Monday, November 24, 2008

The greening of Lehua Island

No one alive knows what the environment on Lehua Island was like before the rats and rabbits arrived.

These critters began eating virtually every seed and seedling, leaving it an eroded crescent of earth, rock and cinder.

But there is enough evidence to make educated guesses about what the island was like before human interference, and restoration teams will now try to recreate the prehistoric Lehua.

(Image: Lehua from the air. Credit: NASA image via Google Earth.)

A supplemental environmental assessment for the restoration project has been completed by the U.S. Fish and Wildlife Service and the state Department of Land and Natural Resources' Division of Forestry and Wildlife. It updates a 2005 environmental assessment, changing the timing of rodent control efforts to reduce threats to birds, and building on information developed during a similar program at an islet off Molokai.

Lehua is a gorgeous speck of land, even without restoration. An ancient tuff cone, it sits just north of Ni'ihau, visible on a good day from west Kaua'i, 20 miles distant.

Sixteen species of seabirds use its 310 acres. Seals haul out on its rocky shelves.

It is surrounded by deep, clear waters favored by dive tourists. One arm of its curved shape has a deep vertical crack that extends down into the sea. Some folks call it the Keyhole. Multicolored corals and reef fishes cruise the steep-bottomed and sheltered arc of its bay.

But the land is mostly shades of volcanic brown. Little vegetation survives on the island.

As the environmental assessment says, it's been clear at least in the scientific literature since 1931 that rats and rabbits were the main problem. It's taken more than 70 years to move from that recognition to doing something about it.

There have been past efforts to control the rats and rabbits—reportedly left by European sailors to provide familiar sustenance for shipwrecked sailors. The rabbits were eradicated by hunting during the past three years, and government now proposes to remove the rats as well.

Says the press release announcing the completion of the environmental assessment:

“The project will protect and restore native populations of seabirds, plants, and other wildlife on Lehua by eradicating rats, an invasive species damaging the island’s ecosystem.

“Rats are known to have eliminated many seabird species from islands around the world by eating bird eggs and preying on live birds. They also feed on native plants and insects, suppressing or eliminating populations of these species as well.

“Once the rats are removed, a plant restoration project will follow increasing habitat for native birds and insects.”

The proposal is to use rat baits, both in types and in ways that are unlikely to impact nesting and roosting bird populations—including doing the project in winter, when the fewest nesting seabirds are present.

The rodenticide of choice is diphacinone, which was recently used to remove rats from Mōkapu Island off north Molokai. It is highly toxic to rats, less toxic to birds and at Mōkapu, tests after use did not find traces of the chemical in marine resources next to the island.

Researchers will keep an eye on the island to see what native plants may begin growing in the absence of the rats and rabbits, but also to see whether weeds begin pushing in. They also propose to plant natives that are known from Lehua and similar offshore islets, but which are not not present.

Copies of the environmental assessment are available at the Fish and Wildlife Service website at, or you can call the Pacific Islands Fish and Wildlife Office at 808-792-9400.

©2008 Jan TenBruggencate

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