State drops bait with rat pesticide on Lehua Island

Photo: DLNR

On Wednesday, the state Department of Land and Natural Resources began a project to eradicate rats on Lehua Island, a small, crescent-shaped island just off Niihau, west of Kauai.

Lehua is one of the largest and most diverse seabird colonies in the main Hawaiian Islands with 17 seabird species and 25 native plants. DLNR says invasive rats threaten that ecosystem by eating the seabirds and destroying native plants.

In order to create a predator-free environment, the state applied the first of three rounds of bait containing a small amount of rodenticide on the island by helicopter, with some crews on the ground distributing the bait by hand.

The department said in a press release: “The operation was executed as planned—successfully, safely, and under the close watch of regulators from the Hawaii Department of Agriculture and an independent monitoring team from the U.S. Department of Agriculture.”

State Rep. Dee Morikawa, D, Niihau, Lehua, Koloa, Waimea, expressed serious concerns about the project. She says she was hoping for another alternative.

“People are saying they can do more a precise drop of the poison. They can do bait stations and have them monitor them,” she said. “There’s a bait that sterilizes the rat and over time, the rats will eventually disappear. Pretty much they just want people on the ground to do it more safely, so that they can make sure it doesn’t fall into the ocean.”

According to DLNR, “After exhaustive evaluation of scientific publications and hundreds of island invasive species eradications around the world, the Lehua Island Restoration Steering Committee determined that the only feasible method for safely removing rats is the deployment of bait containing a small amount of rodenticide.  The committee chose urgent intervention over allowing Lehua’s invasive rats to continue to devastate birds, plants, marine waters, cultural sites and resources.”

The operation was executed with the approval of dozens of state and federal permits, including one issued Tuesday by HDOA. Agriculture chairman Scott Enright observed the operation from a helibase on Niihau.

“I am pleased with the planning, preparation and execution of this project to restore Lehua Island. It was carried out very professionally and with the utmost care,” he said.

Officials say the bait presents very little risk to marine and other wildlife:

“Diphacinone, being almost insoluble, scarcely dissolves in water and thus most remains in bait pellet fragments on the sea bottom. Diphacinone breaks down quickly in water when exposed to ultraviolet light (e.g. sunlight) —  a likely fate for some drifted bait. Eventually, the rodenticide decomposes into carbon dioxide and water and intermediate compounds in its decomposition process are non-toxic. In hundreds of similar projects, no documented impacts to marine mammals or corals have been documented, and invertebrates are not affected at all as they do not metabolize diphacinone. Thus, regulators concluded that marine life will have little to no exposure to the negligible amount of rodenticide that drifts into the water.”

View the Lehua Island Restoration Project Final Environmental Assessment for more information.

Lehua Island (Photo: DLNR)

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