People think of elephants, tigers and sharks as a bellwether for how the environment is doing, but monster fish, two dozen species of large freshwater fish weighing more than 200 pounds, are an alarming indicator of the health of aquatic ecosystems around the world.
"These big fish are in a steep decline," Zeb Hogan, conservation biologist and researcher in the Department of Biology, said. "The disappearance of aquatic animals is a freshwater extinction crisis."
These fish have been silently disappearing at dozens of locations around the world. Approximately 70 percent of monster fish species are considered threatened. In North America, nearly 40 percent of freshwater fish are threatened and 61 species are presumed extinct.
Hogan, a National Geographic Fellow and a Scientific Councilor for Fish for the United Nations Convention on Migratory Species, has been investigating these megafish for more than a decade, traveling to remote regions of the world to find, study and protect them. The National Geographic Society has supported Hogan's work since 2002, including the Monster Fish project for the past 10 years. His research is documented in the Nat Geo WILD show "Monster Fish" and in the new featured exhibition, Monster Fish: In Search of the Last River Giants, at the National Geographic Museum in Washington, D.C., from March 26 to Oct. 14, 2015.
"Giant freshwater fish are every bit as important to the health of their ecosystems as the top predators of land and sea. These freshwater species deserve the same attention we give to tigers and whales," he said.
While he sees firsthand the decline of the big fish, Hogan is also encouraged by conservation efforts he has helped communities put in place, such as on the Mekong River in Thailand where he captured and released his first large freshwater catfish, a 645-pound fish, in 2005. The river is known for its big stingrays and catfish.
"These are all incredibly rare animals that most people would never have a chance to see or appreciate," Hogan said. "This exhibit is a window into an underwater world that few of us have ever experienced. They can grow to over 20 feet in length, some living over 100 years, and many are on the edge of extinction. The exhibition is the culmination of years of work by many people to better understand and protect them."
As a Scientific Councilor for Fish, Hogan is part of a working group of scientists and interested parties from around the world who provide scientific guidance on decisions to list species as endangered. In November, at the United Nations Convention on Migratory Species Conference of Parties in Brazil, 20 new species of fish were added to the endangered list, including one freshwater megafish, the sawfish.
Determining which species are on the brink of extinction is the primary goal of Hogan's research. Hogan said dams, pollution, habitat degradation, invasive species and overfishing are the biggest threats. In the majority of cases, fish are subject to more than one stressor.
Hogan, who has a doctorate in ecology, has worked with nearly 100 scientists on the Monster Fish project, which spans six continents (North America, South America, Africa, Europe, Asia, and Australia) and encompasses several of Earth's most diverse freshwater ecosystems - ecological treasures - including World Heritage Sites, Ramsar Wetlands of International Importance and United Nations Environment Program Biodiversity Hotspots.
Other sites include the Amazon River, Mekong River, Mississippi River, Nile, Lake Baikal watershed in Russia, Murray-Darling River in Australia, tributaries of the Danube and Yangtze River in China.
Hogan travels to the most endangered of these environments, striving to save critically endangered fish and the livelihood of people who share their habitats.
The Monster Fish exhibition, for which the University of Nevada, Reno is the Educational Partner, takes visitors on a journey to several river basins worldwide to learn about the awe-inspiring fish and the cultures and places that depend on them. The exhibition profiles the extraordinary biology and behaviors of giant freshwater fish. It also offers the opportunity to investigate how scientists learn about these fish and develop solutions to save them.