Bioacoustics of Lipotes vexillifer

Status and Conservation. CITES Appendix I. Classified as Critically Endangered on The IUCN Red List (probably now extinct). The historical abundance of the Baiji is little known due to the relatively late attention the species received from conservation science and difficulties in applying standardized population assessment techniques in large floodplain rivers. In the late 1970s and early 1980s, based on sighting surveys, local scientists made educated guesses that only 300-400 Baijis remained in the Yangtze River. By the late 1980s and early 1990s, surveys suggested a population of ¢.100 individuals, declining to a maximal count of 13 dolphins recorded during a rangewide survey in 1997. Even though no time series of rigorous abundance estimates is available, the Baiji undoubtedly underwent a rapid decline from when surveys began in the late 1970s, and it almost certainly went extinct less than 100 years after the species was described scientifically. An exhaustive visual and acoustic survey for the Baiji in 2006 and an extensive interview survey in 2008 failed to find evidence of its continued existence. Pernicious fishery interactions were probably the primary cause of the species’ precipitous decline (particularly snagging on illegal bottom-set long lines with multiple hooks in the 1980s and possibly electrocution from illegal electrofishing starting in the 1990s); however, construction of extensive hydropower, flood control, and irrigation projects, resulting in extensive habitat loss in the Yangtze River system, were almost certainly contributing factors. Efforts to prevent extinction of the Baiji were hampered by a lack of consensus on whether or not it should be protected within a degraded Yangtze ecosystem or if an ex situ population should be established in one or more “semi-natural” reserves. Ultimately, an insufficient commitment was made to implement either approach, and the Baiji is presumed to be extinct. This represents a disproportionately large loss of evolutionary history because the Baija belongs to a monotypic family with no living sister taxon.