New Zealand Journal of Marine and Freshwater Research abstracts
Use of fine-mesh monofilament gill nets for the removal of rudd (Scardinius
erythrophthalmus) from a small lake complex in Waikato, New Zealand
Keri Neilson
Department of Conservation
Science and Research Unit
P.O. Box 112
Hamilton, New Zealand
email: kneilson@doc.govt.nz
Rachel Kelleher
Department of Conservation
Waikato Area Office
P.O. Box 20025
Hamilton, New Zealand
Grant Barnes*
David Speirs
Johlene Kelly
Waikato Regional Council
P.O. Box 4010
Hamilton East, New Zealand
*Present address: Auckland Regional Council,
P.O. Box 92 012, Auckland, 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.
Keywords rudd; Scardinius erythrophthalmus; gill
nets; pest fish control; peat lakes
M03087; Received 2 December 2003; accepted 28 April 2004; Online publication
date 3 August 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
525-539
0028-8330/04/3803-0525 © The Royal Society of New Zealand 2004
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