Inter-benchmark Protocol for sole in the Eastern English Channel (IBPsol7d).

Type Article
Date 2019
Language English
Author(s) ICES
Contributor(s) Girardin RaphaelORCID, Ball Johnathan E., Spence Michael A., Sys Klaas, Vansteenbrugge Lies
Source ICES Scientific Reports/Rapports scientifiques du CIEM (2618-1371) (ICES), 2019 , Vol. 1 , N. 75 , P. 88p.
DOI 10.17895/

The ICES Inter-Benchmark Protocol of sole in the Eastern English Channel stock (IBPsol7d) met to investigate the effect of the missing UK beam trawl commercial index (UK-CBT) in 2017 and 2018, that was related to the recent change in the database system in UK. The aim was to inves-tigate the internal consistency of the new UK-CBT and to analyse its influence on the sole in 7d assessment. The model currently used to assess this stock is an extended survival analysis (XSA). No other model was tested. During the IBP, it was decided to revise the Belgium beam trawl commercial index (BE-CBT) to move from a Landing Per Unit of Effort (LPUE) index to a Catch Per Unit of Effort (CPUE). This decision was motivated by the increase of age 2 sole discards in recent years, and also to investigate the feasibility of adding a second index to tune age 2 sole in the assessment and put UK-BTS survey index into perspective.

The IBP investigated alternatives to calculate both new commercial indices. In the old UK-CBT a 10% threshold of sole in the landings was applied to select the vessels used in that index. The IBP decided to remove that threshold to produce the new UK-CBT, assuming that all beam trawl-ers using an appropriate mesh size have some sole in their bycatch. The new BE-CBT now in-cludes both small and large fleet segments in addition to the discard information. A vessel effect is applied to standardize the new BE-CBT index. Both indices were calculated using mixed GLMs.

Several assessment settings were tested, replacing each new index one at a time. The IBP agreed to use the new UK-CBT and the new BE-CBT in the assessment of this stock. However, the age 2 sole in the new BE-CBT were removed, as the residual pattern of the model at age 2 was consid-ered too high by the IBP (absolute value of 2 or above in a log-scale). The diagnostics of the assessment were considered good enough to use the assessment as the basis for advice in 2019, although some unresolved issues with input data remain. The final XSA assessment run included the revised UK-CBT and the revised BE-CBT, as well as the FRA-COTB as commercial tuning series, and the UK BTS, FRA-YFS and the UK-YFS as survey tuning series.

New reference points were estimated following ICES guidelines. FMSY analyses were conducted with Eqsim.

Short-term forecast assumptions were investigated. Based on the retrospective pattern of the re-cruitment estimates, the IBP decided to replace the two last years of recruitment by a geometric mean.

Future research and the need for a full benchmark were identified, also by the external reviewer.

Full Text
File Pages Size Access
Publisher's official version 86 5 MB Open access
Top of the page