Biology Reference
In-Depth Information
I
NTRODUCTION
There are two cetaceans endemic to the Yangtze River, the baiji or Yangtze River
dolphin (
Lipotes vexillifer
) and Yangtze finless porpoise (
Neophocaena phocaenoides
asiaeorientalis
). Both cetaceans occur in the middle and lower reaches of the river and two
appended lakes (Poyang and Dongting), China (Figure 1). As a mammal species at the top of
food chain, their survival heavily depends on habitat stability and food resource availability.
However, the Yangtze River, as the third largest river in the world and so called ―golden
channel of the country‖ in China, has been heavily used and explored by all kinds of human
activities which have led to the likely extinction of the baiji (Turvey et al., 2007).
Additionally, the Yangtze finless porpoise is now listed in the Second Order of Protected
Animals in China and has also been listed as an endangered population in the IUCN Red Data
Book since 1996 (Baillie & Groombridge, 1996).
A
BUNDANCE AND
D
ISTRIBUTION
Baiji
Baiji once occurred in the Qiantang River but disappeared in the 1950s (Zhou et al.,
1977) (Figure 1). As a member of the true river dolphins, a particularly rare group on this
planet, baiji was considered to be the most threatened cetacean (Reeves et al., 2003), and
probably the rarest animal within the category of large mammals (Dudgeon, 2005). This
species, as the sole representative of the Lipotidae family lineage diverging from other
cetacean more than 20 million years ago (mya) (Nikaido et al., 2001), has long been listed as
―Critically Endangered‖ by IUCN (Reeves et al., 2003) until very recently when it was
announced to be possibly extinct after an intensive range-wide survey concluded without a
single sighting in 2006 (Turvey et al., 2007). This would mean, although a few individuals
might still survive somewhere in the wild outside of detection limits, presumably, there is
only a slim chance of reversing its upcoming extinction. This will be the first aquatic mammal
species to be extinct since the demise of the Japanese Sea Lion (
Zalophus japonicus
) and the
West Indian Monk Seal (
Monachus tropicalis
) in the 1950s, as well the first cetacean species
to be extinguished as a result of human activity (Turvey et al., 2007).
There are occasional records on baiji in the historical Chinese literature dating back to
200 B.C. (~2,200 years ago, Guo, 200 B.C.). The baiji was well observed by the ancient
Chinese people and they could discriminate the precise differences between the baiji and
Yangtze finless porpoise that co-inhabited the same river. However, the international
scientific community didn't know this species until its scientific nomination by Miller in 1918
(Miller, 1918). No data was available on the abundance of baiji before the late 1970s, but we
speculate that baiji had at one time been quite abundant in the Yangtze River evidenced by its
description in ancient topics, e.g., Er-Ya (Guo, 200 B.C.) and Ru-Fan (Li, 1874). The first
systematic modern surveys of baiji were carried out during the late 1970s and early 1980s and
provided the first population abundance estimate. Approximately 300 individuals were
observed across their whole range (Lin et al., 1985; Chen & Hua, 1987, 1989) with about 100
individuals in
the downstream section (Zhou & Li, 1989) in 1980s. Then the subsequent
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