Example of a stock synthesis projection approach at alternative fixed total allowable catch (TAC) limits implemented for three previously completed north Atlantic shortfin mako stock synthesis model runs

Projections were implemented for three North Atlantic shortfin mako shark Stock Synthesis model runs previously presented to the ICCAT Shark Working Group during the 2017 ICCAT Shortfin Mako Assessment Meeting. Projections resulted in continued short term population declines, regardless of the TAC level, because it took many years for the surviving recruits to reach maturity (female age at 50% maturity = 21 yr) and begin to contribute to the spawning stock size. MCMC Kobe II risk matrix probabilities indicated that projections at a fixed annual TAC limit of between 800 – 900 t resulted in ≥ 50% probability of being in the Kobe green zone (the joint probability of F < FMSY and SSF > SSFMSY) by 2070 (two generations) for preliminary model runs 1 and 2. In contrast, projections at a fixed annual TAC limit of 800 t resulted in the spawning stock size stabilizing below the level required to return the stock to a size that could support MSY by 2070 for model run 3, the base Stock Synthesis model run resulting from the 2017 meeting.