30 – Recovery of the red-finned blue-eye^379although vigilance is required to maintain stock exclusion and to monitor for, and
control, pigs.
The continued existence of red-finned blue-eye at Edgbaston relies on
maintaining the species in gambusia-free springs. This is fraught with difficulty
due to the colonising ability of gambusia, the f lat landscape and the
unpredictability of high rainfall events that facilitate gambusia movement. In
response, Bush Heritage, in consultation with the Red-finned Blue-eye Recovery
Team, has implemented several management interventions.
Quarantine extant red-finned blue-eye populations through barrier fencing
Barrier fencing has been erected around occupied springs as an emergency
intervention to protect extant red-finned blue-eye populations. Fences are
constructed from a mesh that allows movement of water and fine particulate
matter but precludes fish movement, thereby preventing gambusia colonising new
springs or migrating out of infested springs. Fences are laborious to construct and
require regular maintenance but appear to be effective: after 2 years, gambusia had
not colonised four of five fenced springs (Kerezsy 2015), with gambusia infestation
only occurring when the fence was damaged or degraded. More durable barrier
fencing material has been developed recently to increase effectiveness and reduce
replacement frequency and therefore overall costs.
Removal of gambusia from infested springs
A key objective of the Red-finned Blue-eye Recovery Program is to increase the
number of populations (i.e. occupied springs) at Edgbaston. Given red-finned
blue-eye already occupy virtually all gambusia-free springs, this can only be
achieved in two ways: (1) eradicating gambusia from infested springs; or (2)
creating new (artificial) spring habitat.
Two methods of gambusia removal have been trialled. Physical removal
involved partitioning springs and using nets to remove gambusia. Although this
method minimised potential harm to non-target organisms, it was impractical for
all but the smallest springs. Removing fewer than 500 gambusia from a small
spring (<3 m^2 ) required multiple visits at different times of the day over 6 months
(Kerezsy 2009).
Chemical eradication of gambusia using the fish poison rotenone was trialled
in 2011–2012. Trials examined both the concentration and rate of application
required to eradicate gambusia from springs, and the sensitivity and resilience of
the threatened invertebrate spring community to rotenone. The trials
demonstrated that gambusia removal was feasible with multiple applications and
the aquatic macroinvertebrate community was not adversely impacted (Kerezsy
and Fensham 2013). To date, gambusia have only been removed from one spring
but rotenone provides a plausible means to recover habitat and render some springs
suitable for red-finned blue-eye reintroduction.