The Status and Potential of Europe’s Atlantic Fisheries
This is the second installment looking at the status and potential of European Atlantic fisheries. In Part 1 we looked at the status and potential of 174 stocks assessed by the scientific process of ICES.
Costello et al. 2016 estimated the status of most of the fish stocks of the world and their prospects under alternative management regimes. This was a statistical method that, while unreliable for any specific stock, appears to provide reliable estimates on average and is used for stocks where groups like ICES have not been able to perform a formal stock assessment. There are some considerable differences in the stocks included in this analysis so the total potential yield is less. For each taxon represented in the FAO catch data base, where possible, they estimated the current yield, the potential yield under perfect management, and the current status in terms of fishing pressure and stock size relative to that which produces long term maximum yield. As their analysis is broken down by stock in the RAM Legacy Database, or by country when the FAO catch data are used, 772 individual “stocks” are estimated. Figure 1 shows the history of stocks for FAO area 27, the NE Atlantic, which constitutes most of the European fisheries catch and projected total yield up to 2050, if each stock was harvested with the exploitation rate that produces maximum sustainable yield. 2012 yield was about 5.5 MMT and it is estimated that with optimal fishing mortality total yield could rise to about 8.0 MMT.
But a key question is where does this increased yield come from? To understand this we have to look at the current status of stocks, shown in Figure 2.
In this graph, each circle represents an individual stock in Atlantic Europe. The area of the circle is proportional to the maximum sustainable yield of the stock and the shading represents what fraction of potential long term yield would be obtained under current fishing pressure. So we see relatively few large stocks, and many very small stocks. The 22 largest stocks account for 80% of the potential yield.
The X axis is the abundance of the stock relative to the level that would produce MSY, and the Y axis is the fishing mortality relative to that which would produce MSY. The vertical and horizontal lines separate the graph into four quadrants. In quadrant A fishing pressure is less than would produce MSY and abundance is higher than would produce MSY. The large red circule located in the lower right corner for instance is the sandeel stock in the North Sea that is estimated to be at 2.5 times the biomass that would produce maximum sustainable yield and is fished quite lightly. Quadrant B is where stock size is below BMSY, but fishing pressure is lower than would produce MSY. Quadrant C is the region of most concern, where fishing pressure is too high and abundance too low.
Stocks in quadrant C and D would produce more long term yield if fishing pressure is reduced, those in quadrants A and B would produce more long term yield if fishing pressure was increased. Stocks in quadrant B will need to rebuild to achieve their full potential but would rebuild if fished at higher fishing pressure.
The future scenario in Figure 1 was setting U/Umsy to 1 for all stocks.
So we see that most of the data, and especially most of the larger stocks are In quadrants A and B. The one large stock in quadrant C – the large stock of most concern in the graph is the North Sea Cod, which was fished much too hard in the assessment used in the Costello et al. paper, but the fishing pressure has been reduced considerably so that using the ICES stock assessments, that stock is now has a U/Umsy of 1.2 so it will be producing over 90% of its MSY at current fishing pressure. Another large stock in quadrant B is Atlantic horse mackerel, which has also seen major reduction in fishing pressure since the assessments used in the Costello paper.
As we did in Part 1, we can look at how much yield would be obtained at current fishing pressure, and how much could be obtained by fishing stocks in Quadrants C and D less, and Quadrants A and B harder.
This is shown in Figure 3.
As we saw in Part 1 using the ICES assessment data, there is more potential yield from stocks that are currently fished at rates less than U/Umsy than to be gained by reducing pressure on stocks fished harder than U/Umsy, but to obtain maximum long term yield both would need to happen.
The same caveats to this analysis apply. Specifically this assumes that each stock could be managed independently to achieve Umsy, and that there are no ecological interactions between stocks. Both of these would likely lead to there being less potential yield than calculated.
Figure 4 shows the same results as Figure 3 as a pie chart.