Yangtze dolphin's decline mirrored by other animals
10 August 2012
By Tom Marshall, Natural Environment Resource Council
Monitoring numbers of the baiji, the now-extinct freshwater dolphin of
the Yangtze river, would also have let researchers track the decline of
other threatened animals, including the Yangtze paddlefish and Reeves'
shad, a new study shows.
Download the study free here:
A disproportionate amount of public attention and conservation resources
tend to go towards big, impressive animals like the baiji, and the paper
ï¿½ published in PLoS ONE ï¿½ suggests that conservationists could take
advantage of this; research on these creatures could be used indirectly
to shed light on the population trends of their less media-friendly
The idea that so-called 'charismatic megafauna' like whales and tigers
could provide an index of the overall health of their environment isn't
new, but it's proved difficult to demonstrate in a rigorous way.
Dr Samuel Turvey of the Institute of Zoology repeatedly travelled to
China over the last few years to interview fishermen on the Yangtze
about when they last saw various threatened species including the baiji.
It's become clear that the baiji is now extinct, but analysing the
results of these interviews shows not only that the paddlefish and shad
have both declined and may also be extinct, but also that the curves
representing their plummeting numbers match that of the baiji very closely.
This was a surprise, as the three animals filled very different
ecological niches and on the face of things might be expected to react
differently to the same threats and environmental pressures.
'There was no reason to think that these species would have similar
patterns of decline over time - they're very different in their ecology
and in how they were exploited, although we know that all three were
affected by fisheries,' Turvey says. 'There's very little information on
the shad and the paddlefish, so we can only infer the pattern of their
declines retrospectively - we've only found out what happened to them
when it's already too late. Conservation resources are limited and are
likely to be focused on charismatic animals, but because the status of
such animals can match that of other species, we can at least try to get
as much benefit as possible from that.'
One common thread is that all three species used to migrate up and down
the river to get to better feeding or breeding grounds, so their
reproductive cycles were more easily disrupted by barriers like dams
that blocked their passage. They also all suffered badly from
overfishing, as well as pollution and other environmental problems.
Other non-migratory animals, such as members of the carp and catfish
families, are still relatively common in the Yangtze despite its
On the other hand, changes in the frequency of sightings of the finless
porpoise, another large aquatic mammal that still survives in the
Yangtze, weren't linked to those of the other animals.
Turvey isn't sure why. The porpoise isn't migratory, so it doesn't share
the feature that could have contributed to the other three species'
increased vulnerability. He suggests that because porpoises are still
encountered by fishermen fairly regularly, it's harder to document
changes to the state of their population using last-sighting reports.
The porpoise is also highly threatened and is declining too, but Turvey
is hopeful that efforts to protect it will be more effective than they
were for the baiji. Because the river ecosystem has been damaged so
badly, the best hope for protecting animals is to set up reserves away
from the main river, where animals can be protected and won't face the
same fierce environmental pressures. Efforts to do this for the baiji
never got off the ground, whereas porpoise reserves are already in place
and working well.
He adds that the research could be applied in other river ecosystems
with big, media-friendly inhabitants, such as Ganges or Irawaddy dolphins.
Turvey, S.T., Risley, C.L., Barrett, L.A., Hao, Y. & Wang, D. (2012).
River dolphins can act as population trend indicators in degraded
freshwater systems. PLoS ONE 7(5): e37902.
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