Dam building binge in Amazon will shred ecosystems scientists warn


first_img Sign up for our daily newsletter Get more great content like this delivered right to you! Country LIMA—Once upon a time, thousands of dorados, a giant among catfish, would swim more than 3000 kilometers from the mouth of the Amazon River to spawn during the austral autumn in Bolivia’s Mamoré River, in the foothills of the Andes. But the dorado, which can grow to more than 2 meters in length, is disappearing from those waters, and scientists blame two hydropower dams that Brazil erected a decade ago on the Madeira River.”The dams are blocking the fish,” says Michael Goulding, a Wildlife Conservation Society aquatic ecologist in Gainesville, Florida, who has been studying the dorado since the 1970s. They are “probably on their way to extinction” in Peru and Bolivia.Most Amazon dams are in Brazil, where scientists have raised concerns about the displacement of local communities and emissions of greenhouse gases such as carbon dioxide and methane from large reservoirs. But as countries seek new energy sources to drive economic growth, a surge in dam construction on the eastern flank of the Andes could further threaten fish migration and sediment flows, Elizabeth Anderson, a conservation ecologist at Florida International University in Miami, and colleagues warn today in Science Advances. Dam building binge in Amazon will shred ecosystems, scientists warn By Barbara FraserJan. 31, 2018 , 2:00 PM E. ANDERSON ET AL., SCIENCE ADVANCES, EAAO1642 (2018) ADAPTED BY J. YOU/SCIENCE Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe During the rainy season—from November to May—water levels rise in the Amazon Basin, flooding large tracts of forest. Various species of fish swim into the forest, where they feed on fruits—and later disperse seeds. By blocking migration routes or changing water levels, dams change seed dispersal patterns, says Sandra Bibiana Correa, a freshwater ecologist at Mississippi State University in Starkville. The fish-forest pas de deux “is a really delicate interaction,” she says. “It has been going on for tens of millions of years. We can disrupt that very easily.”Some species are taking advantage of the disorder. Another kind of giant catfish known as the manitoa or piramutaba once rarely ventured upstream of rapids that predated the Madeira River dams. Unlike its cousin, this species (B. vaillantii) can make it through both dam bypasses and into the upper reservoir, and from there swims another 1000 kilometers or so upstream to Peru’s Madre de Dios watershed. Whether the newcomer will fill the dorado’s ecological role or prey on different fish and thus skew species assemblages is unclear, says Carlos Cañas, a river ecologist at the Wildlife Conservation Society here, who plans to monitor the migration of large catfish in the watershed.Two other threats—climate change and the deforestation that accompanies road building during dam construction—could amplify the severity of ecological deterioration, Anderson says. At stake, she says, are the livelihoods of indigenous peoples who depend on fishing. Other projects, such as Peru’s plans to dredge rivers to improve navigability, could exacerbate the ecological impact by changing flows, disturbing spawning sites, and disrupting the river-forest connection, says Fabrice Duponchelle of the French Institute of Research for Development in Marseille.Amazon nations should work together to craft a basin-wide management plan for migratory fish, says Thomas Lovejoy, a tropical ecologist at George Mason University in Fairfax, Virginia. “You have to manage the Amazon as a system,” he says. It’s not too late to preserve much of the ecology of the western Amazon Basin, where “we still have a lot of free-flowing rivers,” Anderson adds. “There is a huge opportunity to protect at least a subset of them by thinking at a regional scale.” Email Catches of dorado are in decline as the catfish is failing to navigate two dams on its epic spawning run. MICHAEL GOULDING Parting the waters A new analysis forecasts severe habitat fragmentation in the western Amazon Basin if some of the 160 planned dams are built in the region, where 142 dams are already. For the ecology of the western Amazon Basin, where the mountains meet the lowlands, the main consequence of proliferating dams is habitat fragmentation. Interference with spawning is one facet. Another is that dams hold back sediments and nutrients that nourish the Amazon Basin, Anderson says. Her team documented 142 hydropower dams that are operating or under construction on headwaters in the western Amazon Basin, and another 160 that are under consideration. If even a fraction of the planned projects is completed, the habitat disruption could have a cascade of ecosystem effects with devastating consequences, scientists say.The disappearance of the dorado (Brachyplatystoma rousseauxii) from the Mamoré River suggests fragmentation is already taking a toll. And that’s despite features of the dams that are meant to mitigate their impact. The Madeira dams, for example, are designed to allow fish to pass: The lower dam has a bypass channel and the upper dam has an enclosure in which fish are captured. They are then trucked upstream for release into the reservoir. Perhaps because of variations in currents or water chemistry, dorados are not using the channel, says Carolina Rodrigues da Costa Doria, an ichthyologist at the Federal University of Rondônia in Porto Velho, Brazil. The threat may not be limited to fish: Freshwater dolphins and river otters may also migrate along Amazonian rivers, and how dams affect their behavior is unknown, says Paul Van Damme, director of the Institute for Applied Research on Water Resources, a research center in Cochabamba, Bolivia. Click to view the privacy policy. Required fields are indicated by an asterisk (*)last_img

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