If all goes as planned, Lehua Island, a 284-acre state-designated seabird sanctuary less than a mile north of Niihau, will be rat-free in the near future.

But that’s a big “if.”

The state Division of Forestry and Wildlife, the lead agency on the Lehua Island Eradication/Restoration Project, must still obtain a permit from the state Department of Agriculture’s Pesticide Branch to aerially apply restricted use pesticides.

Lehua Island would be more of a sanctuary for seabirds if not for the rats. Island Conservation

The pesticides being considered are the anticoagulants diphacinone and brodifacoum, both of which have been used to successfully eradicate rodents from islands, according to a draft environmental assessment for the project released last month.

When DOFAW first tried to eradicate the predatory rats from Lehua several years ago, it chose to use just diphacinone, which is considered less of a threat to non-target species than brodifacoum. Even so, the Pesticide Branch chief at the time, Robert Boesch, directed DOFAW’s contractor not to distribute any rat bait within 30 meters of the water, so as to limit any potential harm to marine life.

When loads of dead fish and a whale calf washed up on the shores of Niihau and another calf washed up on Kauai after the January 2009 rodenticide drop, Boesch’s agency imposed a ban on aerial baiting on Feb. 5, 2009, “until general conditions around testing guidelines for rodenticide impacts in marine environments were developed” by the Environmental Protection Agency, states a January 2011 independent review of the project.

That review, by New Zealand’s Landcare Research, cited the DOA’s requirement of a coastal buffer as one of several possible contributors to the project’s failure.

Boesch retired several years ago and it’s unclear whether or not the DOA will maintain his position. Steve Russo of the Pesticide Branch said late last month that he hadn’t yet read the draft environmental assessment and could not say what his agency’s position would be without first seeing a permit application.

The Department of Land and Natural Resources, DOFAW’s parent agency, and contractor Island Conservation stated in a joint email to Environment Hawaii, “Until the EA process is complete, discussion of the operational details (including the presence or absence of buffer) would be premature. However, the EA outlines the well-established principles of rat eradication that highlights the need to place bait into every potential rat territory to ensure a reasonable probability of success.

The coastal fringe of the island is important habitat for rats and removal of rats in these habitats would include any or a combination of broadcast application up to the high-water mark, bait station placement and/or hand placement of bait and/or traps to ensure removal tools are placed into every potential territory.”

Should the DOA grant the permit and the eradication effort succeed, one of the largest and most diverse seabird colonies in the main Hawaiian Islands will “have the potential to become a refuge to species displaced by sea level rise,” the EA states.

Tragic Trilogy?

“This one made me cry,” said Boesch in an interview, pointing to a photo of the dead humpback whale calf that had washed up on Niihau shortly after the Lehua diphacinone broadcast in 2009. He had included the picture in a Power Point presentation he gave at a May 14, 2009, Western Region Pesticides Meeting. The presentation — as well as his unpublished paper, “Did Rat Bait Kill Humpback Whale Calves in Hawaii?” — includes a litany of non-target species deaths that he believes resulted from past large-scale uses of diphacinone for rat control in the state.

In late 2003, when diphacinone was dropped by helicopter on Keauhou Ranch near Volcano village, on the island of Hawaii, and was, without authorization, loaded into several bait stations at the treated plot’s perimeter, feral pigs broke into the bait stations and also likely consumed large quantities of the aerially broadcast bait. Shortly afterward, 12 feral pigs were found dead. Another pig — a 185-pound boar — that had been radio-tracked was captured alive, killed, and tested for diphacinone residues.

Boesch, who worked for the EPA before joining the DOA, noted in his paper that the amount of diphacinone found in the dead pigs was a fraction of that found in the living pig (which he refers to as ‘pig number 1’). This, he argued, illustrates the wide sensitivity range among individuals of a single species.

Non-lethal bait is spread over Lehua in a September 2015 experiment. The state would like to again dispense actual pesticides to eradicate rats. Department of Land and Natural Resources

“What might happen with the pigs that survived?” he asked in his paper. “Hunters and their families consuming liver from pig number 1 would be exposed to a significant amount of diphacinone.”

In 2007, the state sought to do a diphacinone broadcast on Mokapu, a rock peak off Molokai. At the time, diphacinone was not allowed to be applied directly to water or intertidal areas and the DOA refused to issue a permit. The EPA, however, removed its restriction regarding applications in water in December 2007, thereby allowing the project to proceed in February 2008.

