Which is worse for the oceans - eating meat or eating fish?

It's a commonly-encountered sentiment amongst people who care about oceans: many marine ecosystems are in trouble; fisheries are a primary cause for much of this trouble; ergo, to help the ocean a person should stop eating fish.

This seems like a fairly straightforward argument. However, it gets murky very quickly if the person replaces seafood with meat from terrestrial production systems. Consider this: the UN FAO estimates that 18% of global greenhouse gas (GHG) emissions are attributable to livestock production. Read that again - 18% of all anthropogenic GHG emissions are associated with livestock production. This is more than the share attributable to transportation. (Read the FAO brief here).


This is primarily due to the methane produced by ruminants (cattle, sheep, and goats), the carbon emissions associated with the land use practices that support livestock production, and nitrous oxide emissions from the use of synthetic nitrogenous fertilizers and the use of manure (download source here). Carbon dioxide emissions associated with the production of synthetic nitrogenous fertilizers and farm-level processes also figure in.

Beef is far and away the worst offender. Much of the reason is due to the methane that cattle produce - as a greenhouse gas, methane is 23 times more powerful than carbon dioxide, and cattles' byzantine digestive systems produce copious amounts of the stuff. As a result, approximately 19 kilograms of carbon dioxide equivalent are produced for every kilogram of beef, according to Ulf Sonesson, an expert in such matters at the Swedish Institute of Food and Biotechnology. And it's not just eee-vile feedlot beef that is to blame: while the issue is quite contentious, it does not appear that halo-wearing grass-fed beef offers any substantial improvement -- it's more likely that it's actually worse than feedlot beef, in terms of GHG emissions.

And this is just GHG emissions. The crops required to sustain livestock production are dependent upon huge amounts of synthetic nitrogen fertilizer. Among the many environmental impacts of synthetic nitrogen fertilizer, perhaps the worst is its role in creating oxygen-starved "dead zones" when enters oceans.

So, we've just seen a brief review of the mountains of evidence showing that meat production has a host of major environmental impacts (and for full disclosure: I grew up on a sheep farm in rural Ohio and I've got nothing at all against farming or livestock production. Nor am I a vegetarian). And we've only looked at the ways that meat production can impact oceans - we've not even begun to look at its massive impacts in terms of land use, fresh-water pollution, use of antibiotics and growth hormones, etc. etc.

Let us return to the initial question: which is worse for the oceans - eating meat or eating fish? Consider that climate change, ocean acidification, and creeping ocean dead zones are three major threats to marine ecosystems worldwide. And consider that meat production is a huge contributor to climate change, is the raison d'etre for much of the world's fertilizer-heavy crop production, and also, through carbon dioxide emissions associated with land use and fertilizer production, likely is a significant contributor to ocean acidification (since ocean acidification is caused by carbon dioxide, methane produced by livestock doesn't figure in).

What about fisheries, though? Don't they use lots of energy and produce lots of emissions? Well, yes and no. While fisheries have been estimated to account for more than 1% of the world's oil use, certain gears are enormously efficient - in fact, purse seine fisheries for small pelagic species such as herring and sardines can be among the most efficient animal protein production systems in the world. Here's a figure that I threw together that compares different food production systems based upon the 'energy return' that we get on our investment of fossil fuel - basically, it shows the percentage of our energy investment that we get back. Note - this does NOT indicate emissions - it only compares "energy out" to "energy in". It does not compare emissions associated with each one - hence, the methane associated with beef production, for example, is not represented in any way, so it would be vastly incorrect to say that beef and scallops have similar 'carbon footprints'. This figure is just a rough sketch of relative energy efficiencies, nothing more. 

Energy return on investment (EROI) of various food production systems,
expressed as % of fossil fuel energy input that we recover in edible protein energy. Sources below.

 So for the ocean-conscious consumer, which is it? I don't have the answer and because it requires comparing apples (climate change, dead zones, ocean acidification) to oranges (marine biodiversity, habitat, food webs, etc), it ultimately is a judgment call. However, I do think that it is clear that the answer to the question is not nearly as obvious as it would seem on the surface.  Eating small pelagics from healthy stocks and well-managed fisheries, for example, presents a very enticing way to obtain animal protein while minimizing the factors that contribute to climate change, ocean acidification, and ocean dead zones.

The take home message? Our food choices are enormously important, for one: your choice to eat meat (or not) is a major determinant of your personal environmental impact.

Finally, if I were forced to do so, I would personally say that the best food choices that we can make for our oceans are:
 1. Ditch unsustainable seafood
 2. Ditch meat except for special occasions
 3. If you don't want to be vegan, replace much of your meat and dairy intake with fish caught in ecologically sustainable and energy-efficient fisheries - such as purse seine-caught sardines or herring.

Arguments? Ideas? Politely-worded hate mail? Let 'er fly in the comments below!

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Abbreviated sources for the EROI figure (leave a comment if you want the full citation): 
Pelletier and Tyedmers, 2007: farmed salmon, wheat
Pelletier, 2008: Soybean, corn, boiler poultry
Pimentel, 1996: Shrimp (Thailand)
Pimentel, 1997: Lamb, swine, turkey
Pimentel, 2004 (in Pelletier, 2008): Beef
Tyedmers, 2000: Salmon (Canada gillnet)
Tyedmers, 2001: Scallops, shrimp (Canada), groundfish, herring (Canada)
My thesis: Herring (U.S. purse seine and pair trawl) and lobster