Validation of the first annual increment deposition in the otoliths of European anchovy in the Bay of Biscay based on otolith microstructure analysis

Abstract

In order to validate the first annual increment deposition in European anchovy otoliths, early juveniles were captured in October 2012 in the southern Bay of Biscay. These individuals were maintained under a continuous feeding regimen in a sea cage over a period of 6 months. From October 2012 to January 2013, lengths increased slightly or remained stable at ~9.8cm. After this period, standard length increased significantly up to a mean value of 12.0cm in April 2013. Likewise, the age of anchovies was estimated based on otolith microstructure analysis. The estimated age varied from 96 days (for individuals sampled in October 2012) to 293 days (for anchovies sampled in April 2013). A daily increment deposition rate was confirmed in otoliths of individuals maintained in the sea cage during the winter. The general otolith daily growth pattern showed that increment widths increased rapidly and were broadest between 51 and 56 days, with a mean of 19.1µm. Thereafter, the widths decreased steadily to 1.5µm and remained almost constant until the end of the experiment. The present study also revealed that the first translucent band formation started in autumn and was completed by spring.