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study. Since the formation of this collaboration, the Institute of Hydrobiology, CAS and
Nanjing Normal College began to survey in the river (Zhang et al., 1993; Zhou et al., 1998b;
Wang et al., 1998, 2000; Xiao & Zhang, 2000, 2002; Yang et al., 2000; Wei et al., 2002).
Most of the earlier surveys were conducted by a single survey ship, or a single survey ship
with several small fishing boats, and no standard methods were applied. The first range-wide
estimate of finless porpoise abundance in the Yangtze River system (~2700 porpoises) was
based on many such kinds of small-scale surveys conducted between 1984 and 1991 (Zhang
et al., 1993). Thereafter, fragmentary surveys in different sections of the Yangtze River were
carried out by various researchers using essentially the same survey methods (Wang et al.,
1998, 2000; Zhou et al., 1998b; Yang et al., 2000; Yu et al., 2001). During 1997 to 1999, a
series of so-called ―Synchronous Surveys‖, one in each year, were conducted by the Ministry
of Agriculture and the Institute of Hydrobiology, CAS. For those surveys, the historic
distribution ranges of baiji and the Yangtze finless porpoise within the middle and lower
Yangtze River from Yichang to Shanghai, Poyang and Dongting Lake, and their main
tributaries were divided into 21 sections (lengths varied from 50 - 200 km). Two large boats
(~30 m long) simultaneously searched each section for one week during November of each
year. Preliminarily analyses on the data collected showed that there were approximately 2,000
animals left in the river at the time the surveys were conducted (D. Wang, unpublished data;
for the design of the surveys, please see Zhang et al., 2003). In November and December of
2006, a systematic survey was conducted in the entire current range of the population in the
main stem of the Yangtze River (except for lakes Poyang and Dongting) by using a modified
standard Line-transect Survey method which was pre-designed based on the results of a pilot
survey between Wuhan and Yueyang (Figure 1) (Zhao et al., 2008). Both visual and acoustic
methods were utilized in the survey (Akamatsu et al., 2008; Zhao et al., 2008) and experts and
researchers from the United States, United Kingdom, Germany, Japan, Switzerland, Canada
and China participated as part of an international collaborative effort. The findings of this
extensive survey indicated that the finless porpoise population within the Yangtze's main
stem is approximately 1,000 to 1,200 individuals. If the two lakes are included, the overall
estimate of the population increases to approximately 1,800 (Zhao et al., 2008). This means
that the current population size of the porpoise in the main stem of the river is less than half
of the estimate (2,550) from surveys completed between 1984 and 1991 (Zhang et al., 1993),
and it implies an annual rate of decline of at least 5% for the whole population in the main
stem of the river (Zhao et al., 2008).
The Yangtze finless porpoise is now primarily restricted to the main river channel and its
two largest appended lakes (Poyang and Dongting). It had occasionally occurred in some
large adjacent tributaries of the river and lakes, but now has been extirpated from most of
these areas (Zhang et al., 1993; Yang et al., 2000; Xiao & Zhang, 2002). Of the six extant
species of porpoise (Phocoenidae), this is the only population found in fresh water (Gao &
Zhou, 1995). The amount of river and lake habitat available to this subspecies is relatively
small compared to that available to marine populations of finless porpoises, which occur in
coastal waters from Japan to the Arabian Sea (Kasuya, 1999). Based on the finding of a
range-wide survey in 2006, most porpoises are concentrated in the middle and lower reaches
from Ezhou to Jiangyin, with the lowest densities in the upper region and the estuaries of the
Yangtze River (Zhao et al., 2008). The current distribution pattern is almost the same as what
Zhang et al. (1993) reported and the porpoises in the upper region from Yichang to Ezhou
(~130 porpoises in 716.4 km) appear to be at the highest risk of local extirpation. The
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