Biology Reference
In-Depth Information
Keywords
: Yangtze finless porpoise, Movement, Acoustic, Poyang Lake, Yangtze River.
I
NTRODUCTION
The Yangtze finless porpoise (
Neophocaena phocaenoides asiaeorientalis
), the only
freshwater subspecies of finless porpoise (
Neophocaena phocaenoides
), shares the same
habitat with the Yangtze River dolphin, locally called baiji (
Lipotes vexillifer
), which has
been declared to be functionally extinct (Turvey et al., 2007). Yangtze finless porpoises
historically distribute in the middle and lower reaches of the Yangtze River from Yichang to
Shanghai and its conjoint lakes, such as Poyang and Dongting (Figure 1). Due to human
activities such as fishing, transportation, pollution, and dam construction etc, the Yangtze
finless porpoise has been declining in population size and reducing its distribution range
sharply in the past thirty years (Wang et al., 2006), and has been listed as an endangered
species under the Red Data List criteria (C2b) by the International Union for the Conservation
of Nature and Natural Resources (IUCN) since 1996.
In November and December 2006, an intensive six-week visual and acoustic survey
(Yangtze Freshwater Dolphin Expedition 2006, YFDE 2006) to find baiji and to document
the status of the Yangtze finless porpoise was carried out by the Institute of Hydrobiology,
Chinese Academy of Sciences (IHB) and Baiji.org Foundation (Swiss organization) with
international collaborators (Turvey et al., 2007; Akamatsu et al., 2008b; Zhao et al., 2008).
The survey covered the entire historical distribution range of the porpoise in the main channel
of the Yangtze River and mouth area of Poyang Lake. The results indicated that the porpoise
population in the main channel of the Yangtze River was approximately 1,200 (Zhao et al.,
2008), which was less than half of its population size in the early 1990s (Zhang et al., 1993).
Fragmentation of habitat and apparent long-distance (over 100 km) gap, where no animals
were detected, was also observed (Zhao et al., 2008). Also, mtDNA haplotype analysis
indicated that differences in genetic structure were present among populations of the Yangtze
finless porpoise (Zheng et al., 2005).
The mouth area of Poyang Lake, a channel connecting the lake and the main stem of the
Yangtze River, is a traditional ―hot spot‖ area for porpoises. Historically, large groups of
porpoises could be frequently observed in this area moving back and forth between the
Yangtze River and Poyang Lake (Zhang et al., 1993; Wei et al., 2002). Unfortunately, the
mouth area is also a geographical ―bottleneck‖ between the Poyang Lake and Yangtze River.
It is not only a heavy shipping traffic channel, but also an appropriate site to construct bridges
for terrestrial traffic. In the two recent decades, along with economic development, human
activities, such as fishery, transportation, and bridge constructions etc, have been remarkably
expanding in the mouth area. Since sand-digging activity was initiated in Poyang Lake after
1998, there have been hundreds of additional sand- transporting ships passing through the
mouth area day and night. In addition, two bridges, one for a highway and the second for a
railway cross this channel, approximately 3 km from each other (Figure 1), were recently
constructed (2000 and 2008).
Human activities have caused a serious threat on porpoise survival in this area. By visual
observation, Wei et al. (2002) found that the group size of animals in this area had been
decreasing continually from 1989 to 1999, and the ―back and forth‖ movement of animals
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