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Fish species that embark on massive migrations through rivers, lakes, and ponds are facing a converging threat from dams, pollution, and overfishing stopping them from arriving at their breeding grounds.

Species like the Himalayan mahseer and goonch catfish are among thirty key species which have now been recommended for worldwide preservation by the United Nations in a latest study.

"Migratory fish provide for many millions of individuals worldwide, so for humans, they're incredibly vital," stated a contributing scientist on the report.

A panel of international scientists evaluated over 15,000 species of migrating freshwater species – which constitute half of all known fish – and found their populations had dropped by an estimated 81% in the previous five decades.

The scientists said that for an extended period, this class of species has been overlooked but "represent an vital part of human survival."

Excessive Harvesting and Environmental Degradation

The priority group is made up of fish that are both threatened and also important for traditions for many communities.

"For example, the tiger of the river is an iconic fish of the Himalayas. A great many people in that area cherish that fish for cultural and spiritual reasons that extend well past financial worth," explained a conservation advocate who contributed to the study.

Similar to other fish on the roster, it is experiencing two key pressures: excessive fishing and habitat loss.

"Environmental degradation encompasses things like barriers that fragment a river system, and can alter the seasonal patterns of a river, which causes fish not being able to access their breeding areas," the scientist said.

Disruption to migration is an issue that is particularly widespread in Europe, where fish come across a blockage to their journeys on average every 0.6 miles.

Often the barriers are small structures that are unnecessary and could be eliminated, said an environmental science lead.

But the cumulative impact on migrating fish is massive: "It can have a profound effect in terms of the energy reserves fish are expending to get over the [barriers]."

That makes them more vulnerable to disease. They're more inclined to get predated. They will breed in suboptimal areas."

Road to Recovery

The majority of species will pass over national boundaries on their lengthy migrations. This requires joint work between governments to combat these threats and ensure the recovery of local populations, said a report co-author.

The global treaty on migratory species is a global United Nations treaty signed in 1979 which requires signatories to cooperate to conserve migratory species of all kind.

The United Nations is now recommending that the thirty fish species be listed to the treaty at its yearly meeting in three years' time.

The distinctive antelope is an case study of a species that has benefited from being included under the convention.

Following a catastrophic decline, an global anti-poaching team was created and since then numbers have recovered substantially.

"Attention has traditionally been on some of the more charismatic species, such as whales," stated a senior conservation representative.

She noted it was now the opportunity of migratory freshwater fish to benefit from similar action.