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observed density in this region decreased from 0.11 porpoises/km in 1991 (Zhang et al.,
1993) to 0.02 porpoises/km in 2006 (Zhao et al., 2008). Moreover, there appeared to be
significant gaps in the distribution in this part of the river, since no porpoises were detected
during either the upstream or the downstream passes by the two survey-boats in the 150 km
subsection between Yueyang and Shishou in 2006 (Zhao et al., 2008). Despite the possibility
of false negatives in determining the presence of finless porpoises in that study, the number of
porpoises in this region must be extremely low or nil. The ~90 km subsection upstream of this
gap included the most-upriver population (roughly 60 porpoises, Zhao et al., 2008). If the
porpoises in this subsection were to become extirpated, the linear extent of the recent
historical range of this subspecies on the river would shrink by ~400 km, or by about 24% of
the whole range in the main stem of the river (Zhao et al., 2008). It may be noteworthy that
this was also the river section where the baiji were first eliminated (Zhou et al., 1977; Chen,
et al., 1997; Zhang et al., 2003). Although limited photo-identification studies suggested that
baiji traveled over hundreds of kilometers up and down the river (Zhou et al., 1998a), the
significantly different patterns of mtDNA haplotypes among finless porpoises in different
sections of the Yangtze River implies that these animals do not move far (Zheng et al., 2005).
This means that even if all threats were eliminated and habitat conditions improved, there is
little chance that porpoises from other areas would repopulate the upper region of the Yangtze
River below Yichang and above Yueyang. Therefore, unless the current trend is reversed,
there seems to be a good chance that finless porpoises will soon disappear permanently from
that area. In the middle and lower regions between Wuhan and Jiangyin, the porpoise
distribution appeared continuous but their abundance decreased from the (presumably
underestimated) level of 1,652 (surveys of 1984 to 1991, Zhang et al., 1993) or 1,481
(surveys of 1989 to 1992, Zhou et al., 1998b) to the current level of ~800 (Zhao et al., 2008).
T
HREATS AND
C
ONSERVATION
A number of anthropogenic factors are known or suspected to be responsible for the
population decline and range contraction of the Yangtze cetaceans. For example, Chen et al.
(1997) reported that among 64 baiji specimens collected (33 were collected from 1973 to
1983 in middle reaches from Yichang to Hukou, and 31 were collected from 1978 to 1985 in
lower reaches from Hukou to Shanghai) (Figure 1), 53 were the result of different kinds of
human activities, use of harmful fishing gears, boat collisions, and explosives used to widen
and deepen the shipping channel. Since baiji and the Yangtze finless porpoise share the same
river and almost the same habitat, the porpoise must have been facing the same kind of threats
as that of the baiji.
Turvey et al. (2007) concluded that entanglement in gear used in unregulated and
unselective fishing (rolling hooks, electrofishing gear and gillnets) was the main factor
responsible for the probable extinction of the baiji. This same factor likely explains much of
the ongoing decline of the Yangtze finless porpoise (Wang et al., 1998, 2000, 2005; Wang et
al., 2006). Illegal fishing is widespread in the Yangtze River (Reeves et al., 2000b; IWC,
2001; Smith et al., 2007) and was observed daily during a rang-wide survey in 2006 (Turvey
et al., 2007). Zhou & Wang (1994) reported that ‗most' of the 80 finless porpoise specimens
collected by Nanjing Normal University since 1974 had been killed by rolling hooks or
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