Standing on the shores of Thailand's Lake Monster, angler Brendan O'Sullivan knew there were endangered giants lurking near his baited hook—and that conservationists were happy to have him score a rare catch.
The 7-acre (2.8-hectare) lake is one of several created in recent years near Bangkok for anglers who want to hook some of the world's most exotic fish.
Lake Monster alone boasts roughly two dozen types of freshwater fish, many of them threatened with extinction.
While this might seem like a conservationist's nightmare, some praise the operation as an example of a burgeoning partnership between anglers and biologists who hope that catch-and-release sportfishing could help save at-risk animals.
"This is allowing anglers to catch rare species without having to go into the wild and try to remove a very rare fish from its natural habitat," said Zeb Hogan, a fisheries biologist at the University of Reno in Nevada.
As head of the National Geographic Society's Megafishes Project, Hogan is leading efforts to find, study, and preserve the world's largest freshwater fish, some of which are highly endangered but poorly understood, compared to ocean going behemoths. (National Geographic News is part of the National Geographic Society.)
Part of the project is to analyze catch records to learn more about population trends. The data provide valuable information on the animals' abundance, size, and movements, Hogan said.
"It's become more common for me to team up with recreational fishers who share the same goal. That is, to catch these fish but also to release them," he added. "What we should do is minimize the harm to the fish and maximize the information we're gaining in order to protect them."
In some cases, artificial lakes and breeding centers can be the only places where experts can study rare species in the flesh.
At I.T. Lake Monster—the lake's official name—Hogan recently had the chance to examine a dog-eating catfish caught by anglers. The massive predator—named for stories of fishers luring it with dog meat—has almost disappeared from Southeast Asia's Mekong River.
"I've never seen one in the wild," Hogan said, "so this is pretty exciting for me."
For now, however, one of the chief concerns among conservationists like Hogan is the well-being of fish living in sport lakes.
Caught by hook over and over again, the fish can, in extreme cases, sustain irreparable damage to their mouths or gills.
"I always feel a little uneasy about working with recreational fishers, who, some say, are hurting fish for fun," Hogan said.
On the other hand, he noted, it's in everyone's interest to ensure that these fish don't die out.
"And there are quite a few positive impacts of recreational fishing," he said. "Not only do the anglers release the fish they catch, they also bring in money to local economies that need it."
Lake Full of Giants
Many fish from other tropical countries thrive in Thai lakes, and in recent years the country has become a breeding center for exotic species.
Lake Monster's owner, Ittiporn Parnitpechedpong, says he began stocking it two years ago so his friends could fish for fun. But what started as a hobby has grown into an increasingly lucrative business.
"People want to come and fish for these big fish, especially because many of these exotic species are new for Asia," Parnitpechedpong said.
Lake Monster is now a haven for the Mekong giant catfish, a Southeast Asian beast that has seen its wild population drop by about 95 percent over the past century.
At 9 feet (2.7 meters) long and 646 pounds (293 kilograms), a Mekong giant catfish currently holds the record for the largest freshwater fish ever caught (see photos).
Lake Monster also hosts alligator gar, which can grow as long as 10 feet (3 meters) and weigh 300 pounds (135 kilograms).
These North American giants are not listed as endangered, but habitat loss and overfishing have taken a toll on the species' preferred spawning habitats, contributing to significant population declines.
Conservationists are also concerned about another giant inhabitant of Lake Monster, the arapaima, which is becoming increasingly rare in its native Amazonian habitat.
Arapaima can grow more than 10 feet (3 meters) long and 400 pounds (180 kilograms). As an air breather, the species is vulnerable to hunters with harpoons when it surfaces for air every 10 to 20 minutes.
Care and Respect
A recent four-hour visit to Lake Monster yielded about 20 catches for angler O'Sullivan and a friend.
"You can talk about the purists who want to go and fish on the [native] waters, but the Amazon is a mighty big river, and the chance of catching anything there is minimal," O'Sullivan said. "Here you're ensured of a good day."
Rick Humphreys, who co-owns a Thai sportfishing outfitter called FishSiam, added that while he and other anglers enjoy the sport, they are also committed to conservation.
"I have no wish to kill any [endangered] fish," Humphreys said. "Every time I catch a fish, I try to treat it with the utmost care and respect."
Fisheries biologist Hogan said he sees opportunities for conservationists and anglers to work together in wild settings, too.
In April, Humphreys and his FishSiam team called on Hogan to join them on Thailand's Bang Pakong River to examine giant freshwater stingrays. The anglers had caught several of the rare rays, included a pregnant female, which gave birth while being held by the fishers.
According to Humphreys, the event was a sign of the partnership emerging between conservationists and anglers.
"We can help each other learn more about understudied creatures."