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Fish species that make enormous journeys through rivers, lakes, and ponds are confronting a multifaceted threat from dams, pollution, and overfishing hindering them from accessing their reproductive sites.

Examples including the Himalayan mahseer and giant devil catfish are among thirty key species which have now been selected for global conservation by the UN in a latest report.

"Freshwater fish sustain hundreds of millions of individuals around the world, so for societies, they're crucially significant," stated a lead scientist on the assessment.

A panel of global experts examined over 15,000 species of freshwater migratory fish – which represent 50% of all fish species – and discovered their numbers had declined by an estimated 81% in the last half century.

The researchers argued that for an extended period, this class of species has been ignored but "constitute an vital part of community survival."

Excessive Harvesting and Environmental Degradation

The shorter list is comprises fish that are both threatened and also valued culturally for global societies.

"For example, the tiger of the river is an revered fish of the Himalayas. A great many individuals in that region value that fish for cultural and spiritual practices that extend well past financial values," noted a freshwater expert who contributed to the report.

Similar to other fish on the list, it is experiencing two primary pressures: excessive fishing and environmental destruction.

"Environmental degradation encompasses things like obstructions that divide a river system, and can change the natural flow regime of a river, which leads to fish not being able to connect to their breeding grounds," the expert said.

Obstruction to migration is an issue that is notably prevalent in some continents, where fish encounter a barrier to their paths on average every 0.6 miles.

Often the obstructions are unnoticed structures that are redundant and could be eliminated, said an environmental charity lead.

But the cumulative impact on migrating fish is enormous: "It can have a profound effect in terms of the strength fish are using to pass the [barriers]."

That leaves them more prone to disease. They're more likely to get eaten. They will breed in poor areas."

Back from the Brink

Most fish will cross national boundaries on their extensive migrations. This demands collaborative work between nations to tackle these issues and secure the restoration of national stocks, argued a study lead author.

The international conservation agreement is a worldwide United Nations treaty established in 1979 which obligates countries to work together to safeguard migrating species of all kind.

The UN is now proposing that the 30 fish species be listed to the agreement at its annual conference in the coming years.

The Saiga antelope is an example of a species that has benefited from being protected under the convention.

Following a catastrophic decline, an international anti-poaching effort was established and since then numbers have recovered significantly.

"The focus has clearly been on some of the more charismatic species, such as big cats," commented a senior conservation official.

She said it was now the turn of river fish to benefit from similar efforts.