his fish tank into the river.
How engineers do it:
Engineers connected the Orange River to the Great Fish River via an 82km long
tunnel. This Orange-Fish tunnel is what many dubbed an engineering feat but it
was an environmental disaster. This artificial connection between two previously
separate river basins is called an ‘Interbasin Transfer' of water. Not only
did this tunnel transfer the muddy Orange River water with it's particular
chemistry to the Great Fish River, it also changed the flow regime of the Great
Fish River and of course fish species from the Orange River got a free ride to
the Great Fish River. It is even possible that some species from the Great Fish
River, like freshwater eels, may make it through the tunnel to the Orange River.
These eels would have normally matured in the Great Fish River and then after
10-20 years in freshwater they would swim to the Indian Ocean and up the coast
to Madagascar to spawn. When they now swim down the Orange River they will
probably swim to their death as the currents that they evolved with on the east
coast of Africa will not be there! All the interbasin transfers in South Africa
are potential ecological disasters. The engineers should consider ways to
prevent these alien introductions.
Inlet
tower of the Orange- Fish tunnel in the Gariep dam, an expensive alien fish
conduit.
Conservation officials:
Some people apply different rules to aquatic ecosystems compared to terrestrial
ecosystems. Many conservation departments in South Africa have a history of
alien fish propagation and dispersal. With all we now know of alien fish impacts
on aquatic biodiversity it is truly amazing that some conservation organisations
still rear and introduce alien fish. Would they consider introducing alien
mammal species into the terrestrial ecosystems, eg tigers into Kruger Park?.
Recreational anglers:
Recreational anglers who are responsible for alien fish introductions fall
within two camps, the informed and the ill-informed. For the ill-informed it is
necessary to get the message out about alien fish impacts. For the informed
there must be legislation, large fines and vehicle confiscations. Anglers who
take the movement of fish into their own hands are breaking the law but they are
also potentially ruining existing sport fisheries. It is ironic that in the
Western Cape anglers have recently introduced sharptooth catfish into a premier
alien bass fishing venue. So in the past the introduced alien bass ruined this
venue as one for angling for indigenous species and today alien catfish
introductions are ruining the venue for alien bass fishing. This is a clear
message to all anglers that the legislation on moving live fish exists for good
reasons.
Alien alert - Yellowfish angling:
In South Africa we have a number of yellowfish species which are excellent
candidates for recreational angling. A group of conservation officials are
popularising fishing for indigenous species rather than alien bass and trout.
However, there is an alien alert warning on this project as conservation
managers and anglers may start moving the yellowfish from one system to the
next. This will of course make them aliens. What is even worse the introduced
yellowfish may hybridise with the indigenous yellowfish in the system. This
means we may loose yellowfish species. Also if hatcheries are rearing hundreds
of thousands of yellowfish and introducing them around the country then we have
a potential major problem on our hands. Dumping thousands of juvenile yellowfish
into a river which were artificially spawned from one or two males and females
in a hatchery can also cause genetic problems to the naturally spawned
yellowfish populations in a system as well as introducing parasites and diseases.
So caution is needed. Strictly controlled, catch and release of the naturally
spawned yellowfish, may be the way to go on this issue. Education will play an
important role.
Farmers:
The farming ‘my stretch of river' attitude of some farmers can lead to alien
fish being introduced into river systems. Alien fish are a form of ‘bio-pollution.'
If the alien fish survive and breed then the farmer is responsible for long-term
and possible irreversible impacts to the river ecosystem not just on his farm
but as far as the alien fish can penetrate within the system. Even off-stream
farm dams are a problem. If the dam wall breaks the fish can get into the river
or when the dam overflows the fish can move.
How you can help stop eco-terrorism! Become alien aware.
Promote ‘River Health' by preventing bio-pollution to our rivers. Make people
aware by relating to them items in this article or a previous SiA article on
alien trout
or ask them to read the Albany Museum's Makana Biodiversity Centre's
website on
alien fish species.
People who
illegally introduce fish into river systems and dams are eco-terrorists.
Eco-terrorist activities as with all terrorist activities need to be stopped, we
can all help.
References:
DE MOOR I and BRUTON MN (1988) Atlas of alien and translocated indigenous
aquatic animals in southern Africa. South African National Scientific Programmes
Report No. 144: 1-310. CSIR, Pretoria.
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Contact Dr Jim Cambray at j.cambray@ru.ac.za
