Benchmark workshop 3 on the development of MSY advice using SPiCT (WKBMSYSPiCT3)

Benchmark workshop 3 on development of MSY advice using SPiCT (WKBMSYSPiCT3) is the third effort to provide MSY advice for stocks previously assessed as category 3 stocks. Ten stocks, were initially included in the ToRs, pertaining to four ICES Assessment Working Groups (WGNSSK, WGDEEP, WGBFAS, and AFWG), were selected based on the availability of appropriate data and network capacity. Due to unexpected circumstances, Flounder (Platichthys flesus) in Subarea 4 and Division 3.a (North Sea, Skagerrak, and Kattegat) was not dealt during the meeting. Stock assessments using the stochastic Surplus Production in Continuous Time (SPiCT) model were successful for seven demersal finfish stocks:

1. Greater silver smelt in subareas 1, 2, and 4, and in Division 3.a;
2. Norway lobster in Division 4.a, Functional Unit 32;
3. Cod in Subarea 2 between 62°N and 67°N;
4. Dab in subdivisions 22–32;
5. Flounder in subdivisions 26 and 28;
6. Flounder in subdivisions 22–23;
7. Blackspot sea bream in Subarea 10.

For Turbot in subdivisions 22–32 and Blackspot sea bream in Subarea 9, several model configurations were tested, but the available data did not allow distinguishing between very different, yet equally plausible stock status states and/or the models failed to produce ac-ceptable diagnostics tests. Thus, the SPiCT models were not considered to be valid for providing advice and those two stocks should be assessed using category 3 methods for the time being.

WKBMSYSPiCT3 considered that those stocks with an accepted SPiCT assessment model, the current category could be upgraded since the methodology is appropriate to determine stock status and a short-term catch forecast. However, for Greater silver smelt in subareas 1, 2, and 4, and in Division 3.a, and cod in Subarea 2 between 62°N and 67°N, if the models should be used to provide catch advice, WKBMSYSPiCT3 recommends that a lower fractile of F_MSY is used, specifically a 15th fractile is recommended in order to account for the uncertainty of those two models.

For Blackspot sea bream in Subarea 9, it is recommended that information gathered in the southern part of Division 9 (around Gibraltar) are not included in the assessment of this stock unit but used for Blackspot sea bream in GSA 1, which is assessed by GFCM.

For flounder in subdivisions 22-23 and dab in subdivisions 22-32 it is recommended that catch and survey data from the (southern) Kattegat (Subdivision 21) should be tested for inclusion into the respective stocks in the Baltic Sea. Data evaluation during the benchmark suggests a strong connection between these areas and it is likely that the (southern) Kattegat flounder and dab are part of the larger stocks in the Baltic. The Kattegat is currently assessed as part of the North Sea by WGNSSK.

The extensive exploration of input data and model configurations carried out during the workshop resulted in several recommendations regarding the standardization of commercial CPUE, including approaches accounting for spatial, target and technological creep effects and SPiCT model settings. Finally, for stocks where it was not possible to develop a SPiCT model, the use of integrated models was explored, and it might be considered as an alternative in future to account for the good amount of length and biological information available for these stocks. This is especially relevant to proterandric hermaphroditic species as Black spot sea bream for which the development of an integrated model is recommended for the next benchmark.