Report of the Workshop on Age Reading of Mackerel

Type Expertise
Date 2010
Language English
Ref. ICES CM 2010/ACOM: 46
Other localization
Author(s) ICES Advisory Committee on Fishery Management
Contributor(s) Dufour Jean-Louis, Felix Jerome
Sponsor ICES
Abstract The overall result of the exchange and workshop exercise is that there are significant variations in mackerel age estimates between readers. Low precision, and large rela-tive biases between readers were found, and the older ages (from age 6) were particu-larly difficult to reach agreement upon.
The workshop achieved quite a lot in terms of ironing out, through discussion and calibration, some of the major problems in ageing otoliths of mackerel. The group reached agreement on the definition of a set of ageing guidelines. These are men-tioned in the present report, and the aim is to employ these guidelines to eliminate some of the problems with e.g. interpretation of the otolith edge.
The image analysis exercise clarified that the lack of agreement can be mainly attrib-uted to the perception of the otolith edge, depending on season and area of catch.
Exploring the application of image analysis, the group agreed that applying such tools in both exchanges and workshops dealing with mackerel may prove very valu-able. It gives the opportunity to discuss in depth the definition of which age struc-tures to count, and additionally gives a very useful exchange tool for the individual readers to use, both within and between laboratories.
A collection of agreed age otoliths was started at the workshop using the few agreed otoliths from the exchange. The reference collection will be expanded considerably through an ex-change of otolith images performed immediately after WKARMAC. Additionally, the collection of agreed age otoliths should not stand alone, but be a part of a larger compilation of data on ‘typical’ otoliths for the species and area, in which typical distances between age-structures, edge development over season, and general growth curves for mackerel are represented across its area of existence.
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