Fantail filefish populations ebb and flow over the years

When Craig and I moved to Hawaii in 1983, we saw so many fantail filefish, we thought the species, found only in Hawaii, might be the state fish. The 7-inch-long fantails were easy to see and not just because of their striking colors.

The little omnivores were everywhere, nibbling on coral, picking algae off rocks and grazing on dead things.

You didn’t even have to go snorkeling to see fantail filefish. They washed up on Hawaii beaches by the thousands, lying in bright lines of yellow, orange and blue.

A few years later they were gone — so gone that seeing one on the reef was a noteworthy event.

And now they’re back. Fantail filefish are once again a common sight on island reefs.

This boom and bust cycle is normal for fantail filefish, a fact we know because ancient Hawaiians noted the blooms, believing that when the fish, oili uwi­uwi, washed up on beaches, an alii, or chief, would die.

After the filefish dried, people burned them as fuel.

No one knows how often fantail filefish populations exploded in old Hawaii. The first recorded year of high abundance was 1903; the next, 1944. The mid-’50s had a flood of these fish, with another in 1975.

During my early years in Hawaii, the fantails flourished for years on end, starting in the Northwestern Hawaiian Islands in 1982, moving to the main islands in 1983 and lasting until 1987.

No one knows why filefish numbers fluctuate so extremely, but one guess is that it involves conditions offshore. A local researcher in the past observed that one year when Hawaii waters were cooler than normal, and the tuna catch was poor, the filefish population surged.

It’s possible, he speculated, that lower numbers of tuna resulted in a higher rate of filefish larval survival because in addition to fish and squid, tunas also eat animal plankton.

Filefish and triggerfish are similar in shape, and the two families are closely related. Members of both have one stout spine on their backs that the fish raise when threatened. Filefish get their name not from the spine, though, but from their sandpapery scales.

Fantails can rapidly change color to blend in with a background.

One quirk of this species is that two sometimes swim head to tail, sides nearly touching, while moving the back spines up and down and fanning their orange tails.

It’s common these days to see this odd pairing, a behavior that could be a flirtation or a claim to territory. Craig’s theory is that the fish are like dogs, sniffing each other to say hello. Only the fish know for sure.

Since the 1980s I’ve learned a lot about Hawaii’s fish. Now I know that when fantail filefish appear, I should get out there and enjoy them while they last.

Reach Susan Scott at www.susanscott.net.