Pilot Project to Eradicate Invasive Alien Smallmouth Bass



Pilot Project to Eradicate Invasive Alien Smallmouth Bass
Pilot project to eradicate smallmouth bass using a piscicide from the Rondegat River, Cederberg : rationale, river treatments and way forward
Riaan van der Walt
1.Background: The state of freshwater fish of the Western Cape
2.Project location
3.Rondegat River rehabilitation project
4.Thee River mechanical eradication project
5.Way forward
Unique freshwater fishes of the Western Cape
A distinct eco‐region of southern African freshwater fishes
•Low diversity (23 taxa) but high endemicity (19 taxa)
• 4 families but cyprinid dominated, most species small • 16 taxa threatened, (12 Critically Endangered and Endangered)
• Prime threat – invasive alien fishes
• Genetic and morphological studies indicate a richer fauna, especially in the Galaxias (1 species = <10 species)
Four native fish families
Cyprinidae: Barbus (5 species), Labeo (2), Labeobarbus (1), Pseudobarbus (11)
Austroglanididae: Austroglanis (2)
Anabantidae: Sandelia (1?)
Galaxidae: Galaxias (1?)
Extent of alien fish invasion in river systems in the Western Cape
no non‐native species
1‐3 non‐native species
4‐6 non‐native species
7‐9 non‐native species
10‐12 non‐native species
Smallmouth bass
The Rondegat River rehabilitation project
Two primary objectives:
• Reclaiming original distribution range of threatened fish species so as to increase densities and current distribution ranges, thereby down‐listing their conservation status
• Restore natural ecosystem functioning in the designated rivers to benefit the full range of aquatic biota
LEGAL REQUIREMENT: Section 28 of South Africa’s National
Environmental Management Act of 1998 places an obligation
on CapeNature to remedy degradation of environments
The treatment
• Weir constructed at lower end of treatment zone
• Natural barrier 4km upstream is natural barrier bass
• Treatment undertaken with rotenone and supervised by Dr
Brain Finlayson from USA
• Seven drip stations used
• River treated with 1ppm product (50ppb rotenone)
• De-activation station below weir achieved neutralisation at
Potassium permanganate concentration of 2.5%
• First treatment in February 2012 and second treatment in
March 2013.
• 500 bass killed in first treatment and one in second
CapeNature team trained by experts
Drip can station and backpack sprayer
Rhodes Ichthyology students collected about 500 dead bass (17kg biomass) and 90 Clanwilliam yellowfish
Location of the Thee River
Thee River
Native fish species in the Thee River
Cape galaxias - DD
Clanwilliam yellowfish - V
fiery redfin - E
Clanwilliam rock catfish - V
Clanwilliam redfin -V
spotted rock catfish - CE
Thee River mechanical eradication of spotted bass
•4 CapeNature personnel and 6 dedicated volunteers
•gill nets, hand nets (day and night) and electro fishing
•386 spotted bass removed over two summers (2010/2011 and
•No bass found in summer 2012/2013
•Monitor with GoPro cameras and snorkel surveys
Reasons for success
•Low flow in summer
•Clear water
•Spares aquatic vegetation
Way forward
• Expand range of threatened species
• Construction of barriers between main stem and
• Chemical or mechanical eradication above barrier and
bass upper limit
• Focus on tributaries with critically endangered and
endangered species
Many have helped to make this project a Candidate river areas identified for
success. A special thanks to TMF, CAPE and WfW for their support in planning and alien fish control in the Western Cape
executing this project.
Breekkrans River, Cederberg
Biedouw River, Cederberg
[email protected]