Dated, Erroneous Assumptions Yield Misleading 'Carbon Footprint' For Farmed Shrimp
Global Aquaculture Alliance
A presentation by ecologist J. Boone Kauffman of Oregon State University at the 2012 meeting of the American Association for the Advancement of Science has led to a series of sensationalized and misleading articles about the impacts of shrimp farming.
While the Global Aquaculture Alliance does not dispute Kauffman's concerns about the carbon footprint of converting mangroves to other uses, GAA challenges his assumptions regarding the role of shrimp farming in such conversions.
Kauffman reached carbon footprint values that are not applicable to the vast majority of shrimp aquaculture practiced today, Global Aquaculture Alliance President George Chamberlain said. Only about 3 percent of the current global farmed shrimp production is raised under the conditions on which Kauffman based his calculations.
Kauffman's briefing paper said that 50 to 60 percent of shrimp farms are constructed in former mangrove areas, have annual productivity of just 50 to 500 kilograms per hectare and are abandoned in just three to nine years. By combining these erroneous assumptions, he concluded that the release of carbon dioxide through conversion of mangrove land to shrimp ponds yields a 198-kilogram footprint per 100 grams of edible shrimp.
"It is important to understand how far off those numbers are," Chamberlain said.
In research with World Wildlife Fund's Jason Clay, aquaculture scientist Claude Boyd estimated that less than 10 percent of historic mangrove loss resulted from shrimp farm construction. The practice of converting mangrove areas to shrimp ponds essentially stopped almost two decades ago due to strong regulatory and industry pressure. The main causes of mangrove loss are agriculture, salt evaporation ponds, mining and infrastructure development.
Although common in the 1980s, low-density culture methods as described by Kauffman are currently confined to limited areas of Bangladesh, Indonesia and southern Vietnam, and now represent only a few percent of the total global shrimp harvest.
It is inaccurate to assume that shrimp ponds have a lifespan of three to nine years, Dan Lee, GAA Best Aquaculture Practices standards coordinator, said. While shrimp farms built in mangrove areas are inherently inferior to higher-elevation ponds due to acid sulfate soils and limited drainage, they become less problematic over time as the acid gradually neutralizes. Mangrove ponds in Ecuador and Honduras are still in operation after 40 years, and traditional "tambak" ponds have produced fish and shrimp in Indonesia for hundreds of years.
"While the Global Aquaculture Alliance supports Kauffman's valuation of mangroves as important ecological carbon sinks that should be conserved, we take issue with his calculations about shrimp farming," Chamberlain said. "His assumptions bear little relation to today's shrimp-farming industry, which has long since moved away from the mangrove zone. It's akin to calculating soil erosion for U.S. agriculture based on the Dust Bowl practices of the 1930s."
Kauffman's numbers were quickly distributed by various media entities, often within articles with anti-shrimp headlines. In addition, some inattentive editors incorrectly reported his data and claimed that only 1 kilogram of shrimp is produced in 13.4 square kilometers of pond -- an absurd statistic.
"“It is very unfortunate that these misleading messages are being circulated," Lee said, "GAA sincerely hopes that when consumers and others read such material, they can recognize how outdated and distorted it is."
Estimating Global ‘‘Blue Carbon’’ Emissions from Conversion and Degradation of Vegetated Coastal Ecosystems
Linwood Pendleton 1. , Daniel C. Donato 2*., Brian C. Murray1, Stephen Crooks3, W. Aaron Jenkins1,Samantha Sifleet4, Christopher Craft5, James W. Fourqurean6, J. Boone Kauffman7, Nu´ ria Marba`8,Patrick Megonigal9, Emily Pidgeon10, Dorothee Herr11, David Gordon1, Alexis Baldera12.
Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems—marshes, mangroves, and seagrasses—that may be lost with habitat destruction (‘conversion’). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this ‘blue carbon’ can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15–1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3–19% of those from deforestation globally, and result in economic damages of $US 6–42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of landuse conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the wellrecognized ecosystem services of coastal habitats.
1 Nicholas Institute for Environmental Policy Solutions, Duke University, Durham, North Carolina, United States of America, 2 Ecosystem & Landscape Ecology Lab, University of Wisconsin, Madison, Wisconsin, United States of America, 3 ESA Phillip Williams & Associates, San Francisco, California, United States of America, 4 United States Environmental Protection Agency, Research Triangle Park, North Carolina, United States of America, 5 School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana, United States of America, 6Department of Biological Sciences and Southeast Environmental Research Center, Florida International University, North Miami, Florida, United States of America, 7 Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, United States of America and Center for International Forest Research, Bogor, Indonesia, 8 Department of Global Change Research, Mediterranean Institute for Advanced Studies, Esporles, Illes Balears, Spain, 9 Smithsonian Environmental Research Center, Edgewater, Maryland, United States of America, 10 Conservation International, Arlington, Virginia, United States of America, 11 International Union for the Conservation of Nature, Washington, District of Columbia, United States of America, 12 The Ocean Conservancy, Baton Rouge, Louisiana, United States of America Fuente: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3433453/pdf/pone.0043542.pdf
Links de interés
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