On February 17, 2012, Science magazine published a story titled The Carbon Footprint of a Shrimp Cocktail. It was based on a presentation made by Dr. Boone Kaufman, a forest ecologist at Oregon State University, at a meeting of the American Association for the Advancement of Science. The story was widely disseminated by the media. But is the carbon footprint of farmed shrimp as large as the story suggests? Our work suggests it isn’t and that instead farmed shrimps’ carbon footprint is hundreds of times lower.
I am writing to cover two topics: one of my specialties, shrimp aquaculture and its environmental sustainability, and one on the publicity of the media surrounding scientific discoveries.
The basic premise was of Kaufman’s work was that shrimp farms have been developed throughout the world by clearing mangrove forests to produce shrimp at very low levels of intensity (50-500 kg of shrimp per hectare per year), and that the environmental footprint of these systems is massive.
Kaufman stated that these farms make up about 50% of the shrimp production in the world, and that clearing mangroves releases 1,472 metric tonnes of carbon dioxide annually per hectare. Given an assumed five-year lifespan for the shrimp ponds, this production would equate to about 198 kilograms of carbon dioxide released to the atmosphere for each 100-gram portion of shrimp cocktail — the equivalent of burning 90 liters of gasoline!
Obviously, anyone reading media articles produced from these results would be motivated to abstain from shrimp because of this massive effect on greenhouse gases. Websites, such as Treehugger, MSN New Zealand, and Yahoo News (to name just a few) took this information and posted articles about the environmental damages caused by eating shrimp.
There is no doubt that loss of mangroves is a global problem and that shrimp farming has in part contributed to that. Whether you want to eat shrimp or not is a personal decision, one that should be based on factual information. Now let me give you some facts that may shed more light on this issue.
First, most shrimp today are not grown in mangrove areas, but farther inland in areas above the high tide level. This change occurred in the 1990s with the evolution of shrimp culture, due to both concerns about mangrove loss and the fact that modern shrimp ponds must be flushed and drained to function properly, which is not possible in areas that are regularly submerged by tidal flows. In fact, mangrove experts agree that probably about 10% of mangrove losses have occurred because of clearing for shrimp farms. Urbanization, forestry and rice farming are also culprits in these losses.
Second, shrimp today are grown at 60 to 1,400 times higher than the levels of production used by Kaufman in his estimates. That means the carbon emissions produced via shrimp farming are much less than Kaufman’s work suggested. Global statistics on annual yields from shrimp farms are not available, but at University of Michigan we have completed several surveys in Thailand and China on shrimp culture, and virtually all of the farms we have visited use semi-intensive to intensive levels of production, which equate to 7,000 to 30,000 kilograms per hectare per year of annual yield (60 to 1,400 times higher than levels of shrimp production used by Kaufman). China and Thailand together produced 53% of all farmed shrimp in 2010, so those countries define shrimp farming worldwide. Total global production was 3.8 million metric tons (see FAO for aquaculture statistics). While there remains a small component of low-intensity shrimp farming in the world today – of the type used by Kaufman in his work – a generous estimate of that as a portion of the total shrimp produced would be far less than 10% by weight. Another factor to add to this is that such farming is usually for local consumption in poorer countries, while exported shrimp are commonly produced by more intensive methods.
Assuming these two facts are correct, we should not use clearing of mangroves as our sole estimate for shrimp impacts, but rather intensive production using modern export methods. We should also use realistic details on the duration of farming in ponds (far longer than 5 years; most farms have been in existence for 20 years and continue production in the same ponds, while some have abandoned ponds in a few years), as well as the overall impacts of the production cycle to estimate the impact of eating farmed shrimp.
We have used Life Cycle Assessment (LCA) to determine the cradle-to-grave impacts of shrimp farming in China, which includes the energy and material inputs to farm construction, hatchery operations, grow-out farming, processing, transportation to market, and use and disposal by consumers (see article in Environmental Science and Technology by Cao et al.).
Such an analysis gives a much more accurate tracking of the impacts of shrimp culture and the greenhouse gas costs of your shrimp cocktail. Our estimates indicate that the whole life cycle for 100 grams of processed shrimp cocktail produced 0.5-1 kilograms of CO2 – 400 or more times lower than the Kaufman estimate – depending on the production method, with intensive systems having a larger impact than semi-intensive ones. These results were similar to another LCA done by Rhattanawan Mungkung on Thai shrimp. Both have been reviewed by external referees, approved, and published in peer reviewed literature, outside of typical aquaculture journals.
