Taiwan’s marine biodiversity is shaped by its position astride the Kuroshio Current, the Pacific’s second-largest warm-water current after the Gulf Stream, which sweeps nutrient-rich water northward along the island’s eastern coast and draws an exceptional diversity of marine life.

Whale and dolphin watching is most productive along the east coast. Taiwan has recorded 31 species of cetaceans — over one third of all species known worldwide — and sighting rates on east-coast tours typically run between 80 and 90 per cent in the summer. The principal departure points are Hualien and Chenggong Harbour (Taitung) in the south, and Wushi Harbour near Yilan in the north, from which tours also circle Guishan Island (Turtle Island). Commonly sighted species include Risso’s Dolphins, Spinner Dolphins, Bottlenose Dolphins, Pantropical Spotted Dolphins, and Fraser’s Dolphins. Sperm Whales, Pilot Whales, and Killer Whales are seen less frequently. Peak season runs from April to October, with May through September offering the calmest seas and highest cetacean activity.

Sea turtles are a highlight of Xiaoliuqiu（小琉球, Liuqiu Island）, a small coral island accessible by ferry from Donggang near Pingtung. Green Sea Turtles are resident year-round in the reef systems just off the island’s beaches and can be observed snorkelling in very shallow water — sometimes from the shoreline itself. The experience is widely described as among the most accessible wild sea turtle encounters in Asia.

Coral reefs are most intact around Taiwan’s offshore islands. Green Island （綠島, Ludao） off the Taitung coast and Orchid Island （蘭嶼, Lanyu） to the south are the standout reef diving destinations on the main island circuit; the Penghu Archipelago and Kenting’s outer waters also support significant reef ecosystems. Taiwan forms part of the Southern Japan, Taiwan, and Southern China coral reef hotspot, a globally recognised centre of Indo-Pacific marine biodiversity.