Report of the Workshop on Egg staging, Fecundity and Atresia in Horse mackerel and Mackerel (WKFATHOM)

The Workshop on Egg staging, Fecundity and Atresia in Horse mackerel and Mackerel (WKFATHOM) chaired by Cindy van Damme, Netherlands, met twice in 2015. The first meeting was from 12–16 October 2015 in Hamburg, Germany, to calibrate egg sorting, staging and identification. The second meeting was from 9–12 November 2015 in Bergen, Norway, to calibrate fecundity and atresia estimation and standardize anal-ysis for the DEPM method.The ‘spray technique’ for the removal of fish eggs from preserved plankton samples was again tested and shown to inexperienced participants.

The majority of the time at the workshop was spent identifying and staging mackerel, horse mackerel and similar eggs. The results promoted discussion and highlighted spe-cific problem areas. These discussions led to the further development of standard pro-tocols, and enhancements to the species and stage descriptions. The results were very reassuring and similar to those obtained at the 2012 workshop. For the experts there was an underestimate of stage 1 mackerel eggs (stages 1a and 1b combined) during the first round of analysis (-3%) and (-4%) during the second round. The results for stage 1 horse mackerel eggs reduced from an overestimate of 5% to 3% underestimate. This is particularly reassuring as it is at this stage on which the egg production estimates are based.

The pipette sampling for fecundity samples was again shown to the participants. A trial during the workshop showed that all participants take the pipette samples correct as weight of the samples were close to the assumed weight.

The screening, fecundity and atresia calibration proved beneficial to all participants. Agreement in fecundity estimates is very high. For atresia problems occurred which sparked discussion and improved the description of early alpha atresia stages. After discussion, the manual has been improved and there was agreement on identification of vitellogenic and early alpha atretic oocytes.

POF staging remains difficult, but the plenary session on POF staging clarified the POF stages and assessing POF stage for the whole sample.

As the mackerel and horse mackerel egg surveys are carried out once every three years, these workshops are a refresher for expert survey participants and a first acquaintance with new participants in the sample analyses. It should however be realized that two weeks of workshops are not enough to train new participants. Institutes should allow newcomers to be trained properly before the survey.