Biology Reference
In-Depth Information
The construction of embankments in the dolphin's distribution range within India and
Bangladesh has drastically affected the ecosystem where overflow and flooding are important
cycles in the movements and spawning of flood plain dependent fishes (Smith et al., 1998).
In addition to fragmenting dolphin populations, dams and barrages degrade downstream
habitat and create reservoirs/pondage with high sedimentation and altered assemblages of fish
and invertebrates (IWC, 2000). Luxuriant growth of macrophytes and excessive siltation have
eliminated suitable habitat immediately above Farakka Barrage (Sinha, 2000). A detail
register of water development projects and their effects on the river dolphins in Asia was
published by Smith et al. (2000).
Excess abstraction of the river water for irrigation has lowered water levels throughout
the species' range and has threatened suitable habitat especially in the Ganges where the
mean dry-season water depth has been dramatically reduced in the recent years. The long-
term implications of the reduction of dry-season flows in the Ganges are catastrophic for the
survival of
susus
.
Dredging and development of the river environment has altered its nature and eliminated
counter currents, one of the most preferred habitats of the dolphin and where the dolphins
spend much of their time. Heavy river traffic is drastically increasing in the Ganges and
Brahmaputra. This may result in habitat restriction, noise pollution, depletion of prey base
and changes in feeding behavior of the susu in the rivers.
Other sources of habitat degradation include dredging (Smith et al., 1998) and the
removal of stones, sand (Mohan et al., 1997) and woody debris (Smith, 1993). These
activities threaten the ecological integrity of the river environments, especially in small
tributaries where suitable habitat is more confined and therefore more vulnerable to local
sources of degradation.
Pollution
Pollution by fertilizers, pesticides, and industrial and domestic effluents is dramatic in the
Ganges River; about 1.5 million metric tons of chemical fertilizers and about 21,000 tons of
technical grade pesticides were dumped annually to the Ganges-Brahamaputra river system in
India during 2002-2003 (Source: www.ncipm.org.in/asps/pesticides.asp). Senthilkumar et al.
(1999) determined concentrations of polychlorinated biphenyls (PCBs),
hexachlorocyclohexane (HCH), chlordane compounds, and hexachlorobenzene (HCB) in the
Ganges River dolphin blubber, muscle, kidney, liver and prey collected from stomach of the
dolphins collected during 1993 through 1996 from the River Ganges in and around Patna,
India. Comparison of organochlorine concentrations with values reported for samples
analyzed during 1988 through 1992 suggested that the contamination by these compounds has
increased in the river. Kannan et al. (1997) determined concentrations of butyltin compounds
in dolphins, fish, invertebrates and sediments collected from the Ganges in and around Patna.
Total level in dolphin tissues was up to 2000 ng g
-1
wet wt, which was about 5-10 times
higher than in their diet. The biomagnification factor for butyltins in river dolphin from its
food was in the range of 0.2-7.5. Butyltin concentrations in Ganges River organisms were
higher than those reported for several persistent organochlorine compounds.
Recently perfluorinated compounds (PFCs) were analyzed in the biological samples
including the Ganges dolphins (n = 15) from the Ganges at Patna. The arithmetic mean PFOS
(perfluorooctanesulfonate) concentration found in the liver of the Ganges River dolphin was
27.9 ng g
-1
ww. Biomagnification factors (BMF) of PFcs were estimated for the Ganges River
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