Efforts to protect rapidly declining freshwater fish populations may not be enough.
Just a few hundred years ago, the world's rivers and lakes teemed with gigantic fish. Freshwater fish were so plentiful that they were used to feed farm animals and fishermen found it hard not to make a catch, according to a new review of historical accounts.
Oceans get most of the attention when it comes to aquatic conservation. But the new study suggests that freshwater species have declined precipitously, too, and that conservation efforts aren't aiming big enough when it comes to rivers, lakes and streams.
"When you look at these accounts, it is pretty amazing how abundant and especially how large these fish species were that people wrote about," said Kirk Winemiller, a fisheries ecologist at Texas A&M University in College Station, Texas. "We have a very inaccurate view of that history."
Along with colleague Paul Humphries in Australia, Winemiller looked back through newspaper articles, diaries and other historical records dating back to the arrival of European settlers in the mid-1800s in Australia and the early-1600s in North America.
The researchers didn't crunch numbers or analyze data. Rather, they aimed to get a general picture of what lakes and rivers around the world used to look like.
Bodies of freshwater, they found, have changed dramatically over the years.
In 1620, Captain John Smith wrote that his crew of pilgrims in New England had caught enough sturgeon, salmon, eels and other species in one night to fill 12 hogsheads. These containers measured four feet by 2.5 feet and could hold 1,000 pounds of tobacco each.
In the 1700s, travelers described huge stocks of pike, walleye, catfish and other fish in the Ohio River. In 1804, Meriwether Lewis and William Clark mentioned dense and spectacular salmon runs in the Columbia River in the Pacific Northwest.
In Australia, likewise, explorers caught 200-pound cod and other huge fish on demand, even in the Murray-Darling Basin, where heavy agriculture has decimated many species and big fish are now non-existent. In some places, freshwater fish were so plentiful that they were used as pig feed.
The demise of most of the world's grand freshwater fish, Winemiller said, was a direct result of overfishing. Today, huge lake and river fish live only in the few places in the world that are free of human influence, such as the Guiana Shield in South America.
"People rarely appreciate the major impact that even a fairly moderate amount of fishing has on certain freshwater stocks," said Winemiller, who added that the loss of big predator species reverberates throughout the ecosystem. "The impact started very long ago."
In the last decade or two, scientists have focused mostly on protecting and restoring species in the oceans, where animals were also once much larger and much more numerous than they are today. The new study, with its historical perspective on what's possible in bodies of freshwater, suggests that rivers and lakes may benefit from more aggressive protective measures, like the reserves that are becoming more common in marine areas.
The study also points to freshwater conservation as a global issue, said Zeb Hogan, a conservation biologist at the University of Nevada, Reno, even though people often think of rivers and lakes as local resources.
White sturgeons in the Fraser River in British Columbia, for example, are often considered the healthiest population of that fish anywhere in the world. Yet, the river used to hold 10 times as many sturgeons.
"I feel like we're sort of behind the game in terms of global freshwater biodiversity conservation," Hogan said. "Until we start acknowledging that the abundance of large freshwater fish has declined, we're going to continue to set restoration goals too low, and we're going to continue having extinctions."