Abstract
The population of finless porpoises (Neophocaena phocaenoides) that inhabits China’s Yangtze River is unique. All other known populations of the species are distributed principally in marine waters. This population is also one of the few geographical populations of cetaceans (whales, dolphins, and porpoises) listed as Endangered in the 1996 IUCN Red List of Threatened Animals. Chinese scientists report that Yangtze finless porpoises are rapidly declining and that, in response, officials within China wish to stock “semi-natural reserves” and other facilities with porpoises. This approach to conservation was adopted several years ago with the explicit objective of preventing the extinction of baiji (Lipotes vexillifer). Although the baiji rescue effort has been unsuccessful so far, it appears that the same approach is now being taken to conserve the finless porpoise, with no rigorous advance consideration of its appropriateness.
A workshop was convened at Ocean Park, Hong Kong, in September 1997 to review information on Yangtze River finless porpoises and develop recommendations concerning their conservation. Participants included experts from China, Japan, Hong Kong, Taiwan, the United States, and Canada. Planning and execution were done jointly by Ocean Park Conservation Foundation and the IUCN/SSC Cetacean Specialist Group.
Wang Ding, of the Wuhan Institute of Hydrobiology (WIH), summarized recent research and management activities in the upper reaches of the Yangtze. A population estimate of 2,700 porpoises was made, referring to the period 1978-91. More recent surveys provided indices pointing to a dramatic decline in abundance since then. Thirty-six finless porpoises have been removed from the Yangtze and placed in the Shishou semi-natural reserve since March 1990. Nine porpoises have been born in the reserve, including one that is known to have been conceived there. Losses, due mainly to escape and accidental killing, have resulted in a current population of five porpoises in the reserve. Two outstanding problems with the reserve were noted: (1) a barrier to prevent animals from escaping during the flood season has not been completed, and (2) fishing within the reserve continues to pose a threat to the porpoises and their food supply. Additional porpoises have been brought into captivity at the WIH, where two animals presently reside.
Zhou Kaiya, of Nanjing Normal University, summarized work on a life table and population dynamics of finless porpoises in Chinese waters, as well as recent survey work in the lower reaches of the Yangtze. Although some concerns were expressed about possible bias from the ways specimens were obtained, the life table analyses generally reinforce the conclusion from surveys that there is a serious conservation problem with finless porpoises, not only in the Yangtze River, but also in coastal marine waters. Surveys in 1990-92 suggested a total porpoise population of about 700 porpoises in a 421km segment of the lower reaches. Results of these surveys also support the hypothesis that porpoises occur in greater abundance and in larger groups in river reaches characterized by numerous bends and sandbars, relatively slow water flow, rich fish resources, and relatively little vessel traffic.
Threats to finless porpoises in the Yangtze River include incidental mortality from entanglement in passive fishing gear, electric fishing, collisions with powered vessels, and exposure to explosives used for harbor construction. Much of their habitat has been severely degraded, due to the damming of Yangtze tributaries and the intensive use of the river as a transportation corridor. The effects of pollution and reduced availability of prey species are not well documented, but they represent serious additional concerns. Numerous topics were formally discussed by the group before formulating conclusions and recommendations.The workshop’s principal conclusions were:
1. The finless porpoise population in the Yangtze River is likely to continue declining unless serious efforts are made to protect the animals and their habitat (including prey resources).
2. The ultimate goal of conservation efforts must be to maintain a viable wild population of porpoises in the river, and any ex-situ conservation strategy (e.g. establishment of “semi-natural reserves,” maintenance of porpoises in captivity) can only be justified if it contributes to that goal.
3. Even more important than creating new “natural reserves” or expanding existing ones is the need to educate people about, and strictly enforce, regulations concerning the use of destructive fishing gear or methods.
4. A deliberate, step-by-step approach should be taken in evaluating any proposal for ex-situ conservation of Yangtze finless porpoises. In the specific case of Shishou semi-natural reserve, it should be acknowledged that a porpoise “population” already exists there. Thus, an initial requirement is that all harmful fishing be eliminated and the barrier fence be completed to improve the safety and security of those five animals. A critical review of available information is needed to provide advice on the required size and composition of a founding stock of finless porpoises. Water quality and sediment in the reserve need to be rigorously evaluated and monitored on an ongoing basis. A program of studying the animals presently in the reserve should be initiated, including marking (e.g. freeze-branding) and a sampling regimen of some kind. These steps should be taken prior to any consideration of further captures to stock the Shishou reserve.
5. The Tongling facility is best used, for the present, as a rehabilitation center for sick or injured porpoises (and dolphins) rather than being stocked with additional deliberately caught animals.
6. Like the five animals already present in Shishou reserve, the two animals already in captivity at the WIH
constitute a small existing captive “population.” Strenuous efforts should be made to improve the quality of their environment and to advance knowledge by observing and experimenting with these porpoises. Collaboration in these endeavours with experts from Hong Kong, Japan, and elsewhere is highly desirable.
7. Among the types of additional research that are needed to support conservation efforts are: tracking and marking studies in the wild and possibly also inside the Shishou Reserve; site‘specific studies in key areas to investigate aspects such as the nature of threats, local movements by groups or individuals, and habitat preferences; and studies of genetics and contaminant levels using tissues from salvaged carcasses or from biopsies (e. g. skin scrapings) from live animals.
8. A scientific presence should be established and maintained in and near the Xin Luo Natural Reserve for baiji, with at least two primary objectives: (1) to provide a means of evaluating the effectiveness of protective measures and (2) to obtain information that can be used to guide management decisions in the future (e. g. changes in the reserve boundaries).