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Aquatic species that embark on massive journeys through inland waterways are facing a multifaceted risk from human-made barriers, contaminants, and excessive harvesting stopping them from reaching their reproductive areas.

Examples including the Himalayan mahseer and giant devil catfish are among 30 flagship species which have now been selected for global conservation by the UN in a new assessment.

"Freshwater fish provide for hundreds of millions of people globally, so for people, they're incredibly vital," stated a co-author researcher on the assessment.

A team of international researchers assessed over 15,000 types of freshwater migratory fish – which represent 50% of all fish species – and discovered their abundance had fallen by an estimated 81% in the past 50 years.

The scientists said that for an extended period, this class of species has been ignored but "constitute an vital part of people's survival."

Excessive Harvesting and Environmental Degradation

The focused list is consists of fish that are both threatened and also culturally significant for global communities.

"As an instance, the golden mahseer is an iconic fish of the Himalayan region. Numerous people in that area cherish that fish for traditional and sacred practices that extend well past monetary worth," commented a freshwater advocate who worked on the report.

Like many fish on the roster, it is confronting two key threats: excessive fishing and loss of home.

"Environmental degradation encompasses things like dams that fragment a waterway, and can alter the normal water flow of a river, which causes fish not being able to connect to their breeding areas," the expert added.

Obstruction to migratory routes is an challenge that is especially widespread in Europe, where fish encounter a barrier to their routes on average every 0.6 miles.

Frequently the barriers are small structures that are redundant and could be taken out, said an environmental charity lead.

But the cumulative effect on migratory fish is massive: "It can have a significant effect in terms of the energy reserves fish are expending to navigate the [barriers]."

That leaves them more susceptible to disease. They're more prone to get hunted. They will reproduce in poor areas."

Conservation Success

Most fish will pass over national borders on their mammoth journeys. This necessitates joint actions between states to combat these threats and secure the recovery of local populations, said a report lead author.

The global treaty on migratory species is a worldwide United Nations agreement established in 1979 which obligates nations to work together to protect migratory species of many kinds.

The UN is now recommending that the 30 fish species be listed to the agreement at its yearly meeting in the near future.

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

Following a catastrophic decline, an global conservation team was created and since then abundance have rebounded substantially.

"Conservation efforts has often been on some of the more charismatic species, such as large mammals," stated a high-ranking UN official.

She added it was now the turn of these aquatic migrants to receive coordinated protection.