Sharks are a problem for the Hawaiian monk seal, as are commercial fishing nets. Many sick and dying seals were observed in the first half of 1978. Samples of their livers were taken from some of the seals. The samples indicated that there was a poison called ciguatoxin, a toxin produced by protozoan that is concentrated through the food chain making the flesh of the affected fish highly toxic to mammals. Ciguatoxin outbreaks occur when a coral reef has been disturbed.
Pollution poses threat to seals because it concentrates in body fat which seals have a lot of.
Another danger to the seals is that they were hunted by humans while they were basking on the beaches. They were usually clubbed to death for their fur. But that was in the past. The sealing Brig Aiona took what was thought to be the last of the Hawaiian Monk Seal population. Luckily, some managed to survive on islands that were hard to get to.