After Bolander approached CapeNature on possible practical solutions to curb the killing of thousands of frogs during migration or dispersal on the R44 in Somerset West, (“Frogs killed in attempts to cross a busy road in Somerset West”, Bolander February 19, 2024) Petro van Rhyn, spokesperson for CapeNature responded with alternatives to look into.
According to Ms van Rhyn the frogs in question seem to be (based on footage viewed of the mass movement) of the Common Platannas and/or Clicking Stream Frogs.
“The Common Platanna is a very abundant frog listed as ‘Least Concern’ that has adapted well to human-altered habitats, utilise human water infrastructure and thrive in urban/peri-urban environments.
“The mass movements are typically driven by the drying up or shrinkage of the source water body thus creating an excessive concentration of frogs and overland movements are normally very quick,” she says.
In urban areas where there are busy roads, she says this type of carnage are expected during mass movements.
In answer to Bolander last week, Eddie Andrews, Deputy mayor and mayoral committee member for spatial planning and environment, suggested the building of an underpass through which the frogs could move over the R44.
This is a recommendation included in proposed suggestions by CapeNature. “Normally the recommended mitigation is to construct underpasses to direct animal movement under roads as they have done in a couple of places in the City of Cape Town for the Endangered Western Leopard Toad, which moves from water bodies for breeding, back to the terrestrial areas they inhabit for the rest of the year,” Ms Van Rhyn suggests.
Frog Friends Helderberg in their previous responses recommended the building of a wall as a temporary solution to prevent the frogs from crossing at the current point and redirect them further down the path to the tunnel located further down along the same stretch of road.
CapeNature adds to its suggestions the construction of barriers on the Paardevlei side as a preventative measure to stop the frogs getting to the R44, but although this can be considered as an alternative solution, there is no guarantee that the frogs will not die on the other side of the barrier, “but this may be a more natural situation than the road crossing,” states Ms Van Rhyn.
Another one of Mr Andrews’ suggestions was to alternatively create a waterbody on the side of the Paardevlei dam, so as to eliminate the need for the frogs to migrate to the waterbody on the other side of the road.
But, Ms Van Rhyn says this may not be effective in stopping the mass movements. “Constructing additional wetlands on the barrier side may also not necessarily resolve the incidence of future mass migrations as the additional wetlands will likely lead to larger Common Platanna population numbers,” she explains.
She points out the installation of barriers on the Paardevlei side, preventing the frogs from crossing the R44 as the most practical solution.
