Why freshwater migratory fish need ‘safe passage’ globally as numbers decline

The dorado mudcat has no supply with long move around years.

The species, a monumental freshwater fish found in the Amazon, migrates from the Amazon estuary in northern Brazil to the foothills of the Andes Mountains in parts of Colombia, Ecuador, Peru, Bolivia and Brazil.

It's a life-long journey for these catfish — one that can take up to 11,000 kilometres. 

But the dorado catfish, and many other migratory freshwater fish like it, are at risk — their journeys increasingly hampered by habitat destruction, overfishing and dams blocking their way

"If you block these migrations … the stocks will disappear and, in some cases, the species will go extinct," Zeb Hogan, a biologist at the University of Nevada, told Day 6 host Brent Bambury.

Hogan led a global assessment on migratory freshwater fish species, published in March by the World Wildlife Fund, the Convention on the Conservation of Migratory Species of Wild Animals and the University of Nevada.

It found that there are 325 species of migratory fish crossing international borders that need deliberate action in order to survive.

"These are species where the populations are either in decline or, in some cases, even at risk of extinction, that need international cooperation for their management and protection," said Hogan. 

As the dorado catfish makes its long trek to the Andes foothills, it must contend with a number of obstacles.

Dams are a big problem, Hogan said, noting they block upstream migration, as well as blocking fish from moving back downstream after they spawn. 

But the dorado catfish also has to deal with habit degradation, such as their spawning ground being turned into a gravel or sand mine, Hogan said, in addition to floodplains being used for agriculture and unsustainable harvest through overfishing.

And these challenges affect more than just Amazonian catfish.

The American eel is one of the other species listed in last month's report, said Steven Cooke, a Canadian fisheries biologist at Carleton University in Ottawa. While the federal government decided against listing the eel as a species at risk, Cooke, who is also the Canada Research Chair in Fish Ecology and Conservation Physiology, said there is cause for concern. 

American eel won't be listed under Species at Risk Act

American eels reproduce in the Sargasso Sea, near Bermuda. The larvae then make their way to the St. Lawrence and up into the Great Lakes. 

Cooke said getting there isn't an issue. It's getting back to those mating grounds near Bermuda that proves challenging. 

"They are long animals," said Cooke. "On their way downstream they encounter hydropower facilities and ... Their length doesn't help them when they're trying to get between turbine blades, [so] we see pretty high levels of mortality."

These fish also provide a lot of value to people and the ecosystems they migrate through, Cooke said. Some cycle nutrients from the ocean into fresh water, which can fuel forest growth, and in some places they're important for food security. 

"We take that for granted here in North America because we can go to the store and buy fish, but there's many places in the world where that's not the case," said Cooke. 

"So these seasonal pulses of migratory fish really help to support low-income peoples and communities," he said. "It was really a safety net for food insecure peoples."

How eel fishing is changing for the Mi'kmaq trying to preserve it

In Canada, some migratory fish, such as the salmon and eel, have important connections to Indigenous communities. 

"They are iconic, too," said Cooke. "The Pacific salmon migration, the Atlantic salmon migrations, some of the sturgeon we have here in Canada, American eel, those are all iconic species that really undertake epic migrations."

There are ways to protect these fish, Cooke said.

"There's some conservation problems where we scratch our heads and we say, 'Hmm, we don't know what to do.' But when it comes to migratory fish, it's pretty simple, and that's to give them safe passage," he said.

But, it's easier said than done. For fish that are crossing international borders, total cooperation among all the countries along the migratory path is needed. 

"It doesn't matter how many jurisdictions do a good job, if there's one place where things are going poorly it's game over, because these animals need to go from A to B to C to complete their life cycle," said Cooke. 

When it comes to the American eel, he said, there is strong joint cooperation between Canada and the U.S., as well as individual states and provinces. But that's not the case everywhere. 

Cooke said some countries lack political will, while others simply don't have the money to make the changes necessary to protect the fish.

Another important part of the survival of these fish is awareness, Hogan said, especially given many of these journeys are unseen under the water. 

"I love sharing the stories of these fish with people," said Hogan, who used to host the TV documentary series, Monster Fish. 

"Part of the solution is to share the stories of these incredible fish, 600-pound catfish, you know, stingray that are 14 feet long in fresh water, and share some of these stories to get people to engage and to care."

Hogan has reason to be optimistic. At a United Nations conference in Brazil focused on the protection of migratory species last month, countries along the Amazon River agreed to take steps to protect the dorado catfish. 

"We have a road map for action, we have countries that have come together to take action to help these fish," said Hogan. 

"I hope that five to 10 years from now we will be in a much better place than we are now."

Interview with Zeb Hogan produced by Pedro Sanchez

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