Revisiting safe biological limits in fisheries

Fisheries management reference points used for stocks in the Northeast Atlantic were investigated as to the appropriateness of their current levels based on three practical limits of exploitation in fisheries management: (i) the smallest sustainable size of the fished stock (SSBpa), (ii) the maximum sustainable rate of exploitation (Fmsy), and (iii) the age at maturity, i.e., the smallest body size of captured fish that still allows for individual reproduction. SSBpa is a widely used reference point for low population size. In 46% of the examined stocks, the official value for this reference point was found to be below the consensus estimates determined from three different methods. Additionally, the natural rate of mortality M is widely regarded as an upper limit for sustainable fishing pressure (Fmsy) that can produce the maximum sustainable yield (MSY). However, the official estimates of Fmsy exceeded the rate of natural mortality in 76% of the stocks. Finally, there is wide agreement that age at maturity is a lower limit for age at first capture. However, age at first capture was below maturity in 74% of the stocks. No official estimates of the stock size (SSBmsy) that can produce MSY are available for the Northeast Atlantic. However, an analysis of stocks from other areas confirmed that twice SSBpa provides a reasonable preliminary estimate. Using this proxy with Northeast Atlantic stock sizes in 2013 showed that 88% were below the level that can produce MSY. Also, 54% of the stocks were outside of safe biological limits and 12% were severely depleted. Fishing mortality in 2013 exceeded natural mortality in 72% of the stocks, including those that were severely depleted. These results point to the urgent need to re-assess fisheries reference points in the Northeast Atlantic in order to implement the regulations of the new European Common Fisheries Policy regarding sustainable fishing pressure, healthy stock sizes and adult age/size at first capture.