Darwin Project; Controlling an invasive aquatic plant for improved biodiversity and livelihoods

weed

Project Background
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 (Crocodilus niloticus), Rock Python (Python sebae) and Monitor Lizard (Varanus sp.) 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.

DarwinProjectPast Efforts
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, it came back into the swamp and  re-germinated and was therefore not controlled.

Current Interventions
BirdWatch Zambia (BWZ) was awarded funding to conduct a biocontrol project by the Darwin Initiative of the UK Government for 4 years (2017-2021).

The Darwin Initiative has awarded BirdWatch Zambia (BWZ) funding to conduct a biocontrol project “controlling an invasive aquatic plant for improved biodiversity and livelihoods” in the Lukanga swamps 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 Ministry of Fisheries, Zambia Agriculture Research Institute (ZARI) and Centre for Agriculture and Bioscience International (CABI).

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.

Cyrtobagous salviniae introduced into the Lukanga swamp IBA.

Description

The Cyrtobagous salviniae, also known as the Salvinia beetle, is a natural enemy of Salvinia molesta (Kariba weed), a free-floating fern. The adult Cyrtobagous salviniae (weevils) are small, about 2mm in length and black. Newly emerged adults are light brown on emergence and then turn black (Calder and Sands 1985).

Life Cycle

Adults can live for several months. On Salvinia they are found on or near the growth tips or amongst the roots. Eggs are deposited singly on Salvinia in cavities chewed by the female in unopened buds or amongst roots. Eggs hatch in about 10 days. Females lay 2-5 eggs per day over 60 days. On average the white crescentic larvae complete three instars (stages) in 23 days before pupating in a cocoon. The cocoon is spun beneath the water surface in close contact with or amongst the roots. The prepupae and pupal stage is completed in 10-15 days. The total life cycle, dependent on temperature, is completed in 31-68 days. Dispersal of adults is mostly by the weevils walking or dispersed with their free-floating host plant (Mitchell, 1980).

Feeding Damage

Young larvae feed on the buds (growth tips) and roots while older larvae tunnel into the rhizomes causing leaves to darken and drop off. Adult feeding damages the growth tips and young leaves. Damaged plants become waterlogged and sink. The presence of damaged growth tips is the most characteristic indicator of the presence of the weevils (Forno et al., 1983).

Effect on Salvinia (Salvinia molesta)

Cyrtobagous salviniae is a very effective agent for the control of Salvinia molesta. Weevil damage causes the plants to turn brown and eventually sink and rot. Depending on climate and extent of the Salvinia infestation, mats sink within 1-3 years. Calder and Sands 1985).

More information can be found at; https://www.cabi.org/isc/datasheet/48447, https://www.sciencedirect.com/science/article/pii/S1049964411000673, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0008/425807/Salvinia-biological-control-field-guide.pdf,

Current activities

The weevil, Cyrtobagous salviniae was introduced into the Lukanga swamp on 19th October 2019 at one major habour; Waya- Lyombe. Currently, monitoring activities are underway with an indication of 1.5 m to 3.0 m spread of the weevil from their initial points of introduction. This is evident from the on-going monitoring activities that focus on observing extent of weevil spread, color change of the weed, water- weed ratio in relation to weed control from damage and sinking of the weed.

Weevil monitoring is vital to determine weevil establishment and population increase, to detect spread of the weevil, to assess plant damage, to modify control methods and to provide reports and feedback. The ultimate goal of this weevil monitoring activity by BirdWatch Zambia is  to observe weevil activity in relation to Salvinia molesta control that is intended to improve conditions for waterbirds, other biodiversity and the livelihoods of >2500 fishermen households.

birdwatch_versionCollaborating Technology Partner
MEDEEM Zambia is a social impact organization that specializes in Geographic Information Systems (GIS)and Remote Sensing Image Processing.  Utilizing a decade of Satellite Imagery, MEDEEM developed a situational dynamic GIS application for the project; enabling the project team to perform comparative analysis using satellite imagery.

MEDEEM has a fleet of in-house software solutions for geo-data (GPS/GIS), socio-data and bio-data collection; constantly looking for collaboration opportunities in conservation, wildlife, land management, and industries that require rapid attribute data collection.

Results from Initial Project Mapping Exercise (Satellite Image Analysis)

Project Update

  • November 2018 –Weevil monitoring activities, weevil 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