State, Federal Agencies Try Again To Rid Lehua Island of Rodents

posted in: April 2017 | 0
Red-footed booby chick on Lehua island. Credit: Island Conservation
Red-footed booby chick on Lehua island. Credit: Island Conservation

If all goes as planned, Lehua island, a 284-acre state-designated seabird sanctuary that’s less than a mile north of Ni`ihau, will be rat-free in the very near future.

But that’s a big “if.”

Among other things, the state Division of Forestry and Wildlife (DOFAW), the lead agency on the Lehua Island Eradication/Restoration Project, must obtain a permit from the Pesticide Branch of the state Department of Agriculture (DOA) to aerially apply restricted use pesticides. In this case, the pesticides being considered are the anticoagulants diphacinone and, possibly, brodifacoum, both of which have been used to successfully eradicate rodents from islands elsewhere, according to a draft environmental assessment for the project released last month.

When DOFAW first tried to eradicate rats from the island several years ago, it dropped its original proposal to use brodifacoum as a back-up to diphacinone. Diphacinone has a lower success rate and is not as commonly used for island eradication projects, but it is considered less of a threat to non-target species. 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 Ni`ihau and another calf washed up on Kaua`i after the January 2009 rodenticide drop, Boesch’s agency imposed a ban on aerial baiting on February 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.

The draft EA — which has a preferred alternative of using diphacinone first and brodifacoum only if necessary — states that the project will be more effective without the coastal buffer, “thus ensuring a uniform and complete distribution of bait in shoreline areas used by rats.”

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 Hawai`i, “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 ultimately 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 draft EA states.

The comment period for the draft EA ends April 6. The U.S. Fish and Wildlife Service, a participating agency in the project, is also expected prepare its own analysis.

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 Ni`ihau shortly after the Lehua diphacinone broadcast in 2009. He had included the picture in a power point presentation he presented 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 Hawai`i?” — 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 Hawai`i, 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 state’s Pesticide Branch, 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.

“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. Risk assessments in Eisemann and Swift calculated that a 55 kilogram (120) pound pregnant woman or a 10 kilogram (22 pound) child would need to eat less than 1/2 pound per day (0.37 and 0.29 pounds respectively) over several days to cause effects observed in maternal rats. Liver lovers with an opportunity to indulge in wild pig liver pate would be able to easily consume this amount. Bon appetit!”

Boesch extended his concern about the inadvertent human consumption of diphacinone via contaminated wild-caught food to aerial rodenticide applications on offshore islets to control rats. In 2007, the state sought permits to do a diphacinone broadcast on Mokapu, a rock peak off the Moloka`i coast. When the project was first proposed, diphacinone was not allowed to be applied directly to water, areas where surface water is present, or intertidal areas below the mean high water mark, and the DOA refused to issue a permit to aerially broadcast diphacinone baits. The EPA, however, removed its restriction regarding applications in water in December 2007, and the project proceeded in February 2008.

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

Less than a year later, nearly four tons of diphacinone were aerially applied to Lehua over the course of two trips. Boesch stated in his paper that “tons” of dead fish and a juvenile whale reportedly washed up on Ni`ihau within days. Within weeks, another juvenile whale washed up in Kekaha, Kaua`i, although no diphacinone was detected in tissue samples taken.

Boesch points out that in all three cases — Keauhou, Mokapu, and Lehua — diphacinone bait was applied in amounts that exceeded the maximum amount specified by its label. What’s more, he argues that the tests used to detect diphacinone residues in the tissues of non-target species “are unable to detect values that result in harm and federal agencies have sought and obtained approvals to remove label statements critical to protect marine ecosystems from the EPA, making their rat eradication program largely unenforceable.”

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

“Unless laws are amended and [DOA] resources retained, Hawai`i’s capacity to regulate pesticides will [be] significantly impacted and [the state] will not be able to review and investigate issues critical to protecting human health and the environment and to keep collateral damage to a minimum,” he wrote.

Post Mortem

Seven months after the baits were dropped on Lehua, rats were seen on the island. The Research Corporation of the University hired New Zealand’s Landcare Research to conduct a review of the project for the Department of Land and Natural Resources. In their January 2011 final report, Landcare’s John Parkes and Penny Fisher identified several possible reasons why the project failed and also dismissed the possibility that the diphacinone bait had anything to do with the Ni`ihau fish kill or the humpback whale deaths.

They noted that no independent quality assurance of the diphacinone bait had been done, that coverage was constrained by the DOA’s instruction that no bait fall into the sea or within 30 meters of it, and that the bait was applied after a rainfall event in December “that triggered a flush of green vegetation with more abundant natural food that might have been more palatable than the cereal baits.”

