44 | New Scientist | 3 October 2020
to see off the Chinese paddlefish, and
has reduced megafish populations in the
Mekong – the most heavily fished river
system in the world – to “close to zero”, says
Jähnig. In this part of Asia, species in the
firing line include the Mekong giant catfish
(Pangasianodon gigas), giant Siamese carp
(Catlocarpio siamensis) and shark catfish
(Pangasius sanitwongsei).
Overfishing has also been the scourge
of sturgeons (see “Caviar catastrophe”, left).
But despite this generally gloomy picture,
there are glimmers of hope. The near-certain
extinct status of the Chinese paddlefish,
on top of the earlier loss of the river dolphin
there and the generally rotten state of the
Yangtze, seems to have focused the minds
of the Chinese government, says Jarić,
who works closely with freshwater biologists
in the country.
“The paddlefish was a wake-up call
in China,” says Jarić. After this, he says,
there was a meeting between researchers
working on fish in the Yangtze, the
International Union for Conservation of
Nature, conservation group WWF and the
government to develop some new actions.According to another recent assessment,
even though rivers and lakes (excluding
wetlands) cover just 1 per cent of Earth’s
surface, they harbour around a third of
all vertebrates and half of fish species.
Freshwater vertebrates are declining faster
than their terrestrial and marine cousins.
Despite this, freshwater ecosystems are
neglected in conservation policy. They really
ought to be seen as a separate – and uniquely
vulnerable – category alongside terrestrial
and marine ecosystems, but are usually
just lumped in with the former. “If you
look at how freshwaters are represented
in conservation frameworks, they lack
their own goals,” says Jähnig. Freshwater
biologists were planning to lobby the
2020 UN biodiversity conference in China
for better recognition, but the meeting
has been postponed until at least 2021
because of the covid-19 pandemic.
The animals bearing the brunt of this
neglect are the 80 or so species of really
big fish – not just sturgeons, but also giant
catfish and carp, electric eels, lungfish,
freshwater rays, river sharks and more.
Since 1970, their populations have declined
by 94 per cent on average. Most of them are
endangered; some are probably doomed.Vital yet vulnerable
These aren’t just aesthetic losses. Ecologists
regard megafauna as disproportionately
important for biosphere functioning.
Large animals, for example, eat and excrete
a lot and so are vital for the nutrient cycling
that other, smaller species rely on.
Big fish are especially vulnerable for
a number of reasons, says Jähnig. “They
reproduce really late [in life] so they need
to have the right conditions for a long time;
some need 10 or 15 years to mature. They
have relatively few offspring, and they
require a big habitat. Many are migratory,
so they wander up and down stream and
that means if there is a barrier like a dam,
they get into trouble.”
“There are multiple threats,” agrees Jarić.
“Damming, pollution and big pressure
from the human population.” That includes
being hunted for food. Overfishing helpedSturgeon – long-lived fish
with a shark-like fin on their
back — used to be common
across Eurasia and North
America, but demand for their
roe in the form of caviar has
reduced them to a few
diminished and often
unsustainable populations.
Between 1985 and 2005, the
sturgeon population in the
Caspian Sea – the source of
90 per cent of the world’s wild
caviar – collapsed. Even today,
sturgeon poaching is big
business, even though there
are hardly any fish left.
“Poachers face high
punishments, but the money
they can earn is a big
motivation,” says Ivan Jarić at
the Czech Academy of Sciences
Institute of Hydrobiology. “They
can get rich from a single catch.”
One beluga sturgeon can supply
60 kilograms of caviar worth
€30,000 to the poacher. And
as sturgeon species get rarer,
the price spirals ever upwards.
These fish are now farmed for
caviar, but connoisseurs say it
is an inferior product. “Illegal
fishing is very profitable and
hard to control,” says Jarić.Caviar
catastrophe
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