Two months after dead birds and fish were discovered on Lehua Island, there’s still no indication of what killed them.
The Hawaii Department of Land and Natural Resources says preliminary results are inconclusive because the samples that were taken were too decomposed.
The state dropped three rounds of bait pellets containing diphacinone, a type of rodenticide, on the island off Niihau to kill invasive rats.
After the second application was dropped, pictures and video of dead fish and green powder surfaced on social media, prompting project partners to deploy teams to investigate.
They collected 45 dead fish, which appear to be mullets, and two dead birds, which appear to be juvenile brown boobies, from the island’s north, or crater end.
However, officials say the samples were in a “severely degraded condition,” making it impossible to determine whether the mullet-type fish were affected by diphacinone or died due to other factors associated with being trapped in tide pools; such as high temperature or limited oxygen.
It is also not clear whether or not the fish were intentionally placed in a tide pool on the northern side of Lehua Island, officials say.
Preliminary results from USDA’s visual examination of the specimens show external and internal signs of UV fluorescence from the pyranine biomarker incorporated into the diphacinone bait. However, because the internal organs such as livers and stomachs were decomposed, the results are inconclusive as to whether the fluorescence resulted from consumption of the bait or immersion in the tide pool where bait pellets dissolved.
Chemical analysis of the degraded tissues will likely be unable to determine if the fish died from ingesting diphacinone bait or absorbed diphacinone after dying of other causes.
A final report regarding the mullet-type fish will be included in the results of the full environmental monitoring analysis of samples collected before and after bait application, including samples of multiple fish species, seawater, soil, crabs, and opihi.