Grass carp Effectiveness and Effects Stage 2: Knowledge review Prepared for the Department of Conservation May 2014 DISCLAIMER: The Department of Conservation takes no responsibility for the accuracy of this report and the findings and opinions expressed therein. The opinions and recommendations expressed are those of the contractor and may not reflect Department of Conservation policy and practice. Authors/Contributors : Dr DE Hofstra For any information regarding this report please contact: Dr DE Hofstra Scientist Aquatic Plants +64-7-859 1812 [email protected] National Institute of Water & Atmospheric Research Ltd Gate 10, Silverdale Road Hillcrest, Hamilton 3216 PO Box 11115, Hillcrest Hamilton 3251 New Zealand Phone +64-7-856 7026 Fax +64-7-856 0151 NIWA Client Report No: HAM2014-060 Report date: May 2014 NIWA Project: DOC13214 © All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). 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Contents Executive summary ..................................................................................................... 4 1 Introduction ........................................................................................................ 6 1.1 Grass carp .................................................................................................. 6 1.2 Scope, Stage Two – knowledge review ....................................................... 8 2 Approach ............................................................................................................ 9 3 Lakes ................................................................................................................. 10 3.1 Northland lakes ......................................................................................... 10 3.2 Auckland Region – rural lakes ................................................................... 37 3.3 Auckland Region – urban or man-made ponds ......................................... 51 3.4 Waikato ..................................................................................................... 67 3.5 Hawke’s Bay ............................................................................................. 67 3.6 Taranaki .................................................................................................... 92 3.7 Wellington Region ..................................................................................... 96 3.8 Canterbury .............................................................................................. 100 4 Discussion ...................................................................................................... 103 4.1 Effectiveness ........................................................................................... 103 4.2 Effects ..................................................................................................... 106 5 Summary and Recommendations ................................................................. 109 6 Acknowledgements ........................................................................................ 111 7 References ...................................................................................................... 112 Appendix A List of potential field sites from DOC ..................................... 134 Appendix B Short-list of lakes .................................................................... 135 Appendix C Location of lakes and ponds .................................................. 136 Reviewed by Approved for release by Dr Dave Rowe Dr John Clayton Formatting checked by Grass carp Effectiveness and Effects Executive summary Department of Conservation (DOC) contracted NIWA to prepare a report that collated the existing knowledge on the effectiveness and effects of using grass carp ( Ctenopharyngodon idella ) for weed control in New Zealand, drawing on published, unpublished and other information for the lakes of interest. The information was used to review the effectiveness of grass carp in terms of the weed control and/or eradication outcomes for which they were stocked and the effects of the grass carp on water quality, habitat quality and flora and fauna at the transfer locations. Grass carp are a species of herbivorous fish that were introduced to New Zealand for aquatic weed control. Grass carp have been deployed for weed control in a wide range of locations in New Zealand including lakes, ponds, drains and stormwater retention systems. DOC have a statutory role in the approval of grass carp release to a new location (where grass carp do not already exist). However DOC consider that insufficient information is available regarding the effects of grass carp on the ecosystems that they have been transferred into. The purpose of this review of the effects and effectiveness of grass carp is to improve future decision making. A total of 24 lakes and ponds were selected by DOC. Information for those waterbodies was sourced primarily from NIWA, DOC, MPI (Ministry for Primary Industries) and regional councils. Amongst the sites, grass carp had not been released into two of the lakes, nine were natural lakes and fifteen were man-made lakes, the majority of which are used for storm water retention. NIWA visited 15 of the sites within the summer to early autumn field season (2013/2014) and updated the vegetation records. Although some significant data sets on vegetation and water quality were readily available, there were information gaps in other aspects of the lake ecology, such as adequate pre- release baseline information, actual grass carp stocking density, and post-stocking monitoring. Information, and lake records were generally more complete for natural lakes, and recent stocking events (i.e., within the last six years). Grass carp can be effective weed control agents for submerged aquatic plants. Total removal of all submerged vegetation is normally the long-term outcome, and partial weed control is rarely achieved. Grass carp are preferential browsers of plants, consuming both target and non-target species in order of their relative palatability and their accessibility to the grass carp. Impacts on non-target plant species, effects on fauna, water and habitat quality were reported for some sites and were largely dependent on waterbody characteristics. In making recommendations for future decision making it was recognised that DOC only approves releases to new locations (MPI approves subsequent releases), and that DOC procedures already reflect some aspects of the recommendations. It is recommended that; 1. Assessment of an application to release grass carp, takes in to account the ecological functions, the weed issues, and the appropriateness of using grass carp in the waterbody. 2. Applications are assessed on the basis that there will be complete removal of submerged aquatic plants. Grass carp Effectiveness and Effects 4 3. The approval includes (i) the grass carp stocking density and containment measures, (ii) monitoring requirements for the aquatic plants, (iii) environmental monitoring that aligns with the risks and consequences of adverse effects to that waterbody, and (iv) submission of monitoring reports to DOC and MPI (ideally in a centralised repository, see point 4). 4. Environmental impact assessments, applications for stocking grass carp, actual stocking records, and monitoring reports are supplied and maintained, through a centralised system with DOC and MPI so that information can be readily tracked for waterbodies and catchments. Grass carp Effectiveness and Effects 5 1 Introduction 1.1 Grass carp Grass carp ( Ctenopharyngodon idella ) are a herbivorous fish, native to Asia, that derive their other common name, white amur, from the Amur River system that borders China and Russia (Cudmore and Mandrak 2004). They have been introduced to New Zealand and many other countries for aquatic weed control. The first consignments of grass carp arrived in New Zealand in 1966 (Chapman & Coffey 1971), and again in 1971 (Edwards & Hine 1974) with initial studies focussed on feeding preferences (Edwards 1973, 1974). Grass carp were subsequently released for a variety of field studies in small lakes to assess their potential impacts, such as Parkinsons and the Waihi Beach reservoir (Mitchell 1980, Rowe 1984) and drainage systems on the Rangitaiki Plain (Edwards & Moore 1975) and the Mangawhero Stream (Schipper 1983) in the Waikato. These initial studies provided data on the potential use of grass carp for weed control in temperate New Zealand environments and addressed the potential impacts of grass carp in lakes (Rowe and Hill 1989). Issues with respect to containment arose after fish escaped into the Waikato River (McDowall 1984), and this event resulted in the production of an Environmental Impact Assessment to formally address the use of this fish for weed control in New Zealand (Rowe & Schipper 1985). The report analysed the