Large-scale control of Australian possums throughout New Zealand uses toxic cereal baits containing 1080 (sodium fluoroacetate). These baits are often aerially applied over rough terrain where ground application is impractical. Many small streams flow in these areas, so 1080 baits can potentially fall into them. The ecological effect of 1080 leaching from baits was assessed on freshwater fish and invertebrate communities in four streams using a BACI experimental design. Four sites were selected in each stream: 10 m and 100 m below and 10 m and 100 m above where 1080 baits were placed. All sites were monitored 4 days and 1 day before and after baits were added, respectively. Separate experiments were conducted to assess impacts of 1080 on native fish and invertebrate communities. Baits were added to each stream to achieve bait densities 10 x greater than found after normal control operations. Three species of native fish, longfin eels (Anguilla dieffenbachii), koaro (Galaxias brevipinnis), and upland bullies (Gobiomorphus breviceps) were placed into separate cages at each site in each stream, and mortality monitored during the experiment. Analysis of water samples collected during the fish experiment showed that 1080 was detected only for 12h, and at low concentrations (c. 0.2 mu g litre(-1)), despite the large number of baits placed in each stream. No fish died after addition of 1080 baits, suggesting that all three species were tolerant to dissolved 1080 at concentrations observed in this study. Invertebrate communities were quantified by sampling 10 replicate rocks at each site. Caddisflies (Helicopsyche, Pycnocentrodes, and Pycnocentria), orthoclad midges, and the mayfly Deleatidium dominated the community. 1080 had no detectable effects on the invertebrate community. These results suggest that 1080 leaching from submerged baits in small streams has no demonstrable biological impacts. Based on this finding, the need to maintain buffer zones around large waterways as some councils require is questioned.
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