hybrids of X. laevis and X. gilli are listed as requiring control (Category 1b), and
S. gutturalis is listed as requiring control (Category 1b in the Western Cape) under
the Alien and Invasive Species Regulations (RSA 2016).
22.6.1 Sclerophrys gutturalis (Guttural Toad)
Sclerophrys gutturalis was first observed in the Western Cape in 2000 (De Villiers
2006), more than 1200 km from the native population to the north in Durban
(Telford et al. 2019; Measey et al. 2020, Chap. 5). Environmental managers are
concerned about this invasion because of the co-occurrence of endemic Endangered
(IUCN 2017) Sclerophrys pantherina (Western Leopard Toad) in the same area.
Guttural Toads have been subject to control operations in the City of Cape Town
since 2010. The aim of the programme is to extirpate the species in the City and
prevent its re-introduction. The City of Cape Town’s Invasive Species Unit has
contracted a private firm to locate and remove toads at a cost of approximately ZAR
200,000 per annum. The firm works closely with municipal staff to visit land
owners, undertake nocturnal searches and remove toads from private property and
green areas. All life stages were targeted for removal until demographic modelling
revealed that removal of eggs and tadpoles had very little impact on population
numbers and that effort was best expended on removing juvenile and adult toads
(Vimercati et al. 2017a). During the 8 years of the control operation, the invaded area
has increased from a few properties in one suburb to occupy about 5 km
2 in 2009 and
over 8 km
2 by 2015 (Measey et al. 2017). Records of toads in outlying suburbs on
the southern side of the Cape Peninsula mountain chain have raised concern that
human-mediated jump dispersal could significantly increase the invaded area
although such populations have not yet established.
Bureaucratic delays also impact negatively on the project’s effectiveness. Each
year, a new contract has to be issued and delays in the contract process and the
availability of funds can cause delays of several months after the start of the breeding
season in October/November. In most years, management only commences in
December or January, providing ample opportunities for the toad population to
increase and occupy new ponds in the first part of the breeding season. Gaining
access to numerous private properties in this high-income, low density, housing area
has been a major impediment to control, with models suggesting that missing 55% of
properties undermines the total management effort with no net effect (Vimercati
et al. 2017b; Potgieter et al. 2020, Chap. 11). The Guttural Toad management effort
has been sustained until the present, but based on the recent data researchers and
managers have discussed the possibility of changing the aim of the control operation
from extirpation to containment, because without increased effort and dedicated
long-term funding, it is unlikely that extirpation will be achieved.
646
S. J. Davies et al.
S. gutturalis is listed as requiring control (Category 1b in the Western Cape) under
the Alien and Invasive Species Regulations (RSA 2016).
22.6.1 Sclerophrys gutturalis (Guttural Toad)
Sclerophrys gutturalis was first observed in the Western Cape in 2000 (De Villiers
2006), more than 1200 km from the native population to the north in Durban
(Telford et al. 2019; Measey et al. 2020, Chap. 5). Environmental managers are
concerned about this invasion because of the co-occurrence of endemic Endangered
(IUCN 2017) Sclerophrys pantherina (Western Leopard Toad) in the same area.
Guttural Toads have been subject to control operations in the City of Cape Town
since 2010. The aim of the programme is to extirpate the species in the City and
prevent its re-introduction. The City of Cape Town’s Invasive Species Unit has
contracted a private firm to locate and remove toads at a cost of approximately ZAR
200,000 per annum. The firm works closely with municipal staff to visit land
owners, undertake nocturnal searches and remove toads from private property and
green areas. All life stages were targeted for removal until demographic modelling
revealed that removal of eggs and tadpoles had very little impact on population
numbers and that effort was best expended on removing juvenile and adult toads
(Vimercati et al. 2017a). During the 8 years of the control operation, the invaded area
has increased from a few properties in one suburb to occupy about 5 km
2 in 2009 and
over 8 km
2 by 2015 (Measey et al. 2017). Records of toads in outlying suburbs on
the southern side of the Cape Peninsula mountain chain have raised concern that
human-mediated jump dispersal could significantly increase the invaded area
although such populations have not yet established.
Bureaucratic delays also impact negatively on the project’s effectiveness. Each
year, a new contract has to be issued and delays in the contract process and the
availability of funds can cause delays of several months after the start of the breeding
season in October/November. In most years, management only commences in
December or January, providing ample opportunities for the toad population to
increase and occupy new ponds in the first part of the breeding season. Gaining
access to numerous private properties in this high-income, low density, housing area
has been a major impediment to control, with models suggesting that missing 55% of
properties undermines the total management effort with no net effect (Vimercati
et al. 2017b; Potgieter et al. 2020, Chap. 11). The Guttural Toad management effort
has been sustained until the present, but based on the recent data researchers and
managers have discussed the possibility of changing the aim of the control operation
from extirpation to containment, because without increased effort and dedicated
long-term funding, it is unlikely that extirpation will be achieved.
646
S. J. Davies et al.