5. SOME ASPECTS OF CONTROL OF FRESHWATER INVASIVE SPECIES
David Aldridge, Rebecca K. Smith & William J. Sutherland
Expert assessors
David Aldridge, University of Cambridge, UK
Belinda Gallardo, Pyrenean Institute of Ecology, Spain
Trevor Renals, Environment Agency, UK
Alexandra Zieritz, University of Nottingham, UK
Scope of assessment: for the control of two invasive freshwater species.
Effectiveness measure is the median % score for effectiveness.
Certainty measure is the median % certainty of evidence for effectiveness, determined by the quantity and quality of the evidence in the synopsis.
Harm measure is the median % score for negative side-effects to non-target native species.
This book is meant as a guide to the evidence available for different conservation interventions and as a starting point in assessing their effectiveness. The assessments are based on the available evidence for the target group of species for each intervention. The assessment may therefore refer to different species or habitat to the one(s) you are considering. Before making any decisions about implementing interventions it is vital that you read the more detailed accounts of the evidence in order to assess their relevance for your study species or system.
Full details of the evidence are available at
www.conservationevidence.com
There may also be significant negative side-effects on the target groups or other species or communities that have not been identified in this assessment.
A lack of evidence means that we have been unable to assess whether or not an intervention is effective or has any harmful impacts.
5.1 Threat: Invasive amphibians
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 |
Biological control using native predators
A 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%).
A 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%).
A 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%).
A 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%).
A 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
A 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%).
A 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%).
We have captured no evidence for the following interventions:
5.2.1 Procambarus spp. crayfish
Based on the collated evidence, what is the current assessment of the effectiveness of interventions for controlling Procambarus spp. crayfish? |
|
Likely to be beneficial |
● Add chemicals to the water ● Sterilization of males ● Trapping and removal ● Trapping combined with encouragement of predators |
Unknown effectiveness (limited evidence) |
● Create barriers ● Food source removal |
Unlikely to be beneficial |
● Encouraging predators |
No evidence found (no assessment) |
● Draining the waterway ● Relocate vulnerable crayfish ● Remove the crayfish by electrofishing |
A replicated study in Italy found that natural pyrethrum at concentrations of 0.05 mg/l and above was effective at killing red swamp crayfish both in the laboratory and in a river. Assessment: likely to be beneficial (effectiveness 80%; certainty 50%; harms 0%).
A replicated laboratory study in Italy found that exposing male red swamp crayfish to X-rays reduced their mating success. A review study from the UK found that pleopod removal in male red swamp crayfish was an effective form of sterilisation, reducing population size over three years. Assessment: likely to be beneficial (effectiveness 50%; certainty 40%; harms 0%).
A controlled, replicated study from Italy found that food (tinned meat) was a more effective bait in trapping red swamp crayfis, than using pheromone treatments or no bait (control). A review study from the UK found that Procambarus spp. crayfish populations could be reduced in density but not eradicated by trapping. Baiting with food increased trapping success compared to trapping without bait. Assessment: likely to be beneficial (effectiveness 40%; certainty 60%; harms 0%).
Trapping combined with encouragement of predators
A before-and-after study in Switzerland and a replicated, paired site study from Italy found that a combination of trapping and predation was more effective at reducing red swamp crayfish populations than predation alone. Assessment: likely to be beneficial (effectiveness 50%; certainty 50%; harms 0%).
A before-and-after study from Italy found that the use of concrete dams across a stream was effective at containing spread of the population upstream. A review from the UK found barriers were effective at halting or delaying movement of the red swamp crayfish. Assessment: unknown effectiveness (effectiveness 30%; certainty 30%; harms 0%).
A replicated study in Japan found fewer red swamp crayfish in ponds containing less leaf litter. Assessment: unknown effectiveness (effectiveness 20%; certainty 30%; harms 0%).
Two replicated, controlled studies in Italy found that eels fed on the red swamp crayfish and reduced population size. Assessment: unlikely to be beneficial (effectiveness 30%; certainty 60%; harms 0%).
We have captured no evidence for the following interventions: