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What Works in Conservation 2015

 | 
William J. Sutherland
, 
Lynn V. Dicks
, 
Nancy Ockendon
, 
et al.

5. Some aspects of control of freshwater invasive species

5.1. Threat: Invasive amphibians

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5.1.1 American bullfrog Lithobates catesbeiana

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for controlling American bullfrogs?

Likely to be beneficial

● Biological control using native predators
● Direct removal of adults
● Direct removal of juveniles

Trade-off between benefit and harms

● Draining ponds

Unknown effectiveness (limited evidence)

● Application of a biocide
● Biological control of co-occuring beneficial species
● Habitat modification

No evidence found (no assessment)

● Collection of egg clutches
● Fencing
● Pond destruction
● Public education

Likely to be beneficial

Biological control using native predators

1A replicated, controlled study on a former outdoor fish farm in northeast Belgium found the introduction of the northern pike led to a strong decline in bullfrog tadpole numbers. Assessment: likely to be beneficial (effectiveness 70%; certainty 40%; harms 0%).

Direct removal of adults

2A replicated study in northeast Belgium found catchability of adult bullfrogs in small shallow ponds using a double fyke net for 24h to be very low. A short form report on a replicated, controlled study in the USA found that bullfrog populations rapidly rebounded following intensive removal of the adults. A short form report on an eradication study in France found a significant reduction in the number of recorded adults and juveniles following the shooting of metamorphosed individuals before reproduction, when carried out as part of a combination treatment which also involved trapping of juveniles and collection of egg clutches. A modelling study found that a mortality of 65% or greater every two years is required to make shooting bullfrog adults beneficial for red-legged frog persistence. Assessment: likely to be beneficial (effectiveness 50%; certainty 70%; harms 0%).

Direct removal of juveniles

3A replicated study in Belgium found double fyke nets to be very effective in catching bullfrog tadpoles in small shallow ponds, and a modelling study found that culling bullfrog metamorphs in autumn was the most effective method of decreasing population growth rate. A short form report on an eradication study in France reported 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 with also involved shooting of adults and collection of egg clutches. Assessment: likely to be beneficial (effectiveness 70%; certainty 60%; harms 0%).

Trade-off between benefit and harms

Draining ponds

4A replicated study in cattle ponds in the USA and a modelling study found that draining invaded waterbodies reduced or eradicated bullfrog populations. However, drying cattle ponds negatively affected salamanders by preventing breeding. Assessment: trade-offs between benefits and harms (effectiveness 60%; certainty 40%; harms 90%).

Unknown effectiveness (limited evidence)

Application of a biocide

5A replicated, controlled laboratory study in the USA reported a number of lethal toxicants to the American bullfrog, including caffeine (10% solution), chloroxylenol (5% solution), and a combined treatment of Permethrin (4.6% solution) and Rotenone (1% solution). Assessment: unknown effectiveness (effectiveness 50%; certainty 20%; harms 0%).

Biological control of co-occuring beneficial species

6A replicated, controlled field experiment in the USA found that the presence of the invasive bluegill sunfish increased the survival rate of bullfrog tadpoles by reducing the abundance of indigenous, predatory dragonfly nymphs. Assessment: unknown effectiveness (effectiveness 30%; certainty 20%; harms 0%).

Habitat modification

7A three year field survey in the USA found bullfrogs to be less abundant in ponds with shallow sloping banks and extensive emergent vegetation. Assessment: unknown effectiveness (effectiveness 30%; certainty 20%; harms 0%).

No evidence found (no assessment)

8We have captured no evidence for the following interventions:

  • Collection of egg clutches
  • Fencing
  • Pond destruction
  • Public education

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