Environmental Engineering Reference
In-Depth Information
Exports of fi sh fi llet to the EU were valued at € 210 million in 2005 and peaked at
56,000 t of fi llets in 2004, although the fi shery now seems to be declining (FAO
2006) and there are promising signs that many of the endemic cichlids that were
once feared extinct are returning (Witte
et al
. 2000). The future of this fi shery
poses some signifi cant challenges for the three countries that border Lake Victoria
(Tanzania, Uganda, and Kenya) in order to promote both a sustainable commer-
cial fi shery and the conservation of biodiversity (Balirwa
et al
. 2003). The success-
ful reduction in the biomass of Nile perch in Lake Victoria has been possible only
because the fi sh has marketable value. However, many invasive fi sh species may not
have commercial value and the costs of fi shing down the population must be an
ongoing expense on regulatory authorities. This cost must be weighed against the
cost of non-intervention.
13.8.3.2 Common carp in Lakes Crescent and Sorrell, Tasmania
Common carp was discovered in the adjacent and interconnected Lakes Crescent
and Sorrell in Tasmania in 1995. Previous discoveries of carp in Tasmania in the
1970s and 1980s had been eradicated using chemical control (rotenone) but poi-
soning was not pursued in these lakes due to their large size (combined area of
7615 ha) and the consequent cost of a rotenone operation (US$4.8 million in
1998), their value as sports fi sheries, and the presence of an endemic galaxiid.
An integrated control and eradication programme was quickly established based
on physical removal by the Tasmanian Inland Fisheries Service. Objectives of the
carp control programme were fi rstly to contain carp within the Lake Crescent/
Sorrell system, followed by reduction and eventual eradication of carp. A barrier
was constructed to prevent fi sh and larvae from invading downstream of the lakes,
and physical removal has involved netting and electrofi shing, particularly target-
ing spawning aggregations by following groups of radio-tagged male fi sh to locate
spawning sites. Management of water levels in the lakes has been targeted at redu-
cing opportunities for carp spawning (IFS 2004). Recently, exclusion of fi sh from
suitable spawning habitat by the deployment of some 8 km of heavy-duty barrier
netting has further substantially restricted opportunities for carp spawning in Lake
Sorrell. This programme has been successful in substantially reducing the carp
population in both lakes with eventual eradication likely. More than 10,000 carp
have been removed since 1995. Current estimates of the populations of both lakes
are around 100 individuals in Lake Sorrell and 10 in Lake Crescent.
The deliberate or accidental release of non-indigenous fi shes, particularly fresh-
water species, has resulted in signifi cant economic and ecological costs world-
wide, yet our understanding of invasive potential and the development of
effective response tools, especially for large water bodies, lags behind comparable
knowledge for other organisms. However, signifi cant advances have been made
