© 2006 International Council for the Exploration of the Sea
Evidence of underestimation of European hake growth in the Bay of Biscay, and its relationship with bias in the agreed method of age estimation
a IFREMER, Laboratoire de Sclérochronologie des Animaux Aquatiques, STH/LASAA BP 70, F-29280 Plouzané, France
b Laboratoire de Sclérochronologie des Animaux Aquatiques, STH/LASAA BP 70, F-29280 Plouzané, France
c Instituto Español de Oceanografía, Centro Oceanográfico de Vigo Apdo. 1552, 36200 Vigo, Spain
d IFREMER, Laboratoire de Biologie Halieutique, STH/LBH BP 70, F-29280 Plouzané, France
*Correspondence to H. de Pontual: tel: +33 298 224692; fax: +33 298 224653. e-mail: Helene.De.Pontual{at}ifremer.fr.
In 2002, a pilot experiment on hake tagging was carried out using methodology specifically developed to catch and handle fish in good condition. By the end of 2005, 36 hake and five tags had been returned to the laboratory (a 3.1% return rate) with a maximum time at liberty of 1066 days. The somatic growth of the recoveries proved to be twofold higher than that expected from published von Bertalanffy growth functions for the species in the Bay of Biscay. The growth underestimation was related to age overestimation, as demonstrated by two independent analyses. The first was based on a blind interpretation of marked otoliths conducted independently by two European experts involved in the routine age estimation of hake. The result shows that the age estimates were neither accurate (inconsistent with oxytetracycline mark positions) nor precise. The second approach compared the predicted otolith growth with the observed growth, and the discrepancy between the two data sets was large. Both types of analyses invalidate the internationally agreed age estimation method and demonstrate a need for further research. Although based on limited data, the study highlights the need to improve biological knowledge of the species in order to improve assessment and management advice. It also strengthens the argument for age validation.
Keywords: age, age estimation method, age validation, European hake, growth, Merluccius merluccius, otolith, tagging
Received 30 March 2006; accepted 30 July 2006.
1 Present address: University of Bergen, Biology Department, Thormøhlensgt. 55, Bergen 5020, Norway.
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