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Fish species that make enormous migrations through inland waterways are confronting a combined risk from human-made barriers, contaminants, and excessive harvesting hindering them from accessing their breeding sites.

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

"These aquatic species sustain countless numbers of communities worldwide, so for people, they're very important," said a co-author researcher on the report.

A team of global experts examined more than 15,000 types of migrating freshwater species – which make up half of all known fish – and determined their populations had declined by an staggering 81% in the last half century.

The authors stated that for an extended period, this group of species has been ignored but "constitute an vital part of community survival."

Excessive Harvesting and Environmental Degradation

The priority group is made up of fish that are both threatened and also valued culturally for worldwide societies.

"For example, the tiger of the river is an symbolic fish of the Himalayan region. Numerous individuals in that area cherish that fish for cultural and spiritual practices that extend well past monetary worth," explained a conservation specialist who worked on the study.

Like many fish on the list, it is confronting two primary pressures: overfishing and loss of home.

"Habitat loss encompasses things like obstructions that divide a waterway, and can alter the seasonal patterns of a river, which results in fish not being able to connect to their spawning grounds," the spokesperson added.

Disruption to migratory routes is an challenge that is particularly prevalent in Europe, where fish come across a barrier to their routes every kilometre.

Frequently the obstructions are unnoticed structures that are no longer needed and could be eliminated, said an conservation charity lead.

But the combined impact on migratory fish is massive: "It can have a profound effect in terms of the energy reserves fish are consuming to pass the [barriers]."

That renders them more vulnerable to disease. They're more inclined to get hunted. They will reproduce in less-than-ideal grounds."

Conservation Success

The majority of species will traverse national boundaries on their mammoth migrations. This demands coordinated efforts between states to address these issues and guarantee the restoration of local populations, explained a study contributor.

The international conservation agreement is a international UN convention created in 1979 which requires nations to collaborate to conserve migrating species of all kind.

The United Nations is now recommending that the thirty priority species be listed to the treaty at its yearly meeting in the near future.

The Saiga antelope is an case study of a species that has benefited from being protected under the treaty.

Following a catastrophic decline, an international conservation initiative was established and since then population levels have increased dramatically.

"Conservation efforts has traditionally been on some of the more charismatic species, such as big cats," commented a senior UN representative.

The official noted it was now the turn of migratory freshwater fish to receive international efforts.