The decision to bait after rain and the timing of the DOA’s regulatory conditions, in particular, increased the risk of failure, they wrote, adding that the permit’s expiration date — March 1, 2009 — also made it impossible for project managers to reapply bait in response to evidence of surviving rats, since the rats weren’t seen until August.

Ground-based rat control methods may have been permitted, but funding issues and regulatory concerns over the Ni`ihau fish deaths confounded any further action, they wrote. “Given the difficulties in detecting survivors at an early stage, a precautionary rather than reactive application might have been best, if it met the EPA label requirements for evidence of survival,” they wrote.

With regard to the fish deaths, they noted that evidence of a toxin from a freshwater blue-green algae was detected in the stomachs of some fish, giving “a little weight” to the possibility that the deaths were due to land-based runoff. No diphacinone residues were detected in any of the fish tested — dead or alive — 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,” they wrote.

“While various agencies undertook appropriate investigations to confirm whether diphacinone was involved and identify other potential causes of the fish mortality, their response (on 3 June) was outpaced by media and internet coverage, and by alarmist presentations” – here, they cite Boesch’s power point presentation at the western region pesticides meeting – “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,” they wrote.

In their recommendations, they called for studies to address concerns about the risk of diphacinone baits to marine fish.

“We do not think this is a high risk but regulators and the public need to be convinced. It is hard to see how one would do similar tests on cetaceans or pinnipeds, but common sense suggests exposure is highly unlikely and thus the risks low,” they wrote.

Robin Baird, a Hawai`i 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 draft EA that female humpbacks don’t feed in Hawai`i.

Screenshot 2017-04-03 09.50.25

Marine Impacts

The DLNR is intent on eradicating rats from Lehua, and in its draft EA, it stresses the need for the next eradication effort to be unrestricted by a coastal buffer requirement.

“Improved effectiveness of bait distribution to all rats on Lehua will be achieved by not excluding areas adjacent to coastlines for bait application, thus ensuring a uniform and complete distribution of bait in shoreline areas used by rats,” it states.

To assess the potential impacts to marine life should any bait fall into the water, the DLNR contracted Island Conservation to conduct a test run of another rodenticide drop in 2015. The trial used inert bait pellets similar to those to be used in an actual eradication. Pellets were tossed in the water while a diver watched how fish responded.

“During this trial, the number of fish that contacted and consumed bait was higher than that found in a similar survey conducted by USFWS surveys in 2008. It should be noted that the bait application rate for the 2015 survey was extremely high and would not be needed to eradicate rats from Lehua. Thus, this study may be viewed as a ‘worst case’ scenario to determine the species that may interact with bait pellets should they enter the marine environment in large quantities (e.g. bait spill),” the draft EA states.

Studies done so far have shown that some fish may eat diphacinone bait, while others won’t. “[S]ome fish species are able and will behaviorally avoid bait containing diphacinone, diminishing the potential for primary exposure,” the draft EA states.

It continues, “In the unlikely event of fish contamination by diphacinone, recent studies using three fish species indicate that they are amongst the least sensitive animals to the effects of diphacinone.”

Brodifacoum contamination, however, is possible. Residues of the toxin were found in fish after bait was applied to Palmyra Atoll, including residues in mullet found dead nearshore, the EA states, adding that, the impact was believed to be inconsequential at a population level.

The EA does not delve into the possible risks to any and all cetacean species found in waters surrounding Lehua. It only comments on the dead humpback whale calves from 2009, noting that they feed exclusively on milk and would have had “no possible contamination pathway by diphacinone.”

Baird told Environment Hawai`i 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. Since fishes are a common prey item to monk seals, there is a theoretical risk of brodifacoum moving through the marine food web, but the potential is very low. Calculations of risk have been made based on the residues in fish after the Palmyra rat eradication, and these pose a very conservative assessment of possible risk.”

To minimize the amount of bait falling into the water, the hoppers used to distribute the bait have a deflector that “spreads bait out to only one side, in an approximately 120-degree pattern,” the EA states, adding that bait pellets would also not be applied in high winds (greater than 35 mph) or when heavy rains are forecast within a few days of the application.

Should any bait fall into the ocean, the EA states, it would quickly dissolve.

“The total amount of diphacinone at 50 mg/kg per bait drop will be a maximum of 232.5g per drop. As a demonstration of low solubility, if all of the bait were dropped into the ocean, both brodifacoum and diphacinone would dissolve into the ocean and would be below the detection limit of analytical chemistry (0.003ug/l) in a volume of water the size of a football field 11 feet deep.

“Ocean currents would quickly dilute the chemicals to vanishingly small concentrations.

“Studies conducted after a rodent eradication in Anacapa island reported bait pellets were completely dissolved in seawater within five hours, which is similar to results reported from Kapiti Island, New Zealand,” it states.

— Teresa Dawson

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