Action: American bullfrog control: Direct removal of juveniles
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- One replicated study in Belgium found double fyke nets were effective in catching bullfrog tadpoles in small shallow ponds.
- One before-and-after study in France found a significant reduction in the number of recorded adults and juveniles following the removal of juveniles by trapping, when carried out as part of a combination treatment.
Direct removal of the early lifecycle stage may offer a tool for localised population reduction when used as part of an integrated pest management strategy for controlling invasive bullfrog populations. For example, a replicated field based and modelling study from 1999 to 2003 on Southern Vancouver Island, Canada (Govindarajulu et al. 2005) found that culling bullfrog metamorphs in autumn was the most effective method of decreasing population growth rate.
Govindarajulu P., Altwegg R. & Anholt B.R. (2005) Matrix model investigation of invasive species control: bullfrogs on Vancouver Island. Ecological Applications, 15, 2161–2170.
Supporting evidence from individual studies
A replicated study in 2010 and 2011 across three sites in Belgium (Louette et al. 2014) found catchability of bullfrog tadpoles in small shallow ponds using one double fyke net for 24 h to be reasonably consistent at approximately 6%. Bullfrog populations were investigated in ten permanently wet, small, shallow fish ponds (average surface area 1,500 m2; max depth 150 cm), across three sites. In six water bodies (Hoogstraten and Arendonk), bullfrog tadpole population density was estimated. In these ponds, a number of double fyke nets were set (parallel and two meters out from the shore) for 24 h, covering all sides of the water body. A minimum of three catch efforts of equal magnitude were performed. After every catch effort, all captured individuals were removed from the population. To determine the accuracy of these population size estimates, calibration using seine netting was performed in two ponds.
A before-and-after study from 2006 to 2009 on Natural Park Périgord-Limousin sites in France (Guibert et al. 2010) found a significant reduction in the number of recorded adults and juveniles following the removal of juveniles by trapping, along with other removal methods. The number of trapped tadpoles decreased from approximately 1,600 in 2006 to fewer than 200 in 2009. Trapping was carried out as part of a combination treatment which also involved shooting of adults and collection of egg clutches. Unbaited single and double entry traps were installed equidistant from each other in the water, and were checked daily until the catch rate became negligible compared to the work effort.
- Louette G, Devisscher S & Adriaens T (2014) Combatting adult invasive American bullfrog Lithobates catesbeianus. . European Journal of Wildlife Research, 60, 703-706
- Guibert S, Dejean T & Hippolyte S (2010) Le Parc naturel regional Périgord-Limousin: territoire d’expérimentation et d’innovation par la mise en place d’un programme d’éradication de la Grenouille taureau (Lithobates catesbeianus) associé à un programme de recherche sur les maladies émergentes des amphibiens. [The Regional Natural Park Périgord-Limousin: territory of experimentation and innovation by the implementation of an eradication program of the bullfrog (Lithobates catesbeianus ) associated with a research program]. EPOPS, 79, 15-24