This evaluation begs one to ask a number of questions regarding the hype surrounding the shrimp cocktail presentation. First, why did Kaufman — and for that matter Science — not look at the peer-reviewed literature to determine the relative validity of his estimates, or at least admit that the numbers were likely biased, given the reality of shrimp farming and scientifically peer-reviewed assessments?
This leads to the second part of this post, which is on the validity of science being promulgated by media outlets like those mentioned earlier.
Over the past 50 years, ecology has moved from research done largely at universities, modestly funded by either internal or small external grants and published in fairly narrow journals to inform other scientists, to current work done on sizeable extramural grants and published in far-reaching outlets to influence public policy and decisions. This is not necessarily bad — in fact, the need for scientists to promote their work to the public is greater than ever, given the need for unbiased information to guide public policy — but it is bad when the material promoted does not reflect the scientific thoroughness the public should demand.
The media’s interest in science and distortion of scientific claims is a major problem in understanding scientists’ role in the world. It has led to publication of books for scientists on how to get more public recognition for their work (see Escape from the Ivory Tower: A Guide to Making Your Science Matter). As for Science and Nature, there have been evaluations questioning the objectivity of these journals and asking whether they more often publish articles because they are controversial rather than because they are accurate (see article by Dr. Ray Hilborn from University of Washington).
I cannot answer this fully. What I can say is that a group of prominent aquaculture scientists collaborated to write a brief but fact-filled response to the Shrimp Cocktail release. We submitted it to Science and asked for it to be included with their press release. They refused, telling us we could list it as a public comment on their website, but nothing more. So at least in this case, Science appeared uninterested in trying to help readers better evaluate the accuracy of their claims regarding shrimp as a food item.
Finally, let’s get back to your shrimp cocktail. If you accept my worst estimate of 1 kilogram of CO2 per 100 grams of shrimp, then how does shrimp compare to other hors d’oeuvres?
Similarly sized portions of buffalo wings would produce about the same CO2 emissions as shrimp, while tenderloin sliders or pork empanadas would liberate more CO2 (7-9 kilograms) in their production. For evaluated systems of farmed seafood, shrimp are the most greenhouse gas intensive, while salmon or tilapia are lower in their impact on climate change. This is the correct way to look at these impacts, by using a comparable and comprehensive analysis of the environmental burdens in production, and by comparing it to other food choices. Of course, there are other impacts beyond greenhouse gas emissions, like energy use or water use.
Different production methods can also result in major differences in the environmental impact of a food product. Free-range chicken or beef would differ from that produced in CAFOs, just as intensive or semi-intensive shrimp, or even wild-caught shrimp, all result in different impacts. This adds confusion to our questions on what food to eat, but as knowledgeable consumers, they are the sorts of questions we should be asking. In addition, reputable journals should be aiding consumers in answering these questions by providing objective, informed analysis of these impacts.
Bottom line: Which is best for environmentally conscious consumers: shrimp cocktail or buffalo wings? They are about the same. Earlier in 2012, a story circulated widely about CO2 emissions caused by eating shrimp grown in mangrove forests. The story was based on Boone Kaufman’s estimates of shrimp grown in mangrove forests and on a story in Science called The Carbon Footprint of a Shrimp Cocktail. However, our estimates indicate suggest carbon emissions 400 or more times lower than the Kaufman estimate, depending on the production method. Our results are similar to those of Rhattanawan Mungkung on Thai shrimp. Both have been reviewed by external referees, approved, and published in peer reviewed literature. So why did the public hear a different story?
James S. Diana is Director of the Michigan Sea Grant College Program and Professor of Fisheries and Aquaculture at the School of Natural Resources and Environment (SNRE) at University of Michigan. He, his colleagues including Elizabeth LaPorte, and students are studying the Great Lakes. They research a variety of natural ecosystems, focusing mainly on native species, particularly pike and muskellunge. Dr. Diana has studied the behavior and ecology of temperate fishes for three decades, working extensively on the behavior and ecology of many temperate fishes, including pike, muskellunge, brown trout, lake sturgeon, yellow perch, largemouth bass, and alewives. They have also developed interests in aquaculture’s potential contribution to the global food supply through the understanding of ecologically sensitive aquaculture practices, particularly in developing countries.