Report of the workshop on sexual maturity staging of mackerel and horse mackerel (WKMSMAC)

Under the EU Data Collection Regulation, maturity samples are collected for mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus). These data are used for fishery stock assessment and also for different types of studies regarding the maturation cycles of these species. Several different maturity scales are currently used by different institutes. Most of these scales are used for very specific purposes, and the data produced are difficult to compare or jointly analyse. The Walsh scale, in particular, has been used for 17 years, and is used as routine or for special purposes by most of the observers present at the workshop. Taking into consideration the generic standard scale proposed in a previous workshop (WKMAT), and the characteristics of the mackerel and horse mackerel reproductive cycles, the workshop has proposed a standard scale for these species. The Walsh scale was fitted into this standard scale, which was used in the calibration exercises along with the Walsh scale. Ideally a calibration should be carried out with gonads of a ‘known’ stage. For practical reasons such an exercise was not possible. Therefore, the objective of this workshop was restricted to compare and improve the agreement between observers, assuming that the “correct stage” was the one given to each gonad by the majority of the observers.