Controlling an Invasive aquatic plant for improved biodiversity and livelihood on the Lukanga swamp IBA.

weed

The Lukanga Swamp, located 50kms from Kabwe town in central Zambia is recognised as a Ramsar site as well as an Important Bird and Biodiversity Area (IBA) covering approximately 3300 km². It hosts over 350 resident and migratory bird species including some globally threatened species e.g. the Wattled Crane (Bugeranus carunculatus). In addition to avian species this site also holds a good population of semi-aquatic antelopes such as Sitatunga (Tragelaphus spekei), Oribi (Ourebia ourebi) and a few Red Lechwe (Kobus leche leche). Reptiles such as the Nile crocodile, Rock Python and Monitor Lizard are also common in isolated portions of the swamp. The Swamp is highly important for the fishing local community, with its small islands, and the surrounding mainland, hosting approximately 22500 fishing community members which translates to at least 2500 households whose livelihoods are supported by fishing from the swamp. This swamp supports about 20% of Zambia’s fish.

Unfortunately, since 2009 the swamp has been infested by the invasive Kariba weed (Salvinia molesta) which currently covers about 2000 km² (>60% surface area) of the swamp. Since then, records from the Department of Fisheries, local councils and interviews with local resident fishermen have indicated reduced catch per effort (from ca. 35kg/hr to >20kg/hr) and most of the fish has moved further into the swamps, in areas not infested by the Kariba weed. This has led fishermen to use more gear and in some cases use incorrect fishing gear such as Mosquito nets and poisons to catch more fish. The weed forms a mat on water, reducing both sunlight and oxygen underneath which ultimately may lead to death of fish.

BirdWatch Zambia (BWZ) in 2013, attempted a manual control of the Salvinia molesta where the community members where involved by using hands and rakes to remove the weed from the swamp. This method proved futile as the weed was difficult to clear hence it re-germinated and was not controlled.

Through BirdLife International, BWZ was awarded funding to conduct a biocontrol project by the Darwin Initiative of the UK Government for a 4 years project (2017-2021).

The Darwin Initiative awarded BirdWatch Zambia (BWZ) funding to conduct a biocontrol project “controlling an invasive aquatic plant for improved biodiversity and livelihoods” in the Lukanga swamp Important Bird and Biodiversity Area (IBA). This project will control the weed by introducing a very effective and host specific weevil, Cyrtobagous salviniae. Weevil damage causes the plants to turn brown and eventually sink and rot. Depending on climate and extent of Salvinia infestation, mats sink within 1-3 years. This multi-year project seeks to control the weed by introducing a weevil, Cyrtobagous salviniae, a known natural enemy that exclusively feeds on the Kariba weed. This is expected to improve habitat conditions for waterbirds, other biodiversity as well as the livelihoods of >2500 fishermen households.

This project is being conducted in partnership with the Department of Fisheries, Zambia Agriculture Research Institute (ZARI) and Centre for Agriculture and Bioscience International (CABI), Zambia Environmental Management Agency (ZEMA) and several other partners.

Once the weed has been controlled, the following is expected; improved fish catch, restored habitat, increased dissolved oxygen in water and an increase in the population of the globally threatened species and other waterbirds. The prime objective of the project is to improve conditions for waterbirds, other biodiversity and the livelihoods of >2500 fishermen households.

CURRENT ACTIVITIES

At the moment over 2000 adult weevils have been introduced on the swamp at 33 points and at least 11 points have merged. An average distance of approximately 34m is covered by the weevils monthly with a maximum distance of 2400m from one release point since initial introduction in October 2018. Weevils have covered an approximate area of 662km² which is approximately 20% of the infested area of the swamp. These results are obtained from site monitoring activities that are focused on observing the extent of spread of the weevil spread, the browning score of the Salvinia and as well as recording any effect of the weevil on associated plants.

Additionally, eight control points (Non-weevil release sites) have been selected and georeferenced for comparison with the weevil release sites. At present, one control point has merged with a release point, symbolizing a great extent of weevil spread.

Weevil mass rearing has been up scaled. We currently have increased mass rearing avenues 13 mass rearing avenues from the initial 6 at the start of the project.  In 2019, we experienced some weevil mortalities in one mass rearing facility due to unapplied proper mass rearing guidelines by weevil monitors on site. This has been mitigated by providing a refresher mass rearing course to parties involved. Mass rearing is done so as to increase the weevil population prior to introduction into additional points in the swamp.

