Fish species that make enormous migrations through inland waterways are grappling with a combined danger from human-made barriers, contaminants, and excessive harvesting preventing them from accessing their reproductive grounds.
Examples including the Himalayan mahseer and giant devil catfish are among thirty flagship species which have now been prioritised for global conservation by the UN in a recent report.
"Freshwater fish support countless numbers of individuals around the world, so for societies, they're incredibly vital," stated a co-author researcher on the study.
A panel of international researchers evaluated over 15,000 types of freshwater migratory fish – which constitute 50% of all known fish – and determined their abundance had declined by an staggering 81% in the last half century.
The scientists said that for an extended period, this category of species has been ignored but "represent an vital part of human survival."
Excessive Harvesting and Environmental Degradation
The focused selection is made up of fish that are both endangered and also valued culturally for many communities.
"To illustrate, the tiger of the river is an symbolic fish of the Himalayas. Numerous people in that area cherish that fish for cultural and spiritual practices that extend well past financial values," commented a freshwater expert who worked on the report.
Similar to other fish on the list, it is experiencing two primary dangers: overfishing and loss of home.
"Environmental degradation includes things like obstructions that break up a waterway, and can disrupt the normal water flow of a river, which results in fish not being able to access their spawning areas," the expert said.
Obstruction to migration is an issue that is especially common in Europe, where fish face a blockage to their paths every kilometre.
Frequently the obstructions are minor culverts or weirs that are unnecessary and could be removed, said an conservation charity head.
But the cumulative effect on migratory fish is enormous: "It can have a massive impact in terms of the strength fish are consuming to pass the [barriers]."
That leaves them more susceptible to illness. They're more prone to get predated. They will breed in suboptimal areas."
Back from the Brink
The majority of fish will cross national boundaries on their lengthy migrations. This requires coordinated efforts between states to address these issues and ensure the recovery of local stocks, explained a study lead author.
The international conservation agreement is a international United Nations agreement signed in 1979 which commits countries to collaborate to safeguard migratory species of every type.
The UN is now recommending that the thirty priority species be added to the treaty at its yearly meeting in the near future.
The distinctive antelope is an example of a species that has profited from being protected under the treaty.
Following a population crash, an international conservation team was established and since then population levels have increased substantially.
"The focus has often been on some of the more well known species, such as large mammals," commented a high-ranking UN representative.
The official noted it was now the time of migratory freshwater fish to receive similar protection.
