Small Scale Otolith Exchange for North East Atlantic Mackerel (Scomber scombrus) 2014
Atlantic mackerel (Scomber scombrus) is a pelagic species of high commercial importance in European waters. Living on both sides of the North Atlantic ICES currently uses the term “Northeast Atlantic (NEA) mackerel” to define the mackerel present in the North East Atlantic with a distribution range from the Iberian Peninsula in the South to the Nordic Sea including Icelandic and Greenland waters and the Western Baltic. Recent ICES stock advice based on an age-based analytical assessment model shows that the stock of NEA mackerel is on a very high level.
Age readings on mackerel are important input data for the assessment and carried out by a number of laboratories using international agreed ageing criteria. However, the report on the latest workshop on age reading of mackerel (WKARMAC, ICES 2010) stated that the frequency of workshops and exchanges on age reading of mackerel in the past was far from impressive. The first reported workshop on mackerel ageing was held in Lowestoft in 1987 and following that only one workshop has been held (in 1995 in Spain) and one additional exchange in 2002. All previous workshops and exchanges have had an outcome stating the overall agreement to be low but fair, but skewed towards having a higher agreement on the younger ages. All workshops discussed and made an effort to standardize age reading methods by preparing a manual and a reference collection of agreed age otoliths.
The overall result of the last exchange and workshop exercise in 2010 was that there were significant variations in mackerel age estimates between readers. Low precision, and large relative biases between readers were found, and the older ages (from age 6) were particularly difficult to reach agreement upon. Following these findings all participants in the workshop agreed to follow the guidelines of the WKARMAC report for the decided upcoming exchange of images to facilitate an evaluation of the guidelines. This short report represents the results of this exchange summarizing the readings of 19 readers of 10 European laboratories in nine countries. The exchange was carried out from December 2013 to April 2014.