Biosecurity measures to reduce secondary spread of the invasive freshwater Asian clam, Corbicula fluminea (Muller, 1774)

Invasive species are currently considered one of the most important threats to global biodiversity. Established invaders are difficult to eradicate and management requires biosecurity measures to prevent secondary spread. Corbicula fluminea (Muller, 1774; Asian clam) has a worldwide invasive distribution and, as an ecosystem engineer, can have dramatic impacts on recipient systems, displacing native species and altering trophic structure. This study tested the efficacy of biosecurity methods for cleansing angling equipment (such as nets and waders) and other gear used in freshwater that may harbour C. fluminea and contribute to their secondary spread. C. fluminea of varying size were treated either with Virkon[registered trademark] Aquatic, common household bleach or salt at a variety of concentrations for a range of immersion times. Virkon[registered trademark] emerged as the most effective of the three treatment types and achieved 93.3% mortality when used at 2% for 5 minutes. With the bleach trials, there was no significant effect of immersion time on clam mortality, but 10% bleach for 60 minutes induced an average mortality of 76.7%. Further, maximum mortality in saltwater was only 13.3% with 60 minutes immersion. There was no significant difference in mortality among clam sizes. Virkon[registered trademark] is, therefore, recommended as the most effective product for treating angling and other gear that could potentially harbour and spread C. fluminea. We also assessed the effect of 'drying times' post-treatment and this was demonstrated to have no significant effect on clam mortality. Virkon[registered trademark] again gave the highest mortality of the three treatments, with 68.9% mortality achieved at 2% for 10 minutes. Overall, Virkon[registered trademark] emerges as an effective biosecurity measure, but further research is required to attain 100% mortality. Bleach may be useful when Virkon[registered trademark] is not available, but salt is relatively ineffective.