Publication Abstract

Multi-annual TACs and minimumbiological levels

P. Marchal and J.W. Horwood

ICES hasfocused attention on minimum biologically acceptable levels (MBALs) as a basis forensuring the safety of stocks and providing advice for management. Simultaneously theEuropean Commission has proposed the use of multi-annual management strategies. This studymodels the effect of TACs, set constant for different periods of years, on the levels andvariability of spawning stock biomass (SSB) and yield. The Celtic Sea cod is used as anexample. It is shown that, even with annual updating of TACs, target SSBs have to besubstantially greater, possibly more than seven times the MBAL, to avoid the risk ofstocks falling below the critical level. Even if the stock is allowed to fall below theMBAL for 5% of the time, the target stock sizes need to be 3-10 times the MBAL if TACs areupdated at 2-10 year intervals. As the period of stable catches is increased the problems of safeguarding the stock from falling below the MBAL also increase, and stability has tobe paid for by lower target fishing mortalities. Specifically for the Celtic Sea cod, abalance of high yield and safety could be achieved with average catches of 7900 t and atarget spawning stock biomass of 30 000 t.

Reference:

P. Marchal and J.W. Horwood, 1995. Multi-annual TACs and minimum biological levels. ICESJournal of Marine Science, 52: 797-807.