Moving forward with rotenone projects: rapid removal of non-native fishes from two farm dams and strong recovery of threatened fishes in a priority river for fish conservation
Dean Impson¹, Riaan van der Walt², Martine Jordaan¹, Jeanne Gouws¹, Sean Marr³ & Olaf Weyl³
¹ CapeNature ² Advanced Environmental Corporation ³ South African Institute for Aquatic Biodiversity and Centre of Excellence for Invasion Biology Unique and Imperiled freshwater fishes of the Cape fynbos region
• Distinct aquatic eco-region of Africa (Cape Fold Ecoregion) • 4 fish families present • 18 of 21 species endemic • Most species small and v. susceptible to alien fish impacts • High number of threatened species and taxa • New species being discovered e.g. giant and Verlorenvlei redfins • Priority area for fish conservation
Cyprinidae – 17 spp dominated by small redfins
Galaxidae – a species complex of likely more than 10 species being described Anabantidae – 1 species?? Austroglanididae – 2 species Major threats, focusing on invasive fish species
• No 1 threat – invasive alien fishes. • Habitat degradation also a major problem • From mid 1850s > 20 species introduced for angling, fish farming and biological control purposes • All major river systems invaded - 21 species • Predatory black basses had most severe impact • Invasive fishes are however backbone of substantial recreational angling and fish farming (trout) industry Extent of alien fish invasion in river systems
no non-native species 1-3 non-native species 4-6 non-native species 7-9 non-native species 10-12 non-native species
Figure: Sean Marr Addressing the threat of invasive alien fishes in five priority rivers in the Cederberg region
Pilot project – Rondegat River
• Rondegat is small Cederberg river with threatened fishes. • It is a national Freshwater Ecosystem Priority River for fish. • Lower 4 km of river invaded by alien smallmouth bass. • Primary goal of CapeNature – eradicate alien fish between weir and waterfall (4km of river) using the piscicide rotenone. • Secondary goal – remove invasive trees from riparian zone • Very supportive riparian land-owner • Two rotenone treatments in 2012 and 2013 removed the bass. • DEA: NRMP funding, Water Research Commission funding. • Biological monitoring led by SAIAB Location of project
Olifants River
Waterfall
Cape Rondegat Town Generally single channel shallow river River
Alien fish
Indigenous fish
Cedarberg Olifants River Wilderness
Area Ongoing strong recovery of threatened endemic fishes in the Rondegat River
1.0
) 0.8
2
0.6
0.4
Density(fish/m 0.2
0.0 2011 2012 2013 2014 2015 2016 2017 Clanwilliam yellowfish Year 0.4
)
2 0.3
0.2
Density(fish/m 0.1
0.0 Fiery redfin 2011 2012 2013 2014 2015 2016 2017 Year
2.0 Control Treatment
)
2 1.5
1.0
Density(fish/m 0.5
0.0 2011 2012 2013 2014 2015 2016 2017 Year Control Treatment Clanwilliam redfin Good recovery of non-target taxa in the Rondegat River
0.4
)
2 0.3 Treatment 2 Treatment 1 0.2
0.1
Density(EPT taxa/cm 0.0 May 10 Mar 11 Jan 12 Nov 12 Oct 13 Aug 14 Jun 15 Year
Control Treatment Cleared riparian zone of alien vegetation Scientific credibility Two dams successfully treated with rotenone in 2017
• Pilot project of two small farm dams in support of registration of CFT Legumine for controlled use • GA’s obtained from DWS • Offstream dam on Krom River invaded with Bluegill sunfish. Dam successfully treated with rotenone by CapeNature on 25 January 2017. • Off-stream dam on Oorlogskloof River, N. Cape invaded by carp. Dam successfully treated with rotenone by CapeNature on 29 March 2017 • Monitoring led by SAIAB, assisted by Freshwater Research Centre, and post graduate students of University of Venda, Fort Hare, Rhodes, Stellenbosch, Zululand and Western Cape • Funding from WRC
Krom River Dam
Aquatic Invertebrates
Phyto- and Zooplankton
Dam near Oorlogskloof River Treatment
Control
• Analysis of aquatic invertebrates, phyto- and zooplankton, rotenone breakdown and water parameters ongoing by researchers Current plans to control of alien fishes in the Fynbos region
• Successful projects will be used to motivate for registration of CFT Legumine for controlled use • Krom River, Cederberg – plan to clear largemouth bass and bluegill in 2017/18 • Biedouw River, Cederberg – plan to clear smallmouth bass and bluegill in 2018/19 • Breekrans River, Cederberg – plan to clear spotted bass in 2019/20
Krom river project
• Focus for 2017/2018 • Hugely supportive land-owners – craft beers named after native fishes • WULA submitted to DWS • Plan is for CN to clear bass and bluegill from river down to natural barrier • Plans tor treatment being prepared – e.g. comms plan, fish disposal plan, treatment plan, rotenone neutralisation plan, site safety and security plan • Biological monitoring has started, led by SAIAB with WRC funding • Plan is to undertake two treatments, 6-12 months apart when river is flowing (October, April) • Native fish introduction plan being prepared in accordance to IUCN guidelines
Map of Krom River
Out: bluegill sunfish
Out: largemouth bass Many thanks for your ongoing support! ACKNOWLEDGEMENTS
Photos / Images: C. Garrow, R. Bills, S. Marr, P. Skelton, O. Weyl, K. Montgomery
Early funders
Best practice guiders
Main funder
Biological monitoring