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 each 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.