One of the main sources of error affecting ageing precision is the discrimination bet-ween the false ring and annulus. An ageing process follows a number of typical steps. First, an ageing methodology is established, based on scientific information, to obtain age data for a particular species. Once age results are available, some analysis is re-commended to improve precision among different readers and/or readings. The next step is to perform other studies that offer independent results used to support, or not, an accepted ageing methodology. Several matching and independent results help to corroborate certain ageing criteria. Each study determines how precision and/or trueness are enhanced. In general, these methods are included in indirect or semi-direct validation categories, as true ages are not actually known in any of them. Some other methodologies, usually more complex and costly, are considered strictly as validation experiments, as results approach to real ages. Tagging-recapture experiments and rearing in captivity are included within this category.
The latest available information on ageing data (precision and/or validation studies) was presented for a number of different species of small pelagics. Methods highlighted included marginal increment analysis (MIA), marginal analysis (MA), length frequency distribution analysis (LFDA) and back calculation (BC). A synthesis table of the last annual growth workshops and exchanges by species is also presented. The goal, for each species (Engraulis encrasiculus, Sardina pilchardus, Clupea ha-rengus, Sprattus sprattus, Scomber scombrus, Scomber colias, Trachurus trachurus, Trachurus mediterraneus, Trachurus picturatus, Micromesistius potassou), was to add information on the exchange or workshop and to present the major difficulties that caused low Percentage of Agreement between the age readers as well as to recommend some guidelines to overcome those difficulties.
Given that several methods exist for validation of age readings of calcified structures, a summary table of age validation methods used for all small and medium pelagic species in European waters was developed with a focus on the feasibility for the small pelagic species and validation strength of the folowing methods: BC, LFDA, Weight frequency distribution (WFD), Progression of strong year-classes, MIA, MA, daily growth increments (DGI), Daily increments widths, Tagrecapture analysis and Captive rearing.
|Publisher||International Council for the Exploration of the Sea (ICES)|
|Number of pages||83|
|Publication status||Published - 2020|
|Series||ICES Scientific Report|