Thirteen days after the bait application, a juvenile humpback whale stranded on a Maui beach about 40 miles from Mokapu. The U.S. Geological Survey, which tested liver samples taken from the whale, was unable to detect diphacinone.

Less than a year later, nearly four tons of diphacinone bait were aerially applied to Lehua. Dead fish and a juvenile whale reportedly washed up on Niihau within days. Within weeks, another juvenile whale washed up in Kekaha, Kauai, although no diphacinone was detected in tissue samples taken.

Boesch argues that the tests used to detect diphacinone in the tissues of non-target species can’t detect levels that result in harm, and because the EPA has lifted its restriction on applying diphacinone to water, rat eradication programs are “largely unenforceable.”

He insists that the tissue samples of the dead fish from Niihau contained a chemical signature that, while not identifiable as diphacinone under the tests’ detection limits, could have been an indicator of diphacinone poisoning.

Post Mortem

Seven months after the baits were dropped on Lehua, rats were seen on the island. In its 2011 report to the Department of Land and Natural Resources on the project’s failure, Landcare Research explained that no independent quality assurance of the diphacinone bait had been done, that the DOA’s instruction that no bait fall into the sea or within 30 meters of it constrained coverage, and that the bait was applied after a rainfall event “that triggered a flush of green vegetation with more abundant natural food that might have been more palatable than the cereal baits.”

The company also noted that the permit’s expiration date — March 1, 2009 — made it impossible for project managers to reapply bait in response to evidence of surviving rats, since the rats weren’t seen until August. What’s more, funding issues and regulatory concerns over the fish deaths confounded efforts to use ground-control methods, the report stated.

Lehua Island is home to birds such as this red-footed booby chick, but they are threatened by rats. Island Conservation

Landcare suggested that a freshwater algae toxin detected in the stomachs of some of the fish suggests that their death may have been due to land-based runoff. No diphacinone residues were detected in any of the fish tested and “logically one would expect that the larger the kill, the less likely it could have been caused by the limited number of baits that may have fallen into the sea,” the report stated.

Agency responses to the fish kill were “outpaced by media and internet coverage, and by alarmist presentations” — here, they cite Boesch’s power point presentation — “all of which served to convey a message of an adverse outcome of the Lehua operation that was not borne out by the eventual test results,” the report stated.

Robin Baird, a cetacean expert with the Cascadia Research Collective, says the likelihood that the humpback calf fatalities were caused by diphacinone is “extremely, extremely small.” Regarding the possibility that calves might have consumed diphacinone through their mothers’ milk, he echoed an observation in the EA that female humpbacks don’t feed in Hawaii.

Marine Impacts

In its EA, the DLNR stresses the need for the next Lehua eradication effort to be unrestricted by a coastal buffer requirement. To assess potential marine impacts, the DLNR conducted a test run in 2015 using an excessive amount of inert bait pellets. More fish interacted with the bait than in a similar 2008 survey, but the application rate was also much higher. The EA also notes that recent studies of three fish species that may eat the bait indicate that they are amongst the least sensitive animals to diphacinone.

Brodifacoum, however, was found in mullet found dead after bait was applied to Palmyra Atoll in 2011.

Regarding possible risks to cetacean species found in waters surrounding Lehua, the EA only comments on the dead humpback whale calves from 2009, noting that they would have fed exclusively on milk and had “no possible contamination pathway by diphacinone.”

Baird told Environment Hawaii that with regard to the potential danger to whales and dolphins that live around or travel past Lehua, “The animals have more to worry about” — such as persistent organic pollutants or toxin-laden agricultural runoff — “than a one-time use of a rodenticide.”

Although monk seals do haul out on Lehua’s rocky ledges, the EA states that the insolubility of both diphacinone and brodifacoum ensure that the seals won’t absorb any dissolved rodenticides through their skin. Although the seals could potentially be exposed if they ate contaminated fish, the EA notes that there is no reef surrounding Lehua Island and no lagoon, “minimizing the potential for fish to consume spilled bait.”

To prevent bait from falling into the water, the bait hoppers will have a deflector that spreads bait out to only one side, the EA states, adding that pellets would also not be applied in winds greater than 35 mph or when heavy rains are expected.

Even if all of the bait were dropped into the ocean, both rodenticides would quickly dissolve “to vanishingly small concentrations,” the EA states.

Reprinted with permission from the current issue of Environment Hawaii, a non-profit news publication founded in 1990. All issues published in the last five years are available free to Environment Hawaii subscribers at www.environment-hawaii.org. Non-subscribers must pay $10 for a two-day pass. All issues older than that are free to the public.

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