Are natural and fishing mortalities comparable for tropical tunas ? : a multispecies approach with tagging data

Abstract : With the aim of increasing the precision of parameter estimates in tagging analyses, we assumed that the dynamics of tagged fish from different tropical tuna species have processes in common. With this consideration in mind we fit different data sets from two distinct periods of the eastern Atlantic fishery with a multispecies tag-attrition model to provide information for the shared parameters. Among the different assumptions considered, a common attrition rate for the three species of tropical tuna (yellowfin, skipjack and bigeye tuna) was not supported by the data under the AIC criteria. However the estimates of the attrition rate for yellowfin and for skipjack were relatively close. On the basis of these preliminary results, it would be interesting to check in the future the accuracy of a common type-1 tag losses (i.e., α) between tagging periods/locations or between species with more complete data sets. Given the limitations of the data and accounting for model uncertainties, it was shown that the Z coefficient was increased by a factor 4.5 for yellowfin from the first period of time (1980-1981) to the second one (1996- 2002). For skipjack and bigeye tuna this increase reached 3.4 and 3.2, respectively. One explanation may result from the increasing use of FADs fishing operations in the tropical surface fishery.
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Collective Volume of Scientific Papers, ICCAT, 2006, 56 (2), pp.421-430
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Daniel Gaertner, François-Xavier Bard, Jean-Pierre Hallier. Are natural and fishing mortalities comparable for tropical tunas ? : a multispecies approach with tagging data. Collective Volume of Scientific Papers, ICCAT, 2006, 56 (2), pp.421-430. 〈ird-00351392〉

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