Stefan Lovgren, University of Nevada Reno – Saving the River Giants

Large marine life doesn’t just live in the world’s oceans.

Stefan Lovgren, research scientist in the college of science at the University of Nevada Reno, looks into protecting the river giants.

Stefan Lovgren is a research scientist in the College of Science at the University of Nevada Reno, as well as the communications director of the USAID research project Wonders of the Mekong. A journalist with more than 25 years of international reporting experience, he is a frequent contributor to National Geographic and the author of several books, most recently “Chasing Giants: In Search of the World’s Largest Freshwater Fish” (University of Nevada Press, 2023).

Saving the River Giants

We know the whale shark is the largest fish in the ocean. But what is the world’s largest freshwater fish? For almost two decades, I’ve followed Zeb Hogan, a fish biologist, on a quest to solve this mystery.  We’ve scoured the world’s waterways for garguantuan gars and colossal carp. But the answer kept eluding us. There were reasons for this. Many giant fish live in remote rivers and are not well studied. They’re also disappearing because of human threats, from overfishing and dam building to pollution and climate change — to the point where they are now among the most critically endanged animals on the planet.

But last year, fishers on the Mekong River in Cambodia caught a 661-pound, 13-foot-long giant freshwater stingray, larger than any freshwater fish ever recorded. Before releasing it back into the river, our research team was able to implant an acoustic tag in the ray that has allowed us to track its movements. This is vital research, because the giant freshwater stingray is a species we previously knew almost nothing about. We’re learning it has a remarkably small home range, and that in turn has helped us identify this stretch of the Mekong as critical habitat for these megafish.

On a global scale, the story of giant freshwater fish is still deeply troubling. One leviathan, the Chinese paddlefish, is believed to have gone extinct during our search. But discoveries like the one in Cambodia show that some populations still remain relatively healthy and saving them is not a lost cause. As global research around these fish ramps up, conservation efforts are increasingly led by local communities eager to protect these animals. As for our search — well, it continues. Who knows what weird and wonderful creatures still lurk out there.