A groundbreaking scientific adventure to find the world's largest freshwater fish starts today on the Mekong River in Southeast Asia. Led by World Wildlife Fund science fellow Dr. Zeb Hogan, the project will explore rivers and lakes around the world for fish such as the Mekong giant catfish, which is listed by The Guinness Book of World Records as the Earth's largest freshwater fish. Some grow to 10 feet in length and more than 600 pounds. Scientists believe that larger species exist. Hogan will work with a network of more than 100 scientists in 17 countries to investigate these fish and find out why their numbers are declining.
"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. These fish are the proverbial canaries in the coal mine for freshwater ecosystems. Their disappearance is often the first warning sign of overfishing or other trouble in the rivers and lakes where they live."
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. Many of these giant fish are threatened by overfishing and habitat destruction. The study is 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."
Despite their size, finding and studying these freshwater giants will not be easy. They are extremely rare and getting rarer. Some are already listed on the World Conservation Union's Red List of Threatened Species and, with the information gained in this study, more species will likely be listed for the first time.
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.
Efforts to save this species from extinction will hinge on many factors - including how well biologists understand the migratory behavior of these animals. So, scientists will tag these elusive creatures and track their movements. In an earlier study, a river catfish Hogan tracked traveled 185 miles in less than a month, more than 3 miles a day.
"This is the first study to examine all of the world's giant freshwater fish," continued Hogan. "Many of these species have hardly been studied at all, and there has never been a study looking at them collectively. By examining this diverse group, we hope to understand why many species are declining nearly everywhere. Our goal is to draw those connections in the hopes that we can better protect them."
The Mekong River Basin is home to more species of massive fish than any river on Earth. It is also the most productive fishery in the world, generating $1.7 billion each year. Fish from the Mekong are the primary source of protein for the 73 million people that live along the river.
Threats to the world's giant fish include dams that block migrations and isolate some populations. Without the ability to move up and down rivers, the fish have fewer opportunities to breed. This cuts down overall numbers and genetic diversity. Navigation projects have also destroyed critical spawning grounds and overfishing has lead to depleted fish stocks and conflict between resource users, highlighting the need for more effective management strategies.