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"Professor Ding says based on anecdotal evidence, he remains confident the dolphins are still out there.
"I'm pretty much sure there are a few of them left somewhere in the Yangtze River," he said.
"I keep receiving reports from fishermen, they say they saw a couple of baiji somewhere, sometime.
"But unfortunately most of them cannot be confirmed, and the Yangtze River is a big river, so I really cannot say the Baiji is already gone, there is no baiji left at all, I really cannot say that."
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Still hope for the Chinese baiji, be it anecdotal and not scientifically verified. If it survives it is in the very low numbers that make direct observations highly unlikely. The most serious threat to their continued existence is human exploitation of the Yang Ze river basin and pollution. Only if the Chinese authorities seriously implement a long term recovery plan that underpins the threats to the baiji and its environment does it stand a chance of surviving the 21st century. Remember however that even the aquatic protected area instituted for them did not safeguard a future for them!
As to your remark that a species has to go unrecorded for 50 years before it may be declared extinct is untrue. F.i. the Arabian oryx was officially declared extinct in 1976 when continuous surveys failed to find any survivors from the last Omani-Yemeni border herds. Since then it has been listed for quite a while on IUCN's Red List as EXT. Interestingly, this refutes the claim that no large vertebrate animal has gone extinct on earth in the last 50 years. It is simply hogwash and sadly .. very sadly the Oryx leucoryx was not the only one!
Fortunately, it does not mean a species may not resurface. This goes in particular for the tropical rainforests that still harbour many secrets (e.g. Vietnam, Cambodia, Laos, Congo, Gabon, Brasil, Ecuador-Bolivia-Peru). Sometimes even new species may be discovered (Madagascar, Vietnam, Congo are recent examples).
And even the Tasmanian wolf might still be around (continuous infrequent anecdotal records in Tasmania, quite reliable reports from SE- Oz and PNG)! Maybe we could start a new thread on this ...... I don't know!!!