Working group on surveys on ichthyoplankton in the North Sea and adjacent seas (WGSINS; outputs from 2023 meeting)

The Working Group on Surveys on Ichthyoplankton in the North Sea and adjacent Seas (WGSINS) coordinates surveys on fish early life stages undertaken for assessment and management purposes. The objectives of WGSINS include review and coordination of these surveys, quality assurance on survey methodology, species identification, provided data and indices, preparation of data for archival, as well as identification of additional objectives that can be achieved by the surveys.

WGSINS coordinates seven surveys, three in the North Sea (IHLS - International herring larvae surveys in the North Sea, MIK - North Sea Midwater Ring Net survey, DRS - Downs recruitment survey), two in the Irish Sea (NINEL - Northern Irish Northeastern Larvae Survey, NI-MIK - Northern Ireland MIK Survey) and two in the Baltic (RHLS - Rügen herring larvae survey, BIS - Baltic Ichthyoplankton Surveys). Most surveys target herring larvae from various stocks, while the NI-MIK targets pelagic juvenile gadoids and the BIS eggs and larvae of Eastern Baltic cod.

At WGSINS 2023, cruise summaries and results from the seven surveys were presented. All relevant estimates and indices from the surveys were updated, and data were uploaded into the ICES eggs and larvae database. New methodologies to incorporate the DRS into the MIK recruitment index time-series were discussed and evaluated, concluding that these can provide improvements to the existing MIK index. However, further refinement is needed before these are presented to the Herring Assessment Working Group (HAWG).

The chair of WGSMART presented updates on the egg and larvae module in SmartDots. WGSINS agreed to provide expertise and support in reviewing documentation and testing of further software developments. Representatives from the ICES Data Centre presented updates to the ICES eggs and larvae database, and introduced the new Fecundity and Atresia Database. A newly established governance group for these two databases, the Working Group for Egg & Larvae and Fecundity & Atresia Database Governance (WGELFADG), was introduced.

WGSINS provides a forum to present and discuss additional work conducted on ichthyoplankton surveys that can provide additional information and data products, such as investigations on non-target ichthyoplankton species, other organisms like jellyfish and zooplankton, or marine litter. Several presentations highlighted the potential of ichthyoplankton surveys to provide added value, improving our understanding of pelagic ecosystems and contributing to stock assessment and management. A pilot study on sandeel larvae identified for example spawning areas in the North Sea which contributed to the re-evaluation of management areas during the recent benchmark workshop on sandeel, while another pilot survey aimed to establish a recruitment index for North Sea sprat. Ideas for other additional sampling opportunities were presented and discussed, such as sampling of cephalopod early life stages to identify spawning and nursery areas.

WGSINS will continue to collect and archive additional information, underrepresented in traditional fishery survey datasets, aiming to contribute to the implementation of an ecosystem approach to fisheries management.