SUMMARY

• Main Authors: D S Butterworth, A E Punt
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.498.4783; http://www.iccat.int/Documents/CVSP/CV054_2002/no_2/CV054020365.pdf

Aspects of previous analyses of North Atlantic bluefin tuna dynamics which take account of trans-Atlantic mixing are discussed. A key matter that requires consideration by the Workshop is the current differing estimates of certain biological parameters for West and East resource components. In particular, growth curves used at present for West and East differ appreciably at larger ages, which means that previous mixing analyses are internally inconsistent in treating some fish of rather different lengths as having the same age. One possible solution to this is to move towards length-based assessments. These might have the additional advantage of simultaneously providing a more reliable basis for modelling the catches of the largest fish than the present influential, though not particularly satisfactory, assumption for West assessments of temporally invariant F10+/F9 ratios. It is suggested that following the development of a limited set of alternative stock structure scenarios, the Workshop should concentrate on the specification of simulation tests to assess the extent to which incorrect assumptions about such structure might bias estimates not only of past and current resource status, but more particularly of population projections for different levels of assumed future catches. RÉSUMÉ