Fish species that undertake massive journeys through rivers, lakes, and ponds are grappling with a combined threat from human-made barriers, contaminants, and excessive harvesting preventing them from arriving at their breeding grounds.
Examples including the Himalayan mahseer and giant devil catfish are among 30 priority species which have now been recommended for worldwide conservation by the United Nations in a latest report.
"Freshwater fish support countless numbers of individuals worldwide, so for societies, they're very important," explained a contributing researcher on the assessment.
A group of international experts examined over 15,000 types of migrating freshwater species – which represent 50% of all fish species – and discovered their abundance had declined by an estimated 81% in the past 50 years.
The scientists said that for too long, this group of species has been neglected but "represent an essential part of people's livelihoods."
Overfishing and Habitat Loss
The focused selection is made up of fish that are both at risk and also culturally significant for global societies.
"For example, the tiger of the river is an iconic fish of the Himalayan region. A great many communities in that area value that fish for traditional and sacred reasons that go far beyond monetary values," noted a freshwater specialist who contributed to the study.
Like many fish on the list, it is experiencing two primary dangers: excessive fishing and habitat loss.
"Habitat loss involves things like obstructions that divide a waterway, and can alter the normal water flow of a river, which causes fish not being able to connect to their spawning areas," the spokesperson said.
Interruption to migration is an problem that is especially common in Europe, where fish encounter a barrier to their paths on average every 0.6 miles.
Frequently the obstructions are small culverts or weirs that are redundant and could be removed, noted an environmental charity head.
But the combined effect on migratory fish is immense: "It can have a massive impact in terms of the energy reserves fish are using to navigate the [barriers]."
That makes them more prone to illness. They're more prone to get hunted. They will spawn in suboptimal areas."
Road to Recovery
Most species will cross national boundaries on their extensive journeys. This requires collaborative actions between governments to tackle these threats and secure the rebounding of national populations, argued a study lead author.
The international conservation agreement is a global United Nations agreement signed in 1979 which requires nations to cooperate to conserve migratory species of many kinds.
The UN is now recommending that the 30 priority species be included to the agreement at its annual conference in the coming years.
The Saiga antelope is an example of a species that has seen improvement from being listed under the treaty.
Following a mass die-off, an global conservation initiative was created and since then population levels have recovered substantially.
"The focus has clearly been on some of the more charismatic species, such as whales," said a senior UN official.
The official added it was now the opportunity of river fish to gain from similar efforts.
