A year-class curve analysis to estimate mortality of Atlantic bluefin tuna caught by the Norwegian fishery from 1956 to 1979

• Main Authors: Fromentin, Jean-marc, Restrepo, Victor
• Format: Article in Journal/Newspaper
• Language: English
• Published: ICCAT 2009
• Subjects: Thunnus thynnus; fishing and natural mortalities; year-class curves; stock assessment; Norwegian Sea; Tangen; Mer de Norvège
• Online Access: https://archimer.ifremer.fr/doc/00192/30294/28783.pdf; https://archimer.ifremer.fr/doc/00192/30294/

At the ICCAT symposium on bluefin tuna that held in Santander in April 2008, Tangen et al.(2009) presented a first quantification of the fishing effort deployed by the Norwegian fishery targeting bluefin tuna in the North Sea and Norwegian Sea. Using a year-class curve analysis on the Norwegian CPUE, this document presents the first estimates of mortality rates of Atlantic bluefin tuna that migrated north from the mid-1950s to the late 1970s. The results indicate that bluefin tuna would have experienced a total mortality rate (Z) of 0.2 to 0.4 yr-1 (i.e. F at around 0.3 yr-1) during the late 1950s, 0.2 yr-1 during the 1960s and 0.1 yr-1 afterwards (assuming M=0.1 yr-1). These results appear to be rather robust and consistent with the VPA estimates from the 1970s and early 1980s, albeit slightly higher. The fishing mortality rates experienced by bluefin tuna in the North Sea and Norwegian Sea during the period 1956-1979 were thus significant (so that local overfishing may have occurred, especially during the 1950s), but lower than F estimated by year-class curve analysis in recent years (i.e. 1992-2004). This comparison between two distant periods of time during which BFT was significantly (highly) exploited tend to confirm, with new pieces of information, the pessimistic conclusions of the 2006 stock assessment. Lors du symposium ICCAT sur le thon rouge qui s’est tenu à Santander en avril 2008, Tangen et al. (2009) a présenté une première quantification de l’effort de pêche déployé par la flottille norvégienne ciblant le thon rouge dans la Mer du Nord et la Mer de Norvège. En utilisant l’analyse des courbes de captures sur cohortes sur les données de PUE norvégiennes, ce document présente les premières estimations de taux de mortalité du thon rouge migrant au Nord entre le milieu des années 1950 et la fin des années 1970. Les résultats indiquent que le thon rouge aurait subi des taux de mortalité totale (Z) de 0,2 à 0,4 yr-1, i.e. F autour de 0,3 yr-1 durant la fin des années 1950, 0,2 yr-1 durant les années ...