August 3, 2015 — There’s a saying in fisheries, loosely based on a phrase by the scientist John Shepard, that managing fisheries is just like managing a forest, except the trees are invisible and keep moving around. It’s no surprise then that there’s a lot of confusion about the state of global fisheries. In this post I’ll try to dispel some of this confusion by addressing some common misconceptions, and in doing so talk about some of the research I and others at the Bren School have done in this area.
Fisheries are often talked about in the context of disaster, collapse, and crisis (e.g. this recent post in the Economist). What does the science really tell us though? Let’s take a close look at two of the most common references used to support the claim that global fisheries are in poor shape. Chances are you’ve heard something to this effect: “Global fisheries will collapse by 2048″. This incredibly persistent statement can be traced back to a 2006 paper by Boris Worm and several others titled “Impacts of biodiversity loss on Ocean Ecosystem Services“. They used a database of fishery catches as their indicator of overfishing, marking a fishery as “collapsed” if catches dropped below 10% of the highest catches ever recorded for that fishery. Using this metric, they an increasing trend in the number of collapsed fisheries over time, and noted as a thought experiment that if that trend continued, 100% of fisheries would be collapsed by 2048. This prediction of a future without fish gained a tremendous amount of attention, and is still commonly reported in the media.
This predicted collapse of global fisheries was strongly criticized and largely rejected within the fishery science community on the basis of two major problems. First, Worm’s prediction relies solely on catch data. The reported amount of fish caught in a season can decline for many reasons besides declining abundance, such as changes in reporting criteria, implementation of regulations that change how fish are caught, or shifts in consumer demand. More reliable data on the biomass of fish in the oceans did not reflect the trends of increasing numbers of fisheries collapses seen in the catches alone. Second, the prediction of 100% fishery collapse ignored some important economics. If more and more fisheries were collapsing, the costs of fishing should rise as fish become more scarce. For most species, this would result in a decrease in fishing effort well before the fishery is driven to extinction, albeit at overfished population levels (though some species such as bluefin tuna may respond differently, with prices increasing faster than costs as the species becomes rarer).
Read the full story at the Bren Research Blog