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gillnets. Other studies indicate that bycatch in gillnets is adversely impacting marine
populations of finless porpoises (Jefferson & Curry, 1994; Zhou et al., 1995; Reeves et al.,
1997; Yang et al., 1999). Because the preferred habitat of the Yangtze finless porpoise
overlaps extensively with gillnetting areas in the river (Yu et al., 2005), the impact of gillnet
mortality may be much more serious than has been generally assumed based on the
infrequency of actual reports.
Boat traffic, which is increasing rapidly in the Yangtze River and lakes, also likely causes
mortality of cetaceans (from propeller strikes) and boat noise may mask their social
communication and ability to forage efficiently (Wang et al., 1998, 2000; Wang et al., 2006).
Widespread mining of the river bed, lake beds and banks (much of it is illegal) has been
destroying important habitat of the porpoise's prey and adversely affecting primary
productivity. This problem is especially serious in Poyang Lake, currently with a population
of around 400 finless porpoises (Xiao & Zhang, 2000; Wang et al., 2006; Zhao et al., 2008).
Compared with cetaceans that live in marine habitats, riverine forms may be at a higher risk
from pollution. Indeed, cetaceans in rivers generally occur in the world's most densely
populated human environments (Reeves et al., 2000a). Four hundred million people live in
the Yangtze River basin and thousands of factories along the river bank discharge tremendous
quantities of domestic sewage and industrial effluents. Furthermore, because rivers are
relatively small water bodies, their water quality can be degraded much more easily than
larger water bodies, such as the oceans are. However, relatively few data exists which
assesses the impacts of pollutants on Yangtze finless porpoise health, fertility or population
status. In April 2004, five porpoises died in Dongting Lake within one week, apparently due
to the combination of a short-term exposure to the pesticide
hostathion
and a long-term
exposure to mercury and
chromium
(D. Wang, unpublished data). Finally, water development
projects, especially dams, have major effects on river ecology. In the Yangtze River system,
structures can block porpoise movements between the river and adjoining lakes or tributaries
(Liu et al., 2000; Smith & Reeves, 2000), as well as the movements of their prey (Xie &
Chen, 1996). The Three Gorges Dam in particular has altered and will continue to alter
downstream hydrologic conditions in the Yangtze River (Tong et al., 2008), and
consequently, may adversely affect the habitat of the baiji and finless porpoises, in the river.
Although the relative importance of each of the above threats has not been quantified, all
have contributed to the decline of the Yangtze finless porpoise. And despite the fact that for
many years these same factors were also known to be pushing the baiji towards likely
extinction, none has been aggressively or seriously addressed and most of them have
escalated dramatically over recent decades. Consequently, we must reiterate that immediate
action is urgently needed to reduce the threats, with highest priority given to areas with
greatest abundance in all regions (see above).
P
ROGRESS OF
C
ONSERVATION
On the first Workshop on Biology and Conservation of the Platanistoid Dolphins held at
the Institute of Hydrobiology of CAS, Wuhan on October, 1986, Chen & Hua (1989)
proposed three measures for protecting baiji: 1. in situ conservation by establishing natural
refuges in the river; 2. ex situ conservation by establishing semi-natural reserves in some
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