The state has completed its final round of rat-killing pellet bombing at Lehua Island as it awaits test results on what caused the recent deaths of dozens of fish and two birds.

The third and final application of bait pellets containing the poison diphacinone rained down on the 284-acre island Tuesday. A pesticides inspector from the state Department of Agriculture was on hand to monitor the helicopter drop.

Suzanne Case, director of the Department of Land and Natural Resources, said there were no dead birds or fish in evidence Tuesday. A team will continue to monitor the area.

Last week the state launched an investigation after being alerted to dead fish and birds via photos and video posted on social media. A team collected 45 dead mullets and two dead juvenile boobies from a tide pool on the island.

Case said the cause is under investigation and that the state and federal agriculture departments are testing specimens, which showed no immediate exposure to rodenticide. Further testing could take months.

Some community members on Kauai, including state Rep. Dee Morikawa (D, Niihau-Koloa-Kokee), have raised concerns about the use of diphacinone to eradicate rats and whether the rodenticide harms other wildlife.

“Don’t tell me it’s a coincidental death that occurs because of warm waters. No, it has to be because of the pellets,” said Morikawa.

In response to concerns, Case said the department has imposed additional buffers in the area where the dead fish were found and has ramped up monitoring efforts.

Coincident with the investigation, Morikawa sent a letter to Case last week requesting the state delay the third application until the tests results are in.

“The rat eradication project by the state clearly may be causing these deaths and that poison could enter our food chain threatening the lives and livelihoods of Kauai residents,” Morikawa said in the letter. “It is critical to understand the facts of these deaths before potentially causing much more serious problems that could be avoided by taking the time to understand the threat to our residents.”

Case responded to Morikawa on Tuesday in a letter indicating the state has requested expedited tests on tissue samples. She conceded a delay could lead to additional applications and costs and that the state’s goal is to complete the bait drops before the rainy season.

Case said the department and its contractors have been upfront on possible risks to nontargeted species.

“There are many possible causes for the mortality of the 45 fish and two birds recently collected. Supported by well-researched science, and daily monitoring, it remains unlikely that the rat eradication project is leading to rodenticide in the marine food chain. We do not feel this incident constitutes an unacceptable risk, when weighed against the long-term benefits of creating a Lehua Island free from non-native, invasive rats that have been eating seabirds, their chicks and eggs for more than 75 years,” she said.

At a news conference Tuesday afternoon, Case said it’s important to keep in mind similar applications have been conducted worldwide more than 500 times.

She said they “are very confident that the long-term conservation benefits for the seabirds on Lehua Island are far outweighing any short-term potential risks.”

The first and second bait applications took place Aug. 23 and 30, respectively. The state’s goal is to create a predator-free sanctuary for endangered and threatened seabirds.

“Lehua Island is one of the most important nesting sites in the main Hawaiian Islands, and invasive rats have been eating these native birds and chicks and eggs for the past 75 years and some seabirds are thought not to be there anymore because of the rats,” Case said. “We have to remove every single rat from the island to make it safe, because a breeding pair can completely re-infest the island in months.”

Lehua Island is just north of Niihau, separated by a 2,500-foot channel.