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

Abstract

Summary 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.

Application of environmental DNA analysis to inform invasive fish eradication operations

“…60 by 30 cm crayfish traps with conical funnel entrance and fitted with 5 mm mesh netting). The depletion trapping was complemented by repeated, high density (116 kg ha −1 ) stocking of a native predatory fish, Eurasian perch ( Perca fluviatilis )—a biocontrol method that has been demonstrated to exert a top-down effect on P. parva abundance (Davies and Britton 2015; Verhelst et al 2016). Initial reports received by the authors indicated that by 2014, P. parva were no longer being captured; however, trapping data recently acquired from the venue’s owners revealed persistence of a very small number of P. parva , with the lowest capture densities occurring after predator releases (Fig.…”

Recreational fisheries in the UK: natural capital, ecosystem services, threats, and management

“…The removal of introduced populations is extremely difficult in most rivers and lakes, although some success has been achieved in England in smaller standing waters from which the invasive cyprinid topmouth gudgeon (Pseudorasbora parva) has been successfully removed by the controlled use of rotenone [59,60]. Nevertheless, the best management option is undoubtedly to prevent undesirable introductions from being made in the first place, and to this end all fish introductions to the UK are now subjected to sophisticated risk analyses [61].…”

Monitoring the eradication of the highly invasive topmouth gudgeon (Pseudorasbora parva) using a novel eDNA assay

“…Pseudorasbora parva undergo boom and bust cycles in novel environments, most likely caused by a combination of biotic and abiotic factors, including temperature fluctuations and predation pressure (Britton et al, 2008;Britton et al, 2007). Trapping during low abundance or bust cycles may fail to yield any fish and result in false negatives (Davies & Britton, 2015). eDNA can be a more effective method for assessing presence/absence and could inform the success of eradication measures (Davison et al, 2017).…”

“…In 2014, one pond within the Millennium Coastal Park (Llanelli, South Wales) was reported to have P. parva, despite two previous eradication attempts in 2012 and 2013 (Brazier, 2015). The use of eDNA was recommended as a more sensitive and robust alternative to netting and trapping to test for the presence/absence of P. parva before any further eradication attempts (Davies & Britton, 2015).…”