Endangered salmon thrive in restored creek

FLYING FISH: A team in November last year airlifted 240 salmon to the upper reaches of Sihjielan Creek, aiming to restore the species across the Dajia River

Taiwan’s endangered Formosan landlocked salmon has returned to Atayal ancestral lands, with wild spawning expected next month, the Shei-Pa National Park Headquarters said yesterday.

The landlocked salmon has re-established itself in the upper reaches of Sihjielan Creek (司界蘭溪) in central Taiwan, with a survey recording 117 adult fish after an aerial release last year, the headquarters said in a statement.

The survey found a visible survival rate of 48.75 percent and documented courtship and pairing behavior, indicating the fish are likely to spawn naturally in the wild as early as next month, it said.

Endangered Formosan landlocked salmon are pictured in an undated photograph.

Photo courtesy of Shei-Pa National Park Headquarters

The fish, now nearly two years old, have matured into healthy adults, with males and females displaying distinct secondary sexual characteristics.

According to Atayal oral history, Sihjielan Creek once supported a thriving wild population of Formosan landlocked salmon, but the fish eventually disappeared due to environmental changes and human development, the park headquarters said.

The headquarters described the creek as the final piece of the puzzle in restoring the species across its historic habitat in the Dajia River (大甲溪) basin.

The salmon has already been restored in Cijiawan Creek (七家灣溪), Hehuan Creek (合歡溪), Nanhu Creek (南湖溪) and Luoyewei Creek (羅葉尾溪), while several earlier reintroduction campaigns in Sihjielan Creek failed due to habitat degradation.

The creek’s habitat began to recover about a decade ago when floodwaters destroyed a downstream check dam. Natural erosion of the riverbed then recreated the deep pools and gravel beds the salmon need.

In September last year, the headquarters used a helicopter for the first time to airlift 240 salmon, then about 10 months old, to the upper reaches of Sihjielan Creek for release.

To assess the outcome, a research team set out from the Atayal village Sqoyaw (Huanshan, 環山部落) earlier this month, trekking 3.1km along the Jhihjayangshan (志佳陽大山) trail before descending into the river valley and wading 5.5km upstream for an overnight survey.

The team then snorkeled along a 600m section around the release site to record data on the fish, the headquarters said.

Because the fish were also seen beyond both ends of the surveyed section, suggesting some had dispersed farther upstream and downstream, the actual survival rate could exceed 50 percent, it said.

The headquarters said it would continue to monitor the emergence of juvenile salmon and the population’s resilience to flooding, with full annual survey results expected at the end of the year.