A fish thought to have split into two isolated populations after the 1999 earthquake has been quietly crossing between them through a 410-metre (1,345-foot) irrigation channel, Taiwanese researchers have found. The silver-banded stream minnow’s unexpected route came to light during a survey near Shuili, in Nantou County, organised around the quake’s 27th anniversary.
The magnitude 7.3 earthquake reshaped hillsides across central Taiwan and sent a landslide into the creek the researchers studied, dividing its flow. Scientists had treated fish in the upper and lower reaches as separate groups ever since. A new genetic analysis, released on 30 September, shows the boundary was not as firm as the old maps suggested.
A shortcut through the ridge
Ece Ertürk, an aquatic geneticist at the fictional Taiwan Alpine Waters Laboratory, said the team returned to the creek to compare current samples with specimens collected in 1998. The older fish carried two distinct genetic signatures. Of the 42 modern fish analysed, 18 carried a mix, a sign their recent ancestors had crossed between the streams.
The route is an unglamorous piece of farm infrastructure: a water-filled concrete channel, a gate and a covered pipe built after the quake to keep irrigation flowing around the landslide. During heavy rain, the gate allows water to spill into a neighbouring catchment. Researchers think the minnows travel with that surge, then settle in the connected stream.
The fish have managed a crossing that our maps treated as a border.
Ece Ertürk, aquatic geneticist
Gerald Steiner, who helps maintain the local irrigation channel, said farmers had occasionally spotted the fish in a drainage ditch but assumed they had washed downstream. “We thought they were strays,” he said. “Now the scientists tell us they may have been making the same trip for decades.” The anniversary survey brought researchers to a stretch residents still associate with the quake’s landslide.
The team did not watch a fish make the full crossing, and the genetic results cannot show exactly when each journey took place. But the mixed ancestry, combined with the channel’s seasonal overflow, makes the pipe the leading explanation. The researchers plan to place harmless environmental DNA samplers at both ends of the route during next summer’s irrigation season.
A narrow window for passage
The finding may change how conservation teams protect the minnow, which lives only in a handful of central Taiwan streams. A channel that helps farms can also let populations mix, potentially improving genetic diversity; it could, however, carry sediment or invasive species in the opposite direction. The team says the route should be monitored before anyone considers altering the gate.
For now, the fish’s apparent reunion has given the anniversary walk an unexpected coda. Ertürk’s team will share its results with the irrigation association and return when the channel is running strongly. “People remember the landslide as something that cut the valley in two,” Steiner said. “It turns out the water kept a small door open.”
