Environmental Engineering Reference
In-Depth Information
may provide refuge for fi sh in untreated pockets of water (Rayner and Creese
2006). Ground water recharge and subsurface springs also compromise eradica-
tion attempts. Generally, eradication is most successful in small, easily accessible,
closed, shallow, lentic water bodies that are sparsely vegetated.
Chemical eradication of non-indigenous fi sh from fl owing waters presents
special di
culties. Dewatering the system by diverting stream fl ow or treating
during low fl ow periods may create disconnected pools that need to be identi-
fi ed and treated separately. All other possible refugia such as minor tributaries
must also be separately treated, and the reinvasion of fi sh from downstream
must be prevented by constructing physical barriers or relying on natural barr-
iers such as waterfalls. h is approach has been successful in eradicating rainbow
trout and brown trout in Australia to restore small streams for indigenous gal-
axiids. However, a high level of invertebrate mortality may result from rotenone
treatment (Lintermans and Raadick 2003) and the ultimate success of these
treatments may be compromised by subsequent illegal restocking of salmonids
(Rayner and Creese 2006).
h e two key variables aff ecting the response of fi sh to toxicants is concentration
and contact time. Applications need to ensure complete mixing and adequate con-
tact time which may be di cult to achieve in fl owing waters. h e toxicity of all fi sh
control chemicals is markedly aff ected by environmental conditions such as water
temperature, dissolved oxygen, hardness, pH, particulate organic matter, salinity,
light exposure, substrate and plant adsorption. Sensitivity among fi sh species also
varies greatly with salmonids typically more sensitive than coarse fi sh such as carps
and catfi sh. Juvenile stages are usually more sensitive than adult, probably due to
greater relative surface area for uptake and greater mass specifi c metabolic rate.
However, fi sh eggs are usually less sensitive to the common piscicides than larvae,
juveniles, and adults. For example, salmonid eggs are around 100 times less sensi-
tive to rotenone than juveniles or adults so eradication eff orts should be timed for
post-hatch or pre-spawning (Ling 2003).
A signifi cant disadvantage of chemical renovation of natural water bodies is
the likely signifi cant or total loss of non-target fi sh species. h ese then need to be
reintroduced if a suitable source population is available and if su cient numbers
can be released to re-establish the species.
Rotenone
Rotenone, either in liquid or powdered formulations, has been used for many
years primarily for the elimination of unwanted fi sh from enclosed static water
bodies, but has also been used to poison fl owing waters (streams and small riv-
ers). The use of rotenone for fi sheries management has been extensively reviewed
in recent years (Finlayson
et al
. 2000; Ling 2003; Rayner and Creese 2006). The
largest user of rotenone for fi sh control is the USA (roughly 5.5 t per annum)
and usage is equally divided between powdered and liquid formulations (McClay
2002). Powders are now often favoured for the treatment of static waters because
of their signifi cantly lower cost, while liquid formulations are favoured for fl owing
