EU request to provide guidance on the most appropriate method to aggregate species within species groups for the assessment of good environmental status for MSFD Descriptor 1

ICES advises the use of two frameworks for aggregating indicators to species group level:

i) First, combining indicators within each Marine Strategy Framework Directive (MSFD) criterion across all species; second, combining the criteria within each species group (criteria approach).

ii) First, combining indicators within each species across all MSFD criteria; second, combining across species within each species group (species approach).

ICES advises using a criteria approach to aggregation of indicators for the species-rich ecosystem components fish, birds, and cephalopods, and a species approach for the species-poor ecosystem components mammals and reptiles.

ICES advises on appropriate methods (proportional, averaging, conditional) to combine information at each stage of aggregation.

ICES has not been requested to advise on methods to aggregate species groups to assess ecosystem components.