Estimating the value of quarantine: eradicating invasive cane toads from tropical islands

Islands are increasingly used to protect endangered populations from the negative impacts of invasive species. Quarantine efforts on islands are typically undervalued, however. Using a field-based removal experiment, we estimate the economic value of quarantine efforts aimed at keeping invasive cane toads (Rhinella marina) off Australian islands. We estimate a mean density of 3444 [2744, 4386] individual toads per km2 and a mean per-night detection probability of 0.1 [0.07, 0.13]. Using a removal model and estimates of economic costs incurred during toad removal, we estimate that eradicating cane toads would cost AUD$96,556 per km2. Across islands that have been prioritized for conservation benefit across the toads predicted range, we estimate the remaining value of toad quarantine to be more than $1.3 billion. The value of a proposed waterless barrier on the mainland to prevent the spread of toads into the Pilbara was in excess of $26 billion. We conclude that quarantine of toads across Australia provides substantial value in prevented eradication costs.