State Proceeds with Lehua Island Rat Eradication

August 23, 2017, 4:18 PM HST
* Updated August 23, 4:26 PM

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The state Department of Land and Natural Resources began aerial application of rodenticide today in an attempt to control the rat population at Lehua Island, an area managed as a State Seabird Sanctuary. A permit allowing aerial application of the restricted-use pesticide was approved by the state Department of Agriculture on Tuesday.

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State officials say the HDOA had worked closely with state lawmakers in addressing the Kauaʻi community’s concerns to ensure that appropriate safety measures and procedures were developed to minimize any adverse effects to marine mammals, fish and wildlife.

“Dozens of Federal and State permits affirming that the operation poses very little risk to people, marine mammals, fish, sea turtles, birds, or other wildlife were secured in advance of the operation,” officials with the state Department of Land and Natural Resources said today.

“The operation was executed as planned—successfully, safely, and under the close watch of regulators from the Hawai`i Department of Agriculture and an independent monitoring team from the US Department of Agriculture,” according to a statement released by the DLNR.

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Rep. Daynette Morikawa had sought a delay of the planned rat eradication project as well as answers to environmental questions. In a letter to department officials, Rep. Morikawa raised concerns over potential impacts to aquatic life, endangered species and fish near the island.

According to the DLNR, fish are among the least likely animals to be affected by the rodenticide. Department officials say that what little bait drifts into water from the over-land application, sinks to the sea floor and degrades quickly.

The first of three rounds of conservation bait were applied to Lehua Island today by helicopter, with supplemental applications conducted by hand. The permit states that no aircraft application shall be conducted when wind velocity exceeds 25 mph for aerial applications of the diphacinone rodenticide bait.

Sheri Mann, Kaua‘i branch manager for the DLNR Division of Forestry and Wildlife (DOFAW) which manages Lehua Island as a State Seabird Sanctuary, said, “About 99.995% of the bait used is comprised of non-toxic, human food-grade ingredients made to attract rats. The remaining fraction is diphacinone, a first-generation anticoagulant rodenticide.”

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Hawai‘i Department of Agriculture Chair Scott Enright approved the aerial application permit, necessary for the project to move forward. He observed today’s operation from the helibase on Ni‘ihau and commented, “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.”

Lehua is one of the largest and most diverse seabird colonies in the main Hawaiian Islands with 17 seabird species and 25 native plants (14 Hawai`i endemics – occurring nowhere else in the world) inhabiting the steep, rocky, windswept slopes of the tiny island. Lehua is an important part of native Hawaiian culture—the Ni‘ihau community gathers ‘opihi (limpets) in adjacent marine waters and on the island are several important native Hawaiian cultural sites.

Lehua Island’s natural ecosystem supports one of the largest and most diverse seabird colonies in the main Hawaiian Islands. This includes the International Union for Conservation of Nature Red List[1] Endangered Newell’s Shearwater and two IUCN Near Threatened Species, which are also US Federal Species of Concern, the Black-footed and Laysan Albatross.

Lehua Island is located about 19 miles west of Kaua‘i and less than a mile north of Niʻihau. It is a 111 hectare, crescent-shaped, and uninhabited island administered by the US Coast Guard and managed by the Hawai‘i Department of Land and Natural Resources.

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The invasive rats forage on native plants and seeds, which imperils the entire ecosystem. These impacts can contribute to erosion which can in turn impair near-shore marine and coral ecosystems and fisheries. Native birds like the threatened Newell’s Shearwater are likely being restricted from breeding on Lehua Island due to predation by rats. Smaller, open-nesting seabirds such as terns and noddies are conspicuously absent from Lehua (save small numbers found in sea caves), also a suspected artifact of rat predation. Invasive rats ravage other threatened birds.

DLNR Chair Suzanne Case concluded, “A safe, careful, by-the-book operation, together with the downstream conservation outcomes of this project in coming years, will provide the proof-of-concept the community is seeking for this important conservation intervention”. Two additional applications of rodenticide are planned in the next few weeks depending on weather conditions.