The populations of migratory freshwater fish are “collapsing”, having declined by about 81% since the 1970s, one of the largest drops ever recorded among the major groups of vertebrates on the planet.
The alert is issued in a report published this Tuesday and presented at the 15th Global Summit of the United Nations Convention on Migratory Species (CMS COP15), which is taking place in the city of Campo Grande, Brazil.
Therefore, some of the longest and most important migrations of freshwater fish, fundamental to the proper functioning of rivers and the ecosystems that depend on them most, as well as to the livelihoods of various human communities, are at risk and in rapid decline.
The analysis speaks of a “largely overlooked biodiversity crisis” and identifies 325 species that must be urgently protected through international efforts, namely through their inclusion in the Appendices of the Migratory Species Convention: 205 from Asia, 55 from South America, 42 from Africa, 50 from Europe and 32 from North America.
Among the main rivers that should be targeted for protection to curb the decline of freshwater migratory fish are the Amazon and La Plata in South America, the Danube in Europe, the Mekong in Asia, the Nile in Africa and the Ganges in Southeast Asia.
Based on an analysis of the conservation status of nearly 15,000 freshwater fish species, the report, whose lead author is Zeb Hogan, a professor at the University of Nevada, United States of America, and also known for his wildlife documentaries, concludes that 97% of the 58 migratory fish species listed by the convention (including freshwater and saltwater) are threatened with extinction.
“Many of the world’s great wildlife migrations happen underwater,” says Hogan. “This assessment shows that freshwater migratory fish are in grave danger and that protecting them will require countries to work together to keep rivers connected, productive and teeming with life.”
Great rivers of South America at risk
The CMS COP is taking place this year in Brazil, whose government, host of the meeting, is proposing several conservation measures to protect life in the Amazon and La Plata.
The Amazon basin is considered one of the last great refuges for freshwater migratory fish, but the intensification of human pressures, such as infrastructure development, is threatening this refuge.
A case study published alongside the report reveals that 20 migratory fish species in the Amazon are eligible for inclusion in Appendix II of the convention, which includes species with unfavorable conservation statuses and whose conservation requires international cooperation.
It is in the Amazon as well that lives one of the world’s largest migratory fish, and which does not exist anywhere else: the catfish species Brachyplatystoma rousseauxii. With a body of metallic tones and silvery and golden reflections, this fish can grow to up to two meters in length, and makes one of the greatest migrations of all freshwater fishes: it travels about 11,000 kilometres from the Andes to nursery areas on the coast.
Brazil is also proposing listing Pseudoplatystoma corruscans in Appendix II, a species that lives in the La Plata but is threatened by barriers such as dams, by changes in current flow and by increased fishing pressure.
For all this, and because they know no borders, experts argue that rivers should be managed as ecological systems rather than as national and isolated waterways.
“This new assessment highlights the conservation of migratory species and their habitats as a fundamental priority, which, to date, has not received due attention,” states Amy Fraenkel, executive secretary of the United Nations Convention on Migratory Species.
“By aligning science, policies and international cooperation, governments can safeguard the great freshwater fish migrations that still remain in the world, as well as the communities and ecosystems that depend on them,” warns.
