Monday, July 11, 2011

Farming the sea

The cover story in this week's issue of Time Magazine tackles the pros and cons of farming fish, a subject that gets suprisingly little solid media coverage in North America. Bryan Walsh's article does a decent job covering the decline of the world's fisheries, and the need for solutions. But like so many articles on the subject, it buries what should be the lede:

Especially troubling, many of the most popular farmed species are carnivores, meaning they need to be fed at least partly with other fish. By one count, about 2 lb. of wild fish ground up to make fish meal is needed on average to produce 1 lb. of farmed fish, which leaves the ocean at a net loss.

I've written about this before: A substantial proportion of the wild harvest is used to maintain marine aquaculture of carnivorous species like salmon. It is wildly inefficient, the marine equivalent of farming wolves rather than herbivorous cattle. This is why many experts conclude that the future for pescetarians is probably the blander, lower-on-the-food-chain species like tilapia and catfish.

In coverage of aquaculture, we tend to focus on the sexier and scarier subjects: pollution from farms, genes mixing with the wild population, PCBs in farmed salmon, etc. Certainily, no doubt, these are all serious concerns (except perhaps the PCBs). But the feed-to-fish ratio is the very core of the matter; if you get less fish protein out than you put in, aquaculture doesn't make a heck of a lot of sense.

Walsh gets to this central dilemma in the second half of the article:

When producers began raising fish intensively, they picked species that people like to eat: salmon and sea bass. But those species are high on the food chain, and raising them on a farm is a bit like trying to domesticate tigers. [ed - nice. I always say wolves] The aquaculture industry has gotten better at replacing fish meal with plant-based feed, but not fast enough. You're not feeding the world sustainably if you need to remove the base of the marine food chain to do it. 

The solution that many propose is expanding the use of plant-based products in fish food. That brings it's own complications. For one, salmon certainly didn't evolve eating soymeal, cornmeal or wheat, so shifting to a majority plant-based diet will likely involve further genetic engineering, which has supporters and detractors. 

And second, feeding plant products to fish would add another player in the struggle for the world's productive croplands. 

Forget food vs. feed. Or food vs. fuel. In the future, it will be a battle of the 4 Fs:  food vs. feed vs. fuel vs. fish.


Hank Roberts said...

Great to see you take up this topic.

Fish oil replacement in finfish nutrition

Giovanni M. Turchini,
Bente E. Torstensen,
Wing-Keong Ng

Article first published online: 10 FEB 2009

DOI: 10.1111/j.1753-5131.2008.01001.x


Unsustainable fishing practices have placed a heavy emphasis on aquaculture to meet the global shortfalls in the supply of fish and seafood, which are commonly accepted as the primary source of health-promoting essential omega-3 (n-3 highly unsaturated fatty acids). However, dietary fish oil is required for the production of omega-3-rich farmed fish and this commodity, in a vicious circle, is at present derived solely from wild fisheries ...."

Yes, plant source food can be fed to fish. No, it doesn't work the same way. Major challenge there.

Simon Donner said...

The next question is producing the plant-based oils to replace fish oil in aquaculture feed. The Turchini paper offers some perspective on the numbers; oil production from plants (soybeans, palm trees) is an order of magnitude greater than fish oil production (from catching wild fish). Switching to more plant-based feeds may hold some promise, but we need to look at more production scenarios. It'd be a good graduate research project for someone!