Tuesday, February 16, 2010

Sustainability and Global Seafood

This morning, I continued working through the Food Security special issue of Science by looking at a paper by Smith et al (20 authors in all) entitled Sustainability and Global Seafood.  The paper is rather confusingly organized, and IMO mistitled - "Social Justice and Global Seafood" would have been nearer the mark.  Nonetheless, it is interesting.

The main theme of the paper is summarized in the graph above, which shows, in the top panel, per capita fish consumption by nation.  One of the interesting things is the very high Chinese per-capita fish consumption (for a poor country).  Given the huge population of China, absolute fish demand there must be a very sizeable fraction of global consumption.

In the bottom panel the countries are colored according to a composite of four world bank indicators designed to measure overall governance effectiveness.  This is not governance of fisheries, but overall governance (stuff like corruption, political stability and absence of violence, etc).  I wasn't familiar with these indicators but they look worthy of further exploration in the future (since I'm generally keen to find reliable indicators of the overall political stability of the planet).  The pattern in that data is more-or-less what you'd expect- the developed countries are well governed, places like Russia, China, and Brazil are in the middle of the scale, and poor African countries are a mess.  Then the hatching over the color shows the fraction of the population undernourished (the barely discernable key is not my fault - it's that way in the original image at Science's site, but I think the single direction hatching is 5-15% undernourished, and the hatched-both-ways is >15% undernourished).

Anyway, the pattern here is more or less what you'd expect also - poor government and a lot of hungry people are strongly correlated.

The paper then goes on to try to make the argument that poor, badly governed places are particularly likely to be fish exporters.  The presentation of the data here was somewhat confusing to me - a simple scatterplot would have made the situation very clear, but instead they have a table of countries by region that makes it harder to tell what's going on.  However, the header section of the table is as follows:

The "Low" line is the countries where <5% of the population is undernourished.  They have 29% of the global population, are massive net fish importers, eat a reasonable amount of fish (21.7kg /year is about 15 oz/week), and are mostly fairly well governed.  The "Moderate" line are the countries with 5-15% undernourishment, which hold another 31% of global population, eat a similar amount of fish (but I imagine China is in this group and heavily distorts the statistic), and are net fish exporters.  Finally, the "High" group are the hungry countries with >15% undernourished.  They only eat half as much fish on average, but are exporting a lot of fish.  I guess Somalia is the poster-child for this situation.

I thought a paper with the title "Sustainability and Global Seafood" would be mainly about the status of global fish stocks, but there is not much at all on that. If you actually wanted to know how things were going on that front, you'd be better off reading Worm et al, Impacts of Biodiversity Loss on Ocean Ecosystem Services, from Nov 2006. The following graph is drawn from that paper:

Trajectories of collapsed fish and invertebrate taxa over the past 50 years (diamonds, collapses by year; triangles, cumulative collapses). Data are shown for all (black), species-poor (<500 species, blue), and species-rich (>500 species, red) LMEs. Regression lines are best-fit power models corrected for temporal autocorrelation.

Here LME = Large Marine Ecosystem.

As you can see, the overall trend of global fish stocks is steadily more dismal.


Chris Lawrence said...

Yes, we're essentially killing the oceans through pollution, which is causing dead zones, carbon emissions, which are leading to ocean acidification, overfishing, which is um, leading to no fish, etc. It remains to be seen if we have the will to stop before there is pretty much nothing left.


Nick G said...


Have you posted (or seen) data about the % of calories from seafood?

I'm very curious how much the oceans contribute to overall nutrition.