The successful elimination of Cane toads, <Emphasis Type="Italic">Bufo marinus</Emphasis>, from an island with breeding habitat off Bermuda |
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Authors: | David B Wingate |
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Institution: | (1) Bermuda Aquarium Museum and Zoo, PO Box CR86, Crawl CRBX, Hamilton Parish, Bermuda |
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Abstract: | The 6.5 Ha Nonsuch island nature reserve in Castle harbour, Bermuda, under restoration as a “Living museum” of Bermuda’s pre-colonial
terrestrial flora and fauna since 1962, was unexpectedly compromised by the colonization of a manmade freshwater pond by the
invasive Cane toad Bufo marinus, which managed to cross a 175 m seawater barrier isolating the island. The toad was considered to pose a threat to the endemic
Skink, for which Nonsuch is a key sanctuary, and to the burrow nesting Bermuda petrel or Cahow, which was about to be translocated
to that larger island in order to establish a colony safe from the global warming threat of sealevel rise. A non-lethal method
of removing the toads was devised through installation of a toad barrier around the freshwater pond, constructed of robust
high density polyethylene (HDPE). Toads outside the barrier were no longer able to breed and were captured and removed by
night searches over a five year period as they piled up against it. Removal of the breeding population inside the barrier
was only possible by capturing all individuals resulting from each spawning before they could reach breeding age. This also
took 5 years despite the small size (0.06 Ha) of the pond. A total of 1,244 toads were removed to Bermuda’s mainland. As breeding
age is attained in 2 years the collection total for the first 2 years provided an approximation of the population density
on the island before removal began (~80 per Ha). Although the immigration rate to Nonsuch is estimated to be less than one
per year, this still requires maintaining the barrier as a permanent fixture. As future immigrants can be fairly quickly intercepted,
the toad is now essentially extaxic on Nonsuch. This is the first published report of a successful eradication of the species
from an island with breeding habitat. |
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