Brodifacoum rat poison has been detected in Blue Cod after an aerial poison operation was carried out across Ulva Island, in August, and a follow up drop in September.
The drop was targeting rats, but many birds, some endangered, are expected to have been killed. Monitoring is reportedly being carried out on endemic robin, saddleback, and weka.
30 blue cod were being monitored, and the poison has so far been detected in 2 of them. Brodifacoum is lethal to aquatic life, and extremely persistent.
After a similar drop last year across Rangitoto Island, off the shores of Auckland, many hundreds of native birds were killed. The poison was detected in penguins, and also suspected of killing fish-life, many dolphins, and a whale.
Ulva Island was declared rat-free in 1997, after successful trapping programs. However, rats were detected on the island again last year, so the Department of Conservation decided that an aerial operation was the best way to ensure the rats are eradicated again.
The operation has caused a lot of controversy, with many arguing that with a land area of around 600 acres, it could easily be managed with trapping and bait stations, like it was in 1997, and that the kill of native wildlife will be too great to warrant an aerial poisoning operation.