Second Workshop on Stock Identification and Allocation of Catches of Herring to Stocks (WKSIDAC2)

Population identification plays an important role in the assessment of Atlantic herring (Clupea harengus). Several morphological/traditional methods have been applied in the past to split catches (both within survey and commercial samples) and to identify herring populations. However, in recent years advances in genomics have provided a robust and precise method to genetically identify herring populations. WKSIDAC2 reviewed the current status of genetic population identification for herring and outstanding issues affecting identification accuracy/success. The genetic methods using single nucleotide polymorphism (SNP) as genetic markers to identify herring population are considered appropriate. Depending on the region of interest, different sets of markers are used to identify herring populations. The differences in the set of markers have only minor influence on the population identification and can be negligible. However, it is recommended to choose sets of markers which will allow a direct comparison between institutes undertaking the classification. Furthermore, the review concluded that 26 different herring spawning populations can be currently identified using genetic methods in the northeastern Atlantic. However, future genetic studies may increase the number of identified populations and also provide a greater resolution for the spatial distributions. For example, from the genetic markers presented during WKSIDAC2, we are not able to genetically differentiate between Icelandic summer spawners, Faroese autumn spawners, and Norwegian autumn spawners. These three populations are currently combined as a single genetic unit. Future work incorporating whole genome sequencing data, is recommended to investigate this issue in more detail. In addition, of the 26 identified genetic populations only some can directly and uniquely be assinged to a particular stock (management unit) and for this reason WKSIDAC2 refrained from establishing such correspondence which is left for future work. Baseline samples of these 26 populations have been analyzed based on different sets of markers. Therefore, the baseline information cannot be shared directly between institutes. Also, it is recommended that a common method for analyzing baseline samples, as well as storing the genotypes in an open and public database is agreed. During WKSIDAC2, a general description of prerequisites for the implementation of population identification of herring was discussed and several options have been presented. A series of presentations provide potential solutions on how to implement population identification in current stock assessment models or during survey estimates. However, analyses of the optimal baseline requirements for stock assessment purposes, both for specific surveys as well as commercial catches is to be the subject of a new workshop WKSIDAC3, proposed for 2024. The aim of the workshop is to establish a simulation framework for estimating stock compositions based on genetics 1) to investigate differences between random or stratified sampling, and 2) to investigate inter-haul variability in surveys.