Invasive Species Management Options

There are four options for managing invasive species

Prevention – Prevention is better than cure. Stopping the spread of an invasive species to an island is generally the most cost-effective management option. This means that the invasive species will not be able to cause damage to the island and the need for eradication and restoration work is avoided. Preventing invasions of new invasive species should be the highest management priority even where islands already have some invasive species established. If an invasive does slip through, the focus then is on early detection and rapid response to prevent the new invasive from establishing a population.
Eradication – Eradication involves the complete removal of all individuals of a targeted invasive species population from an island. If feasible, this option offers a permanent solution if supported by biosecurity measures.
Control – Control involves containing the distribution and/or reducing the abundance of a targeted invasive species to below pre-set levels and for defined periods, so that impacts are acceptable. Control is the next preferred option when eradication is not appropriate or feasible.
No action – The ‘do nothing' option. Could be justified if -

The costs of management action outweigh the benefits e.g. it costs more to control invasive species on a crop than the value of the crop itself or -
Effective actions are not feasible or -
There is likely to be minimal impact on conservation or livelihood values.

Eradication vs. Control
To help decide between the suitability of an eradication or control approach the table below provides a detailed comparison.
Note: The table has been used for invasive mammal species in New Zealand, and is adapted from Beaven (2008).

Feature	Eradication	Control
Definition	The permanent removal of the entire population of an invasive species from an island. Usually a one-off operation done over a set period of time, and often at the time of the year when invasive species are most vulnerable to the methods being used.	The impacts of invasive species are managed by ongoing removal of the population, rather than eliminating every animal. Control is normally undertaken frequently, e.g. seasonally before a threatened species breeds.
Feasibility	Essentially only feasible on islands or behind pest-proof fences where the risks of reinvasion are relatively low or can be managed.	Potentially feasible at any defined site, but generally limited in size, especially for rodents. Continual reinvasion from outside the controlled area is a problem.
Project area	The whole project area must be comprehensively treated.	Specific areas can be targeted, and these can vary according to need.
One-off vs. continual	A one-off project with ongoing surveillance and management of reinvasion risks.	Continual management and monitoring required because if the management stops the benefits are lost.
Biosecurity	Ongoing biosecurity measures required to prevent re-invasion.	On-going biosecurity and contingency measures (for targeted species) not necessary.
Investment	High initial investment, followed by relatively low ongoing inputs (depending on the scale of ongoing biosecurity requirements).	Generally low-medium, but ongoing, investment. Potentially high long-term cost. Can be difficult to sustain with community projects.
Benefits	Significant potential benefits which improve over time. Benefits continue indefinitely if biosecurity measures maintained.	Variable benefits dependent on effectiveness of control regimes. Benefits are lost as invasive species populations rebuild if control methods are stopped.
Toxins and traps	Short term pulse of toxin or trapping, restricting the period in which there may be effects on non-target species.	Multiple, long-term use of toxins or traps increases the potential for harmful effects on non-target species. Continuous control requires the careful management of non-targeted effects, which can constrain the type of control tools used.
Adapting	Target invasives do not have time to adapt to the methods used against them.	Target invasives can potentially adapt to control methods making the control less effective over time.