A recent report explains that people in Bangladesh fulfill their daily nutrients from consuming small fish from rivers. Photograph by Tanvir Ibna Shafi

NAGOYA, Japan, Oct 22, 2010 (IPS) – Damming a river may bring electric power, but it often comes at the price of high-quality food fisheries, experts say. When dams are proposed for power, flood control or irrigation, the often devastating impacts on fisheries in rivers and lakes are ignored or discounted.“It is very difficult to put a dollar value on what inland fisheries represent because it is much more than the landed value of the fish at the dock,” says Yumiko Kura of the WorldFish Center office in Phnom Penh, Cambodia.

Kura is co-author of a new report, “Blue Harvest: Inland Fisheries as an Ecosystem Service”, which highlights the wide-ranging importance of inland fisheries in diets, especially among children, and not just in terms of protein but in supplying micronutrients, notably vitamin A, calcium, iron and zinc.

“Detailed studies in Bangladesh for example have shown that daily consumption of small fish contributes 40 percent of the total daily household requirement of vitamin A and 31 percent of calcium,” according the report released Friday at a side event at the 10th Conference of the Parties to the Convention on Biological Diversity.

In addition, it notes there are more than 60 million full- and part-time jobs in fishing and other activities such as processing, with over half these jobs carried out by women.

A river system like the Mekong is amongst the most productive fisheries in the world largely because there are few dams, and it retains most of its wetlands, Kura told IPS. Fishers in the Mekong catch more than 500 species of fish – its very diversity sustains the health of the river, and some 22 million people in Cambodia and Laos who depend on the Mekong’s bounty.

By contrast river systems in developed countries are near biological deserts with few species, according to a landmark study published in the journal Nature earlier this month. Paradoxically, rich countries employ vast quantities of concrete for energy and flood control, decimating rivers’ natural abilities to control and clean water and provide food, according to the first ever study of the world’s river systems.

“What made our jaws drop is that some of the highest threat levels in the world are in the United States and Europe,” Peter McIntyre, a co-author of the Nature report and zoologist at the University of Wisconsin-Madison in the U.S., told IPS in a previous story.

Fish also serve as important links between ecosystems. The nutrients and organic matter from fish eggs, carcasses and excretion help to support the production of algae, insect larvae and other fish species in rivers and lakes, says the “Blue Harvest” report compiled by the U.N. Environment Programme (UNEP) and the World Fish Centre.

When fish populations decline, there can be serious knock-on effects for other organisms, said Jacqueline Alder, head of marine and coastal ecosystems at UNEP. Widespread mortality of the cisco fish from Lake Mendota in the U.S., for example, led to changes in the plankton composition of the lake, decreased the level of nutrients in the water column and caused a decline in the biomass of algae.

“Unlike oceans, inland waters are highly vulnerable and changes can come very quickly,” Adler told IPS.

The report warns that despite over 40 years of steady production globally, rapid environmental changes are occurring which challenge the viability of future fish stocks and a range of internationally-agreed development targets including the Millennium Development Goals.

Dams, unsustainable agriculture and large removals of water for industry, along with pollution and wastewater discharges, have significant impacts on river systems, the report found.

Japan used to have productive inland fisheries but there are very few left, almost entirely due to development, says Kura, who is from Japan. Many of the country’s rivers were lined with concrete in the past two decades in a short- sighted attempt to control flooding and maintain transport channels. Rivers need to be able to flow to the sea, with shoreline vegetation and wetlands to keep them healthy and productive, she said.

Major cities in China’s Yangtze River valley such as Chongqing, Nanjing, Shanghai are adding 25 billion tonnes of wastewater to the river annually, much of it untreated. Along with other factors, such as dams and over-abstraction of water, pollution is linked with a decline in Yangtze fish catches. The Chinese sturgeon and the Chinese paddlefish are now classed as critically endangered.

Fish catches in Africa’s Lake Malawi and Lake Malombe and in the Niger River have fallen as a result of dam building and environmental degradation. Between 40 and 50 percent of rivers in Asia, Africa and Latin America are undammed, but less than 12 percent of large European rivers have water flow unaffected by dams, the report shows.

The Pak Mun dam, built on a tributary of the Mekong River in Thailand in the early 1990s, triggered a 60 to 80 percent fall in fish catches. Proponents said the new reservoir created by the dam would produce 220kg/hectare of fish, but this only reached 10kg/hectare.

Since 2001, a seasonal flooding policy involving opening the dam gates has been adopted, helping to bring back close to 130 species to the Mun River and reducing the impact of the dam on fisheries.

However, other dams are being proposed on the Mekong, says Kura. The full value of the river’s fisheries is difficult to assess and the value of the landed catch is all that’s being considered. The impacts on jobs, food security, culture, healthy and the region’s biodiversity aren’t properly considered in regional development plans focused on energy and irrigation, she said.

“We need to value all the components in the river’s watershed, the landscape and the water work together as one system,” Kura said.

Stephen Leahy is a freelance journalist. He can be contacted at steve.leahy0@gmail.com. Or follow him on Twitter at http://twitter.com/StephenLeahy