The Quest to Save Freshwater Leviathans

WWF scientists are trying to determine why the world's largest freshwater fish are disappearing. photo: Zeb Hogan

World Wildlife Fund and National Geographic have launched a groundbreaking scientific adventure to find the world's largest freshwater fish. Led by WWF science fellow Dr. Zeb Hogan, the search began on the Mekong River in Southeast Asia, and will explore rivers and lakes around the world for fish such as the Mekong giant catfish, which at 10 feet long and weighing more than 600 pounds is listed by The Guinness Book of World Records as the Earth's largest freshwater fish. Scientists believe that even larger species exist.

Such natural marvels seem like they wouldn't be too hard to spot, but despite their size, finding and studying these freshwater giants will not be easy. They are extremely rare and getting rarer due to threats like overfishing and habitat destruction, including the construction of dams that block migrations and isolate some populations. Some of these fish are already listed on IUCN's Red List of Threatened Species and, with the information gained form this study more species will likely be listed for the first time.

"These are absolutely amazing animals. They are unique and beautiful but disappearing fast," said Hogan. "This study has the potential to set new records. We're looking to find the largest freshwater fish in the world, identify where they live and figure out why they are disappearing." Hogan believes that the disappearance of these giant fish could be the first warning sign of the trouble ahead for freshwater ecosystems.

Many of the world's freshwater wonders are being threatened by overfishing. photo: Zeb Hogan

Scientists will be searching for goliath catfish, giant stingrays, razor-toothed gars, massive carps, caviar-producing sturgeon, and predatory salmon, all of which can grow to six feet or longer and weigh more than 200 pounds. The study is being funded by WWF's Conservation Science Program and the National Geographic Society's Emerging Explorers Program.

"These giants are the freshwater equivalents of elephants and rhinos, and if they were visible to us on land the world wouldn't stand by while they disappeared," said Robin Abell, freshwater conservation biologist with World Wildlife Fund. "This study will give us new insight into how these species live and what threatens their survival. In the end, we'll know better how to manage fishing and protect habitats to save the species for the future."

A century ago, Mekong giant catfish, for instance, were found the entire length of the river from Vietnam to southern China. Since then populations of this species, and other giants in the same system, have plummeted. Scientists estimate that the total number of Mekong giant catfish has decreased about 90 percent in just the past two decades.

"By examining this diverse group, we hope to understand why many species are declining nearly everywhere," continued Hogan. "Our goal is to draw those connections in the hopes that we can better protect them."

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