Bullfrog management in Flanders (north Belgium): Are we aiming high enough?

American bullfrog Lithobates catesbeianus is one of the world’s worst invasive
species and suspected to cause substantial ecological damage around the globe
through predation, competition and pathogen transmission. The species has
been introduced in Flanders at the end of the 1990s. Since then the population
has been expanding its distribution area, and now holds an area of occupancy
of 17 km2. The largest stronghold is a (meta)population in a river valley where
a large reproducing population in a complex of several hundreds of - largely
private - ponds used for recreational fishing and gardening is present. The
north of the province of Antwerp is home to a few smaller isolated populations.
To halt the spread, and reduce its impact on native biota, regional and local
authorities, ngo’s, conservation managers, a social economy company and
scientists worked together in the cross-border EU co-funded Interreg project
Invexo (www.invexo.be). Attempts were undertaken to eradicate the smaller
populations, using a variety of active trapping techniques. Research was
performed into cost-effectiveness of double fyke nets. This catching gear is
relatively cheap, easy to handle and know has documented catchability for
both larval and adult stages, thereby offering some perspectives for integrated
control of populations. Management followed a holistic approach, integrating
active removal with habitat management by introduction of native predatory
fish, which has been shown to increase the general quality of the aquatic habitats
involved. Meanwhile, risk analysis was performed for bullfrog in Belgium in
order to underpin legislative action to prevent new incursions.