FRESHWATER MEGA-FAUNA
SOME
HAVE SURVIVED for hundreds of millions of years, but many of the world’s
freshwater Mega-fauna—including sumo-sized stingrays, colossal catfish, giant
turtles, and gargantuan salamanders—may soon find themselves on the brink of
extinction.
For the first time, researchers have quantified the
global decline of freshwater mega-fauna—including fish, reptiles, amphibians,
and mammals—and the results paint a grim picture. In four decades since 1970,
the global populations of these freshwater giants have declined by almost 90
percent—twice as much as the loss of vertebrate populations on land or in the
oceans.
Large fish species, such as sturgeons, salmons, and
giant catfishes, are particularly threatened, with a 94 percent population decline. Most large freshwater reptile and
many mammal species are also in trouble. The baiji, a Chinese river dolphin, is likely the first dolphin species
driven to extinction by humans, and the Chinese paddlefish, which can grow 20
feet long, has not been seen in over a decade. Other species may be down to
their last few individuals.
UNDERWATER
SPECIES
Freshwater ecosystems are generally less studied than
their marine counterparts, despite being home to a third of all vertebrate
species and nearly half of all fish species worldwide. While population
declines have been well-documented for both terrestrial and marine mega-fauna.
For the study, a team of international researchers
compiled population data on 126 out of 207 freshwater species weighing at least
30 kilograms (66 pounds) from 1970 to 2012, drawing in part on The Living Planet Index, a database managed
by the Zoological Society of London in cooperation with the World Wildlife
Fund. While that index shows that populations of all freshwater species
declined by 83 percent during roughly the same period, the new study shows an
even higher rate of decline in big freshwater animals, at 88 percent.
Public awareness of the freshwater biodiversity
crisis is limited, with many people unaware that the giant creatures even
exist. “They are not like tigers, pandas, lions, or whales—species that receive
a lot of attention in the media and school education.
Among the biggest threats facing large freshwater
species are overexploitation and
habitat degradation. Many of the
these animals are targeted for meat,
skin, and eggs. Mega-fish in particular tend to be more vulnerable than other fish to dams that block their
migratory routes and limit access to spawning grounds. Large animals also tend
to be slow to mature and have low reproduction rates, making them particularly
vulnerable.
RIVER
MEKONG
The bio-geographic zones that have seen the greatest
declines in freshwater mega-fauna are Indo-Malaya (99 percent) and the
Palearctic, which encompasses Europe, northern Africa, and northern Asia (97
percent). The most critical region may be Southeast
Asia, and in particular the Mekong River, which runs through China, Myanmar, Thailand, Laos, Cambodia
and Vietnam. More than a thousand species of freshwater fish live in
the Mekong, including many of the world’s largest. The Mekong giant catfish,
for example, is the current record-holder for the world’s largest freshwater
fish ever caught, at 646 pounds. Existing
and planned dams on the river may drive the species to extinction and it
could threaten the food security and
livelihoods of millions of people living along the river.
Amid the grim overall findings, the study did
suggest that 13 freshwater mega-fauna species have seen their populations
stabilize or even grow. Among them are the green sturgeon and the American
beaver, both in the United States. In Europe, the Eurasian beaver has returned
to many regions from where it had once disappeared, and in Cambodia, the
population of Irrawaddy river dolphins has increased for the first time in 20
years.
