Analysis of the potential impact of several management measures for eastern Atlantic bluefin tuna on the basis of yield per recruit

A standard yield per recruit (YPR) analysis is used to analyse the effects of minimum size regulations and time area closures on bluefin tuna from the eastern stock (east Atlantic and Mediterranean). Analyses were based on a fishing mortality vector computed over the period 1990-1994 for which data were more reliable and VPA (performed during the 2002 stock assessment) showed a relatively good convergence. This fishing mortality vector was modified according to some combinations of minimum size regulations and time area closures. It is concluded that: (i) PSmed is the main contributor to catch at age in the range of ages 1-13; (ii) The minimum size regulations considered would increase the YPR more than the time area closures, but these would enhance SPR more than minimum size regulations; (iii) Closing the Mediterranean has a bigger impact on both YPR and SPR than closing the east Atlantic, given that the majority of the catch occurs there; (iv) under some scenarios, some fleets could increase their long term YPR over 100%. On the other hand, some fleets would reduce their short term yield to near 30% with respect their equilibrium yield before implementing the measures discussed in this document.