According to NOAA, almost half of all Baiji dolphin deaths can be blamed on rolling hooks, even though this fishing method is banned. This technique entails dragging long fishing lines, along the bottom of the river, with unbaited hooks (called rolling hooks) that are intended for bottom-feeding fish. At least 22 dolphins were killed incidentally by this method between 1973 and 1985, according to the International Union for Conservation of Nature and Natural Resources (IUCN). Other dolphins were observed to have wounds and scars inflicted by the hooks.
As ships and boats became larger and more commercially active in the Yangtze river in the late 80s and early 90s, noise pollution interfered with the dolphin's radar, causing auditory "blindness." This condition prevented them from detecting boats, which caused them to collide with propellers and resulted in many deaths. Explosives used to widen river channels for fishing could have caused deaths as well, speculated the IUCN.
Large quantities of industrial and agricultural waste, up to 40 percent of China's output, caused a significant increase in the Yangtze's water pollution levels and killed much of the dolphins' available prey. Also, the change in the Yangtze habitat caused by concrete reinforcements to river walls, dams and dredged riverbeds interrupted the dolphins' upstream movements into tributaries, dams and lakes, reducing both fish productivity and the dolphins' access to fish, according to Sixth Extinction.
Electric fishing, despite being recognized as an immediate threat to the species' survival in the early 2000s, still was practiced in the Yangtze river illegally up until the dolphin's extinction. This fishing method, in which an underwater device is used to stun aquatic animals, kills any organisms, including what was once the dolphin's prey. As much as 40 percent of dolphin deaths may be attributed to this illegal fishing method, the NOAA reports.