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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., 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., 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., 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., 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. [ABSTRACT FROM AUTHOR]

ABSTRACT Accidental introductions of non-native species into aquatic environments often result in invasive populations that cause substantial conservation concerns. They account for 8% of all fish introductions and often occur when fish consignments are intentionally released into the wild ('stocked') but are unknowingly contaminated with a 'hitch-hiking' species that is also released., This study tested the efficacy of a fish stocking audit procedure in preventing the introduction of a model hitch-hiking fish ( Pseudorasbora parva) within a batch of model native fish ( Rutilus rutilus). It was tested in relation to different P. parva contamination levels (1, 5, 10, 20%), auditor expertise (Expert, Intermediate, Novice) and search effort., There was considerable variability in the detection thresholds among contamination levels, auditor experience and search effort; false-negative recordings reduced as all these parameters increased. Probability of P. parva detection (POD, 0 to 1) showed that at the lowest search effort, POD was greater than 0.80 for Expert auditors only when contamination levels exceeded 10%. At the highest search effort, POD was greater than 0.80 at the 1% contamination level for Experts, but was at 3 and 8% contamination for Intermediates and Novices., Thus, while small non-native fishes are at risk of being accidentally introduced owing to their difficulty of detection in stocking consignments, an effective audit procedure using experienced auditors and high search effort reduces this risk. Implementation should help prevent subsequent invasions, protecting native species from their adverse ecological consequences., Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]