The purpose of biosecurity is to:
- Keep the island free of the target species you have eradicated
- Keep the island free of new invasive species
- Prevent the export of invasive species from the island to other islands.
Biosecurity activities involve: prevention, surveillance and management of incursions of invasive species.
Removal of one invasive species can make the island more vulnerable to other invasive species e.g. the eradication of Norway rats (Rattus norvegicus) from Raoul Island, New Zealand may have significantly increased the chances of mouse (Mus muscles) survival and colonisation, should an incursion occur. So the Biosecurity Plan must consider all possible invasive species; not just the target species.
The routes that invasive species take to arrive at an island are called pathways. Most pathways are due to people and goods travelling to the island by boats. Therefore much of the work in the Biosecurity Plan involves working with visitors to the island to prevent this happening. However, rats can swim considerable distances and can invade islands without the help of people – this biosecurity threat also needs to be managed.