Paddlefish
Paddlefish (family Polyodontidae) are basal Chondrostean ray-finned fish.[2] They have been referred to as "primitive fish" because they have evolved with few morphological changes since the earliest fossil records of the Early Cretaceous, 120 to 125 million years ago.[3] Polyodontids are almost exclusively North American and Chinese, both extant and in the fossil record[4]
There are six known species: four extinct species known only from fossil remains (three from western North America, one from China), one extant species, the American paddlefish (Polyodon spathula) which is native to the Mississippi River basin in the U.S., and the Chinese paddlefish (Psephurus gladius), reported as likely extinct in 2019.[5] The species was last sighted in 2003 in the Yangtze River Basin in China.[6][7] Chinese paddlefish are also commonly referred to as "Chinese swordfish", or "elephant fish".[8] The earliest known species is Protopsephurus from the Early Cretaceous (Barremian) of China.
Paddlefish populations have declined dramatically throughout their historic range as a result of overfishing, pollution, and the encroachment of human development, including the construction of dams that have blocked their seasonal upward migration to ancestral spawning grounds.[9] Other detrimental effects include alterations of rivers which have changed natural flows resulting in the loss of spawning habitat and nursery areas
Over the past half century, paddlefish populations have been on the decline. Attributable causes are overfishing, pollution, and the encroachment of human development, including the construction of dams which block their seasonal upward migration to ancestral spawning grounds. Other detrimental effects include alterations of rivers which have changed the natural flow, and resulted in the loss of spawning habitat and nursery areas. American paddlefish have been extirpated from much of their Northern peripheral range, including the Great Lakes and Canada, New York, Maryland and Pennsylvania. There is growing concern about their populations in other states.
The Chinese paddlefish is considered anadromous with upstream migration, however little is known about their migration habits and population structure. They are endemic to the Yangtze River Basin in China where they lived primarily in the broad surfaced main stem rivers and shoal zones along the East China Sea.[citation needed] Research suggests they preferred to navigate the middle and lower layers of the water column, and occasionally swam into large lakes.[7] There have been no sightings of Chinese paddlefish since 2003, and was reported as extinct in 2019.[5] Past attempts of artificial propagation for restoration purposes have failed because of difficulties encountered in keeping captive fish alive.[20]
American paddlefish are native to the Mississippi River basin from New York to Montana and south to the Gulf of Mexico.[21] They have been found in several Gulf Slope drainages in medium to large rivers with long, deep sluggish pools, as well as in backwater lakes and bayous.[3] In Texas, paddlefish occurred historically in the Angelina River, Big Cypress Bayou, Neches River, Red River tributaries, Sabine River, San Jacinto River, Sulphur River, and Trinity River.[21] Their historical range also included occurrences in Canada in Lake Huron and Lake Helen, and in 26–27 states in the United States. The Ontario Ministry of Natural Resources listed the paddlefish as extirpated from Ontario, Canada under their Endangered Species Act.[22] The IUCN Red List lists the Canadian populations of paddlefish as extirpated, noting there have been no Canadian records since the early 1900s and distribution in Canada was highly peripheral. As a species, the American paddlefish is classified as vulnerable (VU) on the IUCN Red List, and its international trade has been restricted since June 1992 under Appendix II of the Convention of International Trade in Endangered Species of Wild Flora and Fauna, or CITES