It's the DLNR's second attempt after efforts failed in 2009, but Fishermen are worried the poison will end up in the ocean and harm marine life.
After past drops, dead fish washed up on Niihau and a whale calf beached itself.
"It's a bad idea with the research we've done and found out compared to what they're saying," said Harold Vidinha wuth Kekaha Hawaiian Homestead Association. "There's other ways to do this. More expensive, but a lot safer."
"We may never know exactly for sure what caused the event in 2009, but we know that Diphacinone was not found in those fish tissues," said Josh Atwood, DLNR State Invasive Species Coordinator. "We don't anticipate that they were connected at all."
DLNR says that although cats and rats have become a focal point at this stage in the project, pigs and owls are also predators that have had detrimental effects on the birds' survival.