maandag 8 juli 2013

Confusing Nemo (1): How much is too much?

The Black Fish, an environmental NGO, has made an animation movie on fisheries. Laudibly, the organisation provides the sources for its (albeit not all) claims. I agree with some statements they make, but not all. Let me go through some of them one by one in a series of posts. Number one:
"The global fishing fleet hauls in 80 million tonnes of sea food"
The latest FAO report on the State of the World's Fisheries and Aquaculture (SOFIA) on this states that the amount of fish captured in marine areas is indeed around 80 million tonnes each year. I suspect, however, that this only includes the recorded landings: figures on discards and illegal landings are probably too shaky to be included in these figures. So catches might actually be higher.

So the 80 million tonnes seems accurate, but is it much? For comparison: FAOSTAT states that the world produced almost 300 million tonnes of meat in 2011. But that says little about whether 80 million tonnes (or perhaps more, due to discards and illegal landings) is too much. The most widely used benchmark for this is maximum sustainable yield (MSY). The SOFIA does that, and concludes that around half of evaluated stocks is fully exploited (around MSY); overexploited stocks (stocks that, in the report's definition, "produce lower yields than their biological and ecological potential", due to low stock abundance) make up about 30% of the stocks evaluated. Of the remaining 20% harvests can be increased sustainably. What the report also says is that
The declining global catch over the last few years together with the increased percentage of overexploited fish stocks and the decreased proportion of non-fully exploited species around the world convey a strong message – the state of world marine fisheries is worsening and has had a negative impact on fishery production.
In other words, the fact that slowly the number of overexploited stocks is increasing while catches stabilize or decline should, according to the FAO, be taken as a bad sign.

If you want a second opinion, this article by Boris Worm and others should be a good place to start. The authors examined the exploitation rate and biomass of 166 stocks worldwide and found, among others, that
For about two-thirds of the examined stocks (63%), biomass (B) has dropped below the traditional single-species management target of MSY, that is, B < BMSY. About half of those stocks (28% of total) have exploitation rates that would allow for rebuilding to BMSY, that is, u < uMSY, whereas overfishing continues in the remainder (u > uMSY in 35% of all stocks).
That's the bad news. Interestingly, the article also states that
Since the 1990s, Iceland, Newfoundland-Labrador, the Northeast U.S. Shelf, the Southeast Australian Shelf, and California Current ecosystems have shown substantial declines in fishing pressure such that they are now at or below the modeled uMMSY. However, only in the California Current and in New Zealand are current exploitation rates predicted to achieve a conservation target of less than 10% of stocks collapsed.
So is the 80 million cited in Losing Nemo accurate? It seems so. Is 80 million too much? For the short run it also seems so, but on the long term it is more difficult to say. As Worm et al. state, it is still possible to rebuild stocks, and we can only do so by catching less. So far I haven't found any figures on how productive world fisheries stocks could be if we managed them well: 70 million tons? 90 million tons? In any case, things are moving in the right direction as the exploitation rate is slowly declining in most, albeit not all fishing grounds.

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