Estimation de la mortalite totale du Merlu

Type Rapport scientifique
Date 1973
Langue(s) Français
Référence CIEM CM 1973/G:7
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Auteur(s) Guichet Roger1
Affiliation(s) 1 : Centre de recherches de l'I.S.T.P.M., 74 Allée du Mail, F-17000 LA ROCHELLE, France
Editeur CIEM
Note Comité des poissons de fond (sud)
Résumé en anglais

In this paper the instantaneous total mortality coefficient for hake is estimated., using c.p.u.e. data of La Rochelle deep-sea trawlers from 1968 to 1970. The following two methods are used to calculate the mortality coefficient Z: the first one is obtained with the c·.p.u.e. of two successive year classes for the same year, the second is estimated with the c.p.u.e. of one year class taken in two years rurming. Everywhere, except for the West Ireland area, the total mortality seems to decrease with the age of the fish. Such a result was not observed with the "Thalassa" experimental data in the Bay of Biscay. This suggests a change in fish catchability with age. Generally, there is no great difference between the results of the. two methods. Nevertheless on the west coast of Ireland the first estimate is exceptionally low (Z6-9 = 0.29) whereas the second one is 0.61, a value nea.rer the others. The difference may suggest a declining reoruitment west of the British Isles. Moreover, the fact that a total mortality coefficient as important as the one in the Bay of Biscay is co-existing with a greater number of old hake in the catches make us wonder to what extent these old fish might come from southern areas. The results for the Celtic Sea (0.70), the Bay of Biscay (0.62) and the northern Spain (0.53) are coherent.

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