Benchmark workshop on Pandalus stocks (WKPRAWN)

Benchmark results

Northern shrimp (Pandalus borealis) in divisions 3.a and 4.a East (Skagerrak and Kattegat and northern North Sea in the Norwegian Deep)

An ensemble model was developed to incorporate uncertainty in natural mortality (SS3 model). A distribution of possible natural mortalities at age was constructed based on a suite of M life history and other type models. Three M scenarios were developed: a low, median and high M. An objective weighting approach was used based on model performance statistics and diagnostics to develop the final assessment. The reference points were estimated using a shortcut MSE approach testing a range of fishing mortalities and biomass thresholds in relation to virgin stock size (B0). 

Northern shrimp (Pandalus borealis) in subareas 1 and 2 (Northeast Arctic)

For the Barents Sea stock, the accepted assessment model fell on SPiCT. The commercial CPUE used in the assessment was thoroughly investigated and standardized using a non-spatial model. A spatio-temporal modelling approach (sdmTMB) for the joint Norwegian/Russian Barents Sea Ecosystem Survey (BESS) was presented and compared to the design-based estimators currently used. There was some retrospective error on F/Fmsy but Based on the presented diagnostics, the reference model was considered adequate and acceptable. The standard approach for short-term forecasts and reference points was agreed.

Flemish Cap shrimp (NAFO Div. 3M)

There was limited progress on the Flemish Cap stock (pra.27.3M). An excellent long-term EU survey from 1988-present is available for the stock covering the period of the moratorium. This shows an increase from 2016 to 2019 with a subsequent decrease. Length-composition data are also available from the survey for this assessment. In future, it may be possible to explore an SS3 model for this stock given the partial and patchy nature of the available data.