Environmental Engineering Reference
In-Depth Information
for the Galapagos Islands (B. Milstead pers. comm.), for Mediterranean islands
(Genovesi 2005; P. Genovesi pers. comm.), for the Pacifi c (Sherley 2000), for the
Aleutian Islands (G. Howald pers. comm.), and for Mexican islands (A. Aguirre
pers. comm.). National plans are in preparation for introduced rodents on
Australian islands and for all biosecurity issues in Mauritius. To a large extent these
national and international plans should reinforce the fl ow of funds for eradication
attempts in the near future. A caution for enthusiasts is that institutional commit-
ment can as easily turn off if a few high-profi le attempts fail because of foreseeable
fl aws in the planning process.
A strategy between eradication and sustained control is where it is technically and
logistically possible to remove all the target pests or weeds, but where immigration
is certain, more-or-less frequent, but manageable. Three versions of local elimin-
ation of mammal pests are being implemented in New Zealand:
•
First, pests such as stoats have been removed from several islands in Fiordland.
However, the islands are all within swimming distance for stoat populations
on the adjacent mainland (King and Murphy 2005) and so immigration is
likely and in fact the frequency has been measured for one island cleared of
stoats (Parkes and Murphy 2003).
Second, areas of native vegetation are enclosed with fences that restrict immi-
•
gration of all alien mammals ('mice to deer' is the claim) and the resident
populations of such mammals within the 'mainland island' are eradicated
(Parkes and Murphy 2003).
Third, as we know from islands, some pest species can be eradicated with a
•
single application of a control method. Trials are being conducted for some
key pests on parts of New Zealand's main islands to compare the costs of
achieving zero density (and managing buffers to slow immigration) with the
costs of a normal sustained control strategy with higher residual densities and
more frequent control operations (Morgan
et al
. 2006).
So how much have we progressed in halting the homogenization of the world's
biota since 2001? First, the bad news. A glance at journals such as
Biological
Invasions
suggests the answer is 'not a lot' for continental mainlands, not much
either on mainlands or islands for weeds or invertebrates, and hardly at all for
marine species. The answer is also not much for vertebrates used within the pet
trade—Australia, for example, has 1200 fi sh species kept in the pet trade of which
485 may still be legally imported, and 35 of which (so far) have established wild
populations (Vertebrate Pest Committee, unpubl. data). However, most countries
are attempting to regulate the legal importation of risky new species (e.g. Bomford
