Investigation Underway Regarding Lehua Island Fish and Bird Deaths

Aerial photographs of Lehua, rats, birds, and rodenticide application. PC: Hawai‘i DLNR.

After numerous social media posts, photos, and videos showing dead fish or birds that posters claim were killed by a rodenticide currently being used to eradicate non-native, damaging (invasive) rats from Lehua Island, the DLNR, Island Conservation, and other Lehua Island Restoration Project partners have deployed on-island monitoring teams to investigate.

Officials say the connection is unlikely, however, the project partners say they take any potential risks to non-target species and marine life extremely serious.

The deployed teams, which include both project staff and independent monitors from the US Department of Agriculture, are going to where a video was reportedly taken on the north/crater side of Lehua Island.

The team has confirmed and collected 45 dead fish which officials say appear to be mullets and two dead birds which appear to be juvenile Brown boobies. The teams say the samples do not show any immediate evidence of impact from diphacinone, the rodenticide used in the operation.

The deployed crew says mortalities of fish and seabirds occur regularly, and there are many other plausible causes for the deaths. Mortality among wild fish and bird populations is common so a correlation does not demonstrate causation.

The samples are under USDA chain-of-custody and will be processed to determine likely cause of death or presence of diphacinone. Partners are seeking an expedited assessment.

From the beginning of the operation last month, the teams have been monitoring the steep and rugged part of the island from a safe distance using binoculars from high vantage points that can be safely reach on foot. At first light on Wednesday, Sept. 6, a DLNR Division of Boating and Ocean Recreation vessel will depart from Kaua‘i with biologists from the DLNR Division of Aquatic Resources and other monitoring team members to get a closer look at the crater-side of Lehua. If any dead birds or fish are found, samples will be collected and sent to a laboratory for testing.

Officials say that monitoring teams have been on island throughout the entire operation and make daily trips to the accessible nearshore marine environment and tide pools on the south side of the island. There have been no observations of dead fish, birds, or other non-target species during the checks.

The teams stated that with any project of this nature, there are some inherent short-term risks, and Federal and State permits and regulations acknowledge that a negligible amount of bait will reach the marine waters. Project proponents have pursued this project only because they are convinced the small potential for short lived risks to non-targets species is far outweighed by the long-term conservation benefits of an invasive rat-free Lehua Island.

Lab studies have shown that fish reject bait containing diphacinone, the approved rodenticide being used in the restoration project. Furthermore, officials say fish are among the least likely animals to be affected by the rodenticide. What little bait drifts into water from the over-land application sinks to the sea floor and degrades quickly.

Diphacinone, being almost insoluble, scarcely dissolves in water and mostly remains in bait pellet fragments on the sea bottom. Diphacinone breaks down quickly in water when exposed to ultraviolet light (e.g. sunlight) — a likely fate for some drifted bait. Eventually, the rodenticide decomposes into carbon dioxide and water and intermediate compounds in its decomposition process are non-toxic.

In hundreds of similar projects, no documented impacts to marine mammals or corals have been documented, and invertebrates are not affected at all as they do not metabolize diphacinone. Therefore, regulators concluded that marine life will have little to no exposure to the negligible amount of rodenticide that drifts into the water.

A third and final additional applications of rodenticide is planned in the next few weeks depending on weather conditions.