Use of fine‐mesh monofilament gill nets for the removal of rudd(Scardinius erythrophthalmus)from a small lake complex in Waikato, New Zealand

Abstract

Fine-mesh monofilament gill nets were deployed within the three shallow lakes of the Rotopiko complex, Waikato, New Zealand to assess their potential as a tool for controlling or eradicating rudd (Scardinius erythrophthalmus). Nets of different mesh sizes were placed at different spacings and orientations throughout the lakes for two fishing periods, to determine methodology to be used for intensive removal. Rudd were intensively netted for a further two periods and then the success of the operations was assessed. Gill nets of a 13-mm mesh were more effective at capturing rudd when set perpendicular rather than parallel to the shore, whereas there was no significant effect of orientation in 25 mm and 38 mm nets. Comparisons of catch per unit effort (CPUE) on the first night of fishing for M03087; Online publication date 3 August 2004 Received 2 December 2003; accepted 28 April 2004each fishing period showed a significant reduction in the initial CPUE as fishing proceeded. A reduction in the numbers of rudd captured was most marked in the 38 mm nets. 80% of rudd captured over a 7-night period were caught in the first 3 nights of fishing. Post-removal sampling using gill, fyke, and trammel nets, and an electric fishing boat, showed that rudd remained in all of the lakes following intensive removal efforts. However, relative to other methods currently available in New Zealand for control or eradication of unwanted fish, monofilament gill nets appear to be a potentially viable and cost-effective option where ongoing control may provide sustained conservation outcomes.

Managing non-native fish in the environment

“…Although efficacy was limited, with trout <110 mm being less susceptible to capture in the nets and net deployment was effective only in the smaller (shallower) lakes, it at least provided a control method when sensitive, non-target, native species were present that precluded the use of rotenone (Knapp et al 2007). A similar outcome was reported in New Zealand, where gill nets were used to control -but not eradicate -invasive rudd (Scardinius erythrophthalmus, Cyprinidae) in a series of ponds (Neilson et al 2004). An operation to control invasive Eurasian perch (Perca fluviatilis, Percidae) by netting, also in ponds in New Zealand, revealed that timing of the deployment of control methods was important to prevent compensatory responses in the target populations (Ludgate and Closs 2003).…”

Habitat use of non-native burbot in a western river

“…Physical removal of a species attempts to reduce the total abundance, and thus, the recruitment of a species within a system. Suppression of non-native species is fairly common (Neilson et al, 2004;Knapp et al, 2007); however, maintaining a species at low abundance requires consistent removal efforts that can be prohibitively expensive (Quist & Hubert, 2004;Baxter et al, 2007;Gozlan et al, 2010). Therefore, if non-native species are suppressed using physical removal, any effort to increase the efficiency of removal is advisable.…”

Development of a Riverine Index Netting Protocol: Comparisons of Net Orientation, Height, Panel Order, and Line Diameter

“…We did not have sufficient water velocity data to quantitatively determine these covariable relationships. Neilson et al (2004) found that in shallow New Zealand lakes, gill nets with 13-mm mesh were more effective at eradicating rudds Scardinius erythrophthalmus when set perpendicular to the shore than when set parallel to the shore; however, those authors saw no significant effect of net orientation for the 25or 38-mm mesh.…”