Cyrtobagous salviniae performs better in a temperature range of between 25.5°C and 33.5°C with a good supply of fresh green Salvinia molesta. In an effort to maintain the water temperature at optimum in the mass rearing troughs, the project team has employed the use of warm water, heated by floating water heating elements. Waterproof thermometers are used to ensure that water temperature is optimum. At optimum temperatures (25.5°C to 33.5°C), the feeding and breeding rate of the weevils is at its peak thus increasing chances of reproduction and ultimately Salvinia molesta control.

Additionally, the use of a water soluble nitrogen-rich fertilizer promotes the speedy development of Salvinia molesta growth tips and improves nutrition in the water that supports the development of the larvae, pupa and egg life cycle stages.  The fertilizer improves the health and growth rate of Salvinia molesta which ultimately produces lots of healthy weevils as a result of an improved food supply. In addition to that, nitrogen is known to increase the size of females thus leading to large egg clutches.

Awareness raising to stakeholders and the local community remains a vital aspect of this project. The target groups are the fishermen, traders, pupils and traditional leaders and relevant stakeholders. At present, a total of 3104 individuals, comprising 1799 (58%) males and 1305 (42%) females have been reached. These talks are centered on discussing the project intervention, how the weevil works, as well as the Dos and Don’ts with regards to good weevil management to improve the rate of success. These are usually interactive talks with visual awareness raising materials such as posters, a banner, invasive species guide and weevil life cycle leaflets.

PROJECT UPDATE TIMELINE

  • March 2020 – Weevil nurturing, World Wetlands Day Commemorations
  • February 2020 — Gillnet Survey in Chiyuni
  • January 2020 — 6th Project Steering Committee Meeting
  • December 2019 – – Gillnet Survey in Waya
  • November 2019 – Weevil monitoring in Chilwa and Chiyuni, awareness raising in Chiyuni and at LIUTEBM University, weevil introduction in Chilwa
  • October 2019 – Weevil monitoring in Waya, Radio appearance, 5th Project Steering Committee meeting
  • September 2019 –Pond nurturing and maintenance in Waya, Impact/Extent Survey, Mass rearing at Chilanga fisheries, Enhanced mass rearing techniques.
  • August 2019- Pond nurturing and monitoring Waya, trough monitoring activities in all sites
  • July 2019 – Trough monitoring Activities, 4th Project Steering Committee Meeting,
  • June 2019 – Biodiversity Survey in Lukanga.
  • May 2019 – Weevil monitoring activities, introduction of weevils in Chilwa, awareness raising talks, trough monitoring.
  • April 2019- Weevil introduction in Chilwa and Waya, awareness raising in Chilwa and Waya.
  • March 2019 – Quarterly Project Steering Committee meeting, invasive species talk at Rusangu University, Participation at the invasive species symposium in Gaborone, Botswana.
  • February 2019 – Weevil monitoring activities, awareness raising talks, pond managers training, weevil introduction into troughs in Chilwa and in pond 2 in Waya.
  • January 2019 – Construction works on Pond 2, completion of weevil Introduction and weevil monitoring reports.
  • December 2018 – Weevil introduction into Pond 1, Weevil monitoring activities.
  • November 2018 –Weevil monitoring activities, weevil mass rearing pond construction, steering committee meeting and site visit.
  • October 2018 – Weevil shipment received, Weevil introduction
  • September 2018 – Pond management training, Selection of weevil introduction sites
  • August 2018 – Weevil importation procedures
  • July 2018 – EPB approved
  • June 2018 – ZEMA site inspection, Post baseline survey
  • May 2018 – Courtesy call on traditional leaders
  • April 2018 – Submission of final EPB report
  • March 2018- Inception meeting for Monitoring and Evaluation Steering Committee.
  • February 2018- Traditional leaders courtesy call
  • January 2018- Zambia Environmental Management Agency (ZEMA) report reviews
  • December 2017- Environmental Project Brief (EPB) activities
  • November 2017- Baseline survey
  • October 2017- Project inception meeting

Satellite image analysis of Salvinia molesta infestation