On the growth of bigeye tuna in the Indian Ocean: what is the real age of a 50 cm/2.6kg bigeye?

All stock assessment done by the IOTC WG in 2013 on the Bigeye
stock were done using the Eveson & al 2012 growth curve. This growth curve estimates that 50 cm bigeye are fished at an age of 2 years, suffering a high natural mortality of 0.8 during each of these 2 years. However, the analysis of the bigeye growth rates between 37 and 50 cm, based on 930 mell measured recoveries, strongly indicates that the real age of a 50 cm bigeye would be close to only 1 year (then with only 1 year class suffering a high natural mortality of 0.8). The paper tries to estimates the consequences of this misspecification of the growth model in the stock assessment work: there is no doubt that a corrected growth should be used in future model, but based on the present results, this improved growth should not deeply alter the main conclusion of the 2013 assessment models, for instance the trajectories in the Kobe plot).