Just over 100 years ago, Japanese scientist Oshima Masamitsu, writing in an obscure agricultural bulletin, revealed to the world the existence of a remarkable fish. Oncorhynchus formosanus, commonly called the Formosan landlocked salmon, isn’t the only salmon species in the world that never ventures to the sea. But, confined to a small corner of Taiwan’s mountainous interior, it’s both the world’s southernmost salmon species, and the only one found more than 1,700 m above sea level.
Scores of scientists have followed in Oshima’s footsteps and tried to find out more about this fish, which seldom grows longer than 40 cm, and which rarely lives more than four years. In recent decades, they’ve focused on identifying the causes of its decline and what measures might prevent its extinction. To better understand the fish’s movement patterns, salmon have been tagged with miniature radio transmitters.
Visitors interested in seeing the landlocked salmon and its habitat should spend a night or two in Wuling Farm, part of Shei-Pa National Park. Artificially hatched salmon (pictured here) swim in display tanks at the farm’s Taiwan Salmon Eco Centre. It’s by far the best place to see the species because access to its main habitat, Qijiawan Creek (pictured above), is carefully restricted.
Scientists believe that Oncorhynchus formosanus, which is listed by the International Union for Conservation of Nature and Natural Resources as a critically endangered species, owes its distinctiveness to a meteor impact about 780,000 years strike ago. That calamity not merely led to significant global cooling but also caused magnetic north and south to swap poles. Cooler seas and the likelihood that their magnetic navigation skills were confused probably led to Japanese salmon venturing further south than before.
Temperature, not geography, traps the salmon in the chilly mountain streams to which they retreated as the Earth and its oceans warmed. Its eggs cannot hatch if the water is warmer than 12 degrees C, and mature fish are vulnerable to fungi and bacteria if the temperature tops 17 degrees C. Conservation efforts therefore focus on keeping the Qijiawan Creek cool by planting trees to shade the waterway. The authorities have also curtailed agriculture in the area and demolished weirs which fragmented the population. These measures seem to have had some success yet the future of the species is far from certain.
Oncorhynchus formosanus isn’t the only fish species unique to Taiwan. In fact, 36 of the island’s 220 freshwater species are so-called endemics, meaning they’re found nowhere else on Earth. Among them are the Thickhead chub (Opsariichthys pachycephalus) and the Formosan river loach (Hemimyzon formosanus), both of which are far smaller than the landlocked salmon. In its waters as in its skies, Taiwan has an abundance of biological treasures!