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Migratory fish numbers dropping severely over the last 50 years

Like many migratory fish, chinook salmon are threatened by overfishing, habitat degradation, and dams that block their migration from the sea to upriver spawning grounds. Photo:National Geographic

 

Migratory fish numbers dropping severely over the last 50 years

 

By Patryk Krych | The World Daily | JULY 28th 2020

 

Since 1970, it’s been found that the total number of migratory fish have been steadily dropping, and have thus far plummeted by an entire 75%, according to a study. A “catastrophic” amount, the researchers say.

This study, called the Living Planet Index for Migratory Freshwater Fish, is considered to be the first in the world that focuses on a full and comprehensive study on the status and wellbeing of migrating fish populations.

The statistics were found to be far more disastrous in Europe, where the populations of sturgeons and eels were both noted to have been down by an entire 90%. The causes were narrowed down to be a mixture of the climate crisis, overfishing, increased water pollution and an overall increase in the building of dams, globally.

“The statistics are shocking but we know migratory fish populations can bounce back. We need to act now before populations get to the point where they are too low to recover. Now is the time to value migratory fish and the rivers that sustain them,” said Herman Wanningen, Founder of the World Fish Migration Foundation (WFMF).

Certain species of fish are considered vital for the preservation of particular ecosystems. Salmon, trout and giant catfish are all important in this way by carrying nutrients from the oceans upstream with them. These are nutrients considered important for other land species, such as bears and wolves, or birds that prey on the fish.

The migratory fish also serve as a vital source of food for millions of people around the world, particularly impoverished people and hunters.

The scientists heading the study went on to comment that the situation, while bleak, may in fact be all the bleaker than we expect, seeing as they calculate that the declines had begun even before 1970. Historically, in the Great Lakes in North America, the populations of sturgeon have overall dropped by around 95%. There is also further investigation to be done in rivers such as the Amazon, or in Congo or Mekong, where scientists fear the declines may be just as great.

The falls since 1970 were far less devastating in North America, where they only dropped by 28%. This is, however, primarily attributed to the great number of dams that were since removed from the country, which are known to be especially harmful to fish populations.

“For migratory fish, there’s nothing worse than a dam,” said an author of the report, Zeb Hogan, at the University of Nevada. He did have some hope, however, that the fish numbers could make something of a comeback: “Almost without exception, where dams have been removed, you see populations bounce back, often much more quickly than anyone anticipated.”

All those who’d collaborated on producing this report have high hopes that it will serve as a revelation to countries to start prioritising freshwater protection strategies, as well as spare more attention for the issue, to find ways to help resolve it. More research as well as trials are expected to be performed.

“Catastrophic losses in migratory fish populations show we cannot continue destroying our rivers,” said Arjan Berkhuysen, affiliated with WFMF. “This has immense consequences for people and nature across the globe. We can and need to act now before these keystone species are lost for good.”

The WFMF also published information about the biggest drivers of population decline, finding that these are typically perpetuated by habitat degradation, change and loss accounting for nearly 50% of threats.

“Not all dams are created equal,” Hogan added. “Some dams are more environmentally damaging than others and how you place, design and operate them is important.” It is vital that when building new dams, recovery plans for fish populations have to be put into some measure of consideration. The more attention is put towards the problem, the better it might be managed in the future.

 

By Patryk Krych | © The World Daily 2020

 

 

Categories:
Environment
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EnvironmentWildlifeWaterEuropeNorth America