- Final Rule (83 FR 21182, May 9, 2018)
- Proposed Rule (82 FR 28802, June 26, 2017)
- 90-day Finding (81 FR 29515, May 12, 2016)
The 2018 status review report conducted on a petition to list the Taiwanese humpback dolphin, a…
Sousa chinensis taiwanensis
The Taiwanese humpback dolphin is a subspecies of the Indo-Pacific humpback dolphin that is only found in a small, narrow stretch of estuarine water off the western coast of Taiwan. This subspecies was first described in 2002 but did not receive formal recognition until 2016. The population is small with fewer than 100 individuals remaining. It also has late maturity, slow reproductive rate, long calving intervals, and long periods of female-calf association.
The main threats to the Taiwanese humpback dolphin include bycatch and entanglement in fisheries and habitat destruction and degradation due to coastal development. In 2018, NOAA Fisheries listed the dolphin as endangered under the Endangered Species Act.
In general, the Indo-Pacific humpback dolphin is easily distinguished from other dolphin species in its range. It has a robust body, a long distinct beak, a short dorsal fin situated on a wide dorsal hump, and round-tipped, broad flippers and tail.
The Taiwanese humpback dolphin subspecies has a unique appearance. Young dolphins appear dark grey with no or few light-colored spots. As adults, the Taiwanese humpback dolphin looks mostly white and appears pinkish with spots on the dorsal fin that remain throughout their lives.
The Taiwanese humpback dolphin is considered a generalist and opportunistic feeder that primarily eats fish. Although information on the subspecies’ feeding behavior and diet is limited, their diet is likely predominantly estuarine fish and occasionally cephalopods and crustaceans.
The Taiwanese humpback dolphin has a very restricted range as it lives in a very narrow strip of shallow, estuarine water off the coast of central western Taiwan with no evidence of seasonal movements. The total distribution of the dolphin covers approximately 466 square miles, but its core distribution encompasses only approximately 318 square miles of coastal waters. The population is largely concentrated between the Tongshiao River estuary and Taixi, which encompasses the estuaries of the Dadu and Jhushuei rivers, the two largest river systems in western Taiwan. This subspecies prefers shallow water of less than 65 feet deep and has never been observed in waters deeper than 98 feet.
Information on the Taiwanese humpback dolphin’s life history is limited. The dolphin likely lives to approximately 40 years of age based on studies of closely related populations. Pregnancy lasts 10 to 12 months and weaning may take up to 2 years. There are strong female-calf relationships that may last 3 to 4 years. Births occur throughout the year but decrease in late summer and through mid-winter with the majority of the estimated births occurring in spring and summer. Average calving intervals (the time between the estimated birth months of two successive calves) is approximately 3 years.
The Taiwanese humpback dolphin is facing the combined effects of fisheries impacts and habitat destruction and degradation. Entanglements due to interactions with fishing gear are likely the most serious and immediate threat to the dolphin, which cause serious injury and mortality. Ongoing coastal development in Taiwan, including land reclamation activities, fresh water diversion, and pollution are destroying and degrading the dolphin’s limited habitat.
The Taiwanese humpback dolphin is a critically endangered marine mammal with fewer than 100 individuals remaining.
Dolphins, like other marine mammals, may become bycatch in fisheries. Some species of tuna are known to aggregate beneath schools of certain dolphin stocks. In some parts of the world, this close association led to the fishing practice of encircling a dolphin school to capture the tuna concentrated below. The Dolphin Protection Consumer Information Act established a national tuna tracking program to ensure that tuna imported into the United States meets certain requirements to ensure the safety of dolphins during tuna fishing operations.
Under the Marine Mammal Protection Act, an unusual mortality event (UME) is defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response." To understand the health of marine mammal populations, scientists study unusual mortality events.
In 2016, NOAA Fisheries received a petition to list the Taiwanese humpback dolphin as threatened or endangered under the Endangered Species Act. In our 90-day finding, we concluded that the petitioned action may be warranted. After completing a status review, we proposed to list the subspecies as endangered and requested comments from the public. In May 2018, NOAA Fisheries listed the Taiwanese humpback dolphin as endangered under the Endangered Species Act.