Wildlife officials still have not figured out why several pilot whales beached themselves on Kauai.

Five whales died during a mass stranding along Kalapaki Beach on Oct. 13. Two washed onto the beach while three more were found floating in Nawiliwili Harbor.

They did, however, rule out one possibility: rodenticide that was previously dropped on nearby Lehua Island to control its invasive rat population.

Frozen liver samples from the whales, taken during post-stranding necropsies immediately after the mammals were moved off the beach, were analyzed by the U.S. Department of Agriculture’s National Wildlife Research Center.

According to a report released Tuesday, no “observed concentration of Diphacinone” was detected in any of the 15 samples.

The Hawaii Department of Land and Natural Resources, NOAA’s Pacific Islands Regional Office, and the University of Hawaii cooperated in the necropsies conducted on the pilot whales and so far have been unable to determine a conclusive cause of death.

Additional testing continues.

Officials say so far, no rats have been found on Lehua Island since the final drop of rodenticide was applied in September.