Fonteneau Alain. (2014). Tentative sequential population analysis of Indian Ocean skipjack catch at size. In :
16ème groupe de travail sur les thons tropicaux. Victoria : CTOI, 11 p. (Documents de Réunion ; IOTC-2014-WPTT16-50). GTTT : Groupe de Travail sur les Thons Tropicaux, 16., Bali (IDN), 2014/11/15-19.
Titre du document
Tentative sequential population analysis of Indian Ocean skipjack catch at size
Année de publication
2014
Type de document
Colloque
Auteurs
Fonteneau Alain
In
16ème groupe de travail sur les thons tropicaux
Source
Victoria : CTOI, 2014,
11 p. (Documents de Réunion ; IOTC-2014-WPTT16-50).
Colloque
GTTT : Groupe de Travail sur les Thons Tropicaux, 16., Bali (IDN), 2014/11/15-19
This paper is attempting to do a simplified sequential population analysis of skipjack CAA based on 2 average CAS estimated during the 2004-2013 period (original and corrected ones), and assuming various levels of natural mortality at age. It was first noticed that when the estimated CAA is showing a very low apparent total mortality between the various ages estimated by slicing (using the Eveson & al 2014 growth curve), the life expectancy of tagged skipjack recovered is very short, showing an apparent total yearly mortality estimated at about 2.0. As a result of this basic inconsistency between CAA and natural mortality, all ASP have been providing totally unrealistic results, estimating very low fishing mortality exerted at all ages. An ad hoc analysis of the recovery data has been done, and it is showing that skipjack growth rates appear to be highly variable between individuals. If this result is confirmed by further statistical analysis, it would mean that there is a very poor relationship between skipjack sizes and ages, medium & large sizes skipjack being probably dominated by young fast growing skipjack, while the old skipjack surviving in the population are probably rare. This question is quite fundamental and its potential consequences in the functioning and results of the SS3 model should be carefully examined.
