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| Wedgetailed Shearwater chick early August. |
There are times when doing nothing is the worst alternative.
We have the opportunity, the technology and the funding to
remove aggressive, invasive, non-native rats from the Lehua island bird
reserve. We should do it.
What a tragedy for ourselves and our descendants—not to
mention the native wildlife, if we did nothing.
The state Department of Land and Natural Resources is
proposing addressing the issue this summer, when rat populations are seasonally
low and rat food supplies are low—so they are more susceptible to attractant
bait.
(Images: A wedgetailed shearwater chick on Lehua in early August. The same chick, dead and partly eaten, presumably by rats. Credit: Island Conservation.)
The agency proposes using techniques that have been deployed
successfully on hundreds of oceanic islands around the world, including several
in the Hawaiian archipelago. It is the aerial application of rat bait
containing the anticoagulant diphacinone
And while there are risks, those risks seem minimal. There
have not been problems with injury to other species when rats were removed from
Mokoli`i off O`ahu, from Mokapu off Molokai, from Kure Atoll’s Green Island or
from Midway Atoll.
Lehua, a volcanic tuff cone islet north of Ni`ihau, is a bird refuge, but one severely compromised by Pacific rats, which have been there for decades. A dense environmental assessment for the Lehua rat removal project is available here.
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| Same chick, killed and partly eaten by rats. |
There have been angry arguments against the project, which
minimize the actual damage done by rats, and seem strongly driven by the
anti-pesticide movement. Take a look here.
Some Kaua`i residents at recent public meetings have
expressed concern over the use of rat bait near the coastline. It is a valid
concern, but there is ample evidence from previous eradication programs that
the bait breaks up in minutes in the water, and sampling has shown no active
chemical remnant in the water just days after the application.
There is no evidence of fish kills or detectable toxicity at
previous rat eradication efforts on small islets around Hawai`i.
Tests at Palmyra Atoll, which has a robust coral reef
system, showed no impact on corals from a much more dense application of rat
pellets than proposed for Lehua. A small number of shorebirds could be impacted,
but that has not been the case in previous Hawai`i eradications.
So there is a small relative risk. What’s the benefit?
Here is a paper from 2014 on the impact of rats on small tropical
islands around the world.
Rats are a problem everywhere they exist. On Lehua, swarms
of rats eat seabird eggs. They kill chicks. And they attack nesting adults. By
limiting seabird populations, they reduce the size of oceanic bird flocks that
trollers use to identify schools of fish. They even go down to the nearshore
rocks and prey on crabs and `opihi.
Rats also feed on native trees and their seeds, and are
partly responsible for the loss of Lehua’s native dryland forest. That lack of
vegetation promotes sediment runoff from the island into nearshore waters. And
they eat the insects on the island, including native insects.
And there is a long-term positive impact not only to the environment
of Lehua itself, but addressing the larger global issues facing nesting
seabird species.
One of the great benefits of promoting Lehua’s safety for
nesting seabirds is that it is a high island, and in an era of climate change and
sea level rise, it will provide nesting habitat when the low bird islands of
the Northwestern Hawaiian Islands are drowned.
This seems to be a well-thought-out project using a mature
technology, with minimal risk, and one that addresses a real environmental threat.
It is reasonable to be concerned about risks, but it is not
reasonable to refuse to act when the benefits far outweigh any theoretical risks.
© Jan TenBruggencate 2017
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