The Aliens are Here!
by Ron Brown
Ron's web site, about the history of the Merseyside Aquarist Society, is at: http://merseysideaquarist.tripod.com
Aquarticles
Yes, the aliens are here, and have been for quite some time - alien species of fish,
flora and fauna that is!
How is it possible for alien fish, flora and fauna to find their way into our local
marine and inland waterways? Under normal circumstances nature prevents this from
happening because of the vast temperature variations of the seas and oceans and the fishes
natural need for a water temperature of its own liking, fish, and plants, being unable to
cross the temperature barrier.
So, given these natural barriers, how was it possible in Victorian times? Easy, the
Victorians were quite happy to bring alien species to this country for sport, the European
wels catfish (Silurus glanis) being one, which was introduced from Scandinavia.
One was recently caught in West Sussex measuring 5-foot long. The Victorians also over
fished the our native Oyster (Ostrea edulus) to the point of near extinction,
then made matters worse by seeding, in offshore beds, the American Blue-Point Oysters (Crassostrea
virginica). In doing this they unwittingly introduced Slipper Limpets and the marine
snail called the American Oyster Drill (Urosalpinx cinera). The latter feeds on
oysters by drilling a hole through its shell and sucking out the flesh! It doesn't just
eat native Oysters either, eating Mussels the same way if there's nothing else around. The
Slipper Limpet (Crepidula fornicata) was so successful in adapting to our local
waters that, for over 100 years, it prevented local Oysters from re-establishing. However,
with global warming and warmer waters divers are beginning to see a small but significant
increase in their numbers.
The ferocious pike-like predator, the Zander (Stizostedion lucioperca), which
prefers shallow lakes and cloudy lowland rivers, was introduced to the lakes of Woburn
Abbey by the 9th Duke of Bedford in 1878, and since then has spread rapidly, especially
throughout the East Anglian fens.
Rainbow trout (Salmo gairdneri) originate from North America, the first
shipment of eggs being brought to this country in 1884. They are now a quite common and
popular species but are, nevertheless, an alien.
The Victorians can't be blamed for everything though. The Romans brought the Common
carp (Cyprinus carpio) from central Asia. It was probably kept by monks in ponds,
as it was a food fish. Another alien, but nonetheless popular fish, is the Goldfish (Carassius
auratus) introduced into western Europe in the 17th century.
More recently, in 1996 a Dr. Bob Fletcher, a phycologist, or seaweed expert, found Undaria
pinnatifida, a species of seaweed normally found in the ocean seas around Japan, in
the shores of Southampton! How it got there isn't known but it is more than likely that it
spread from French Oyster beds, the weed being accidentally introduced when imported. This
weed is very fertile and will undoubtedly establish itself to the point were it will be
referred to as 'local.' Sargassum muticum is another alien weed that arrived in
the 1970's and is now quite common on the south coast. The indestructible freshwater
oxygenating plant, Twisted Vallis (Vallisneria spiralis), abundant in our rivers,
is another American alien, which was first discovered in the Lea Navigation Canal in 1961.
The American fern, Azolia filiculoides, is now well established in many ditches
as is the Australian rush, Juncus planifolious.
Merchant shipping is another means by which aliens can be introduced. Poisonous
starfish and algae have been transported around the world when shipping takes on ballast
water, later discharging the ballast without a second thought.
Our inland waterways are plagued by alien species; some introduced by quite thoughtless
anglers wanting more and better 'sporting' fish. Some alien fish are so prolific in their
breeding habits that native fishes are all but wiped out. Out of 42 native freshwater
species in Britain almost one quarter are extinct, close to extinction or seriously
endangered, whilst Vendace (Coregonus albula), Powan (Coregonus autumnalis)
and Allis shad (Alosa alosa) are on Schedule V of the 1981 Wildlife &
Countryside Act, which makes it an offence to catch or handle them intentionally. Burbot (Lota
lota) and Houting (Coregonus oxyrinchus) are thought to be extinct. Other
endangered species are, Twaite shad (Alosa fallax rhodanensis), Arctic char (Salvelinus
alpinus), Common sturgeon, Smelt and Schelly.
Another quite aggressive fish is the Pumpkinseed (Lepomis gibbosus), an
American alien, which is, fortunately (so far!), only found in a few lakes in the
southeast of England.
Thoughtless aquarists are another source of danger to native fish when they dump
unwanted fish into local waters, some of which are able to survive. Who would have thought
that a catfish from the Amazon could survive in our local waters? Well it did happen, in
the River Dee in Chester!
Those who are not interested in alien species in our own local waters need only give a
thought to the totally devastating effects cause by the introduction of the non-native
6-foot long monster of a fish, the Nile Perch (Lates niloticus), into Lake
Victoria, which has caused the extinction of many of the endemic Cichlids there.
The Hotties in St. Helens, Merseyside, is another example. Yes, I know they were
tropical fish and that it was warm water coming from Pilkington's Glass factory, but, how
many of the fish dumped there were not tropical species? Not all of them I'll bet. Also,
the wild form of Guppy (Poecilia reticulata) is known to establish itself in some
warm effluents in canals and rivers.
Now global warming is adding to the problem, as more and more fish etc., are able to
cross the natural temperature barrier more easily, bringing with them deadly parasites as
well. Regular alien visits are made by the Almaco Jack (Seriola rivoliana), which
is usually found off the coast of Florida to the Gulf of Mexico. Zebra Sea Bream (Diplodus
cervinus), the first ever to be recorded off the coast of Britain, is native to the
coast of Senegal and Mauritania, northwest Africa. Blue Runner (Caranx crysos)
usually found in the western Mediterranean, throughout the Caribbean Sea and the Gulf of
Mexico, and the Amberjack (Seriola carpenteri) more usually found in the waters
of the Africas and Americas.
It doesn't matter that global warming might not last, it's the damage some of these
vicious and predatory alien fish do to our own native species whilst they're here - they
could quite easily, like the Nile Perch, eat them to extinction! Those that don't get
eaten could easily fall prey to the parasites they pass on.
Yes, the aliens are here!
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