WAIMEA — The state plans to once again take on the rats that have colonized Lehua Island. Details will be presented Tuesday at the Waimea Neighborhood Center.
“It’s essential that we eradicate rats over there,” said Don Heacock, district aquatic biologist with the Department of Land and Natural Resources and a farmer on Kauai. “You’ll see the nesting colonies of seabirds increasing by an order of magnitude if you can get the rats.”
The island is a small, horseshoe-shaped rock about a quarter-mile north of the island of Niihau, 17 miles across the channel from Kauai.
The project entails seeding the island with rodenticide — by helicopter and with supplemental hand applications — that will kill the rats. It’s not the first attempt at the Lehua Island Restoration project.
In 2009, the state’s Department of Land and Natural Resources Division of Forestry and Wildlife partnered with the United States Department of Agriculture and did two bait drops of rodenticide over the island.
Representatives from DLNR and Island Conservation said it is critical to understand the majority of the bait pellets are cereal grains and other inert ingredients designed to be palatable to rats.
The bait contained the rodenticide at a concentration of 50 parts per million, officials say, so there were only a few ounces of the toxicant delivered to the island in the bait.
Days after the 2009 rodenticide application, thousands of fish washed up on Niihau. Within the following months, three humpback whale calves were found dead as well as a mass of squid and lanternfish.
Officials say the triggerfish samples collected from Niihau beaches for testing in 2009 showed no Diphacinone residues, which is the ingredient in the rodenticide. The tests did show presence of a blue-green algae in their stomachs. The algae produces a toxicant that kills triggerfish.
Data didn’t reveal a direct correlation between the deaths and rodenticide applications, according to previous reports, but Keith Robinson, a family owner of Niihau, voiced his doubts to TGI in 2009.
“There has never been a fish kill off like this,” he told TGI.
Robinson doubted it was a coincidence that the fish washed ashore days after the rat poison was dropped.
In April 2009, the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service determined that rodenticide did not play a part in the deaths of the three young whales that washed ashore onto Niihau, Kauai and Lanai islands between January and March 2009.
State officials told TGI recently that given the age of the whale calf found on Kauai, it would have been nursing, and its mother would not have been eating since this whale species does not feed in winter months in Hawaiian waters. The available evidence suggests that despite the coincidental timing of both events, the operations on Lehua could not have caused the death of either the fish or the whale calf, officials say.
While the rodent population was significantly reduced due to the poisoning, some rats survived, so DOFAW and its partners are taking another stab at it.
“The first attempt was a boondoggle, a total failure,” Heacock said. “They decided they were going to apply the rodenticide from helicopters.”
He explained the helicopter applications didn’t work because the island’s concave shape and inner edges make it difficult for the rodenticide to stick in places where the rats actually live.
“You’ll never get all the places that are rat habitat,” he said. “It has to be done on foot thoroughly and not only using rodenticide, but setting traps too. It has to be a full-court press.”
A stretch of rain prior to the application in 2009, and applying the rodenticide in the winter rather than in the summer, were also issues because the rats were eating newly growing vegetation — not the rodenticide.
DLNR has revamped the plan and will go over the details Tuesday.
At least three bait applications using the rodenticides Diphacinone and Brodifacoum are being proposed, according to a DLNR press release. The window of application will be July through September.
Lehua Island is home to 17 different seabird species, including three that are on the International Union for the Conservation of Nature’s Red List of Threatened Species, including the Newell’s shearwater.
It’s also habitat for the black-footed albatross and the Laysan albatross, and home to 11 plant species found only in Hawaii and 14 native plant species.
State officials say the risk to those non-target species is very low. Seabirds in particular are not a group of concern, officials said, because of their feeding behavior. They prey on live fish and marine invertebrates out at sea and do not forage for food on land.
Actions are planned to minimize the number of bait pellets reaching the ocean. However, a small amount of bait pellets are expected to reach the water, officials say.
The bait is designed to break down quickly in water, and the toxicant is not soluble in water. It will rapidly sink to the bottom of the ocean where it will eventually break down to its base components of water and carbon dioxide within as little as 30 days.
Rats, which are invasive, climb trees and shrubs, eat bird eggs, and prey on hatchlings and adult birds. They are a leading cause of the accelerated decline and extirpation of endemic Hawaiian forest birds and are a major factor limiting present populations of endangered birds.
The rats also eat seeds, bark, fruits, leaves and shoots of Hawaiian plants, hindering native plant communities.
“It’s not just about protecting the seabirds that nest over there, though,” Heacock said. “It’s about protecting Native Hawaiian culture. They use those birds to find fish and in Hawaii, fishing is in the culture.”