WKWEST - Report of the Benchmark Workshop on West of Scotland Herring (WKWEST)

The WKWEST meeting was held in the Marine Institute, 80 Harcourt Street, Dublin, Republic of Ireland, 2–6 February 2015, to benchmark the assessments of herring in VIaN and VIaS, VIIb,c (or alternatively VIa, VIIb,c combined) and the Celtic Sea, VIIg,j. The data compilation process and intercessional work began in October 2015. Previous assessments of these stocks applied the Integrated Catch Analysis (ICA) model. The 2014 Benchmark Workshop on Pelagic Stocks (WKPELA) changed the assessment model for Celtic Sea VIIg,j herring to the State-space Assessment Model (SAM). However, WKWEST concludes that the Age Structure Assessment Program (ASAP) offers an improved fit to recruitment signals than SAM for Celtic Sea VIIg,j herring. In the case of VIaS, VIIb,c both analytical and non-analytical assessments had suggested this stock was extremely low, but the exact size of the stock is uncertain. For all stocks in the VIa, VIIb,c region, the mixing of the stocks and doubt as to whether the two stocks can be accurately identified in both the catch and survey data persisted as a major source of uncertainty.