Data from: Assessing the efficacy and ecology of biocontrol and biomanipulation for managing invasive pest fish

1. Management of non-native species aims to prevent biological invasions
using actions including control and containment of the potential invader.
Biocontrol and biomanipulation strategies are used frequently to reduce
population sizes of non-native species and reduce their ecological impacts
and dispersal rates. 2. Assessments of the efficacy of biocontrol and
biomanipulation actions for managing non-native pest fish, and the
ecological mechanisms involved, were studied here using lentic populations
of the invasive fish Pseudorasbora parva. Biocontrol was through release
of the indigenous piscivorous fish Perca fluviatilis and biomanipulation
through intensive fish removals. 3. A combined biocontrol and removal
programme was completed in an invaded pond over two reproductive seasons.
Almost 10 000 P. parva were removed, with cumulative removal numbers
significantly related to their decreased abundance (>60 to
<0·1 m−2). Ten adult P. fluviatilis were also released initially
and reproduced each season. Analyses revealed P. parva contribution to P.
fluviatilis diet was high initially, but decreased as P. parva abundance
reduced. Individual contributions of the management actions to declined P.
parva abundance were difficult to isolate. 4. The individual effects of
biocontrol and removals on P. parva populations were then tested using a
field trial in replicated pond mesocosms over three reproductive seasons.
Replicates started with 1500 P. parva. The control (no interventions)
revealed no significant temporal changes in P. parva abundances. In the
removal treatment, where over 17 000 P. parva were removed per replicate
over the trial, abundance declined initially, but increased significantly
after each reproductive season as remaining fish compensated through
increased reproductive output. In the biocontrol, abundance declined and
remained low; analyses revealed P. parva were an important dietary
component of larger P. fluviatilis, with predation suppressing
compensatory responses. 5. Synthesis and applications. Biocontrol and
removals can significantly reduce abundances of lentic populations of
small invasive fishes. Removals provide short-term population suppression,
but high effort is needed to overcome compensatory responses. Biocontrol
can provide longer-term suppression but could invoke unintended ecological
consequences via ‘stocking-up’ food webs. Application of these results to
decision-making frameworks should enable managers to make more objective
decisions on risk-commensurate methodologies for controlling small
invasive fishes.