Information and data for the application of SPiCT to produce MSY advice for Nephrops Stock in FU 26-27 (Western Galicia and Northern Portugal)

Evaluación de Recursos Marinos Vivos en el Área ICESEVALICES

First steps in the estimation of harvest ratio reference points for Nephrops FU 30 (Gulf of Cadiz)

In 2014, a Benchmark Workshop on Nephrops Stocks (WKNEP) was planned for 2016 with a data evaluation meeting in June 2016 and the Benchmark meeting in October 2016. This WD shows the preliminary work carried out till the date about the Nephrops FU30-specific Harvest Ratio reference points estimation

NEW PROPOSED AREA FOR THE ISUNEPCA UWTV SURVEY IN THE GULF OF CADIZ (FU 30)

ISUNEPCA UWTV survey is carried out in the Gulf of Cadiz (UF 30) yearly in spring-summer since 2014, although the first survey is considered as exploratory. The main objective is to estimate a Nephrops abundance index to be use as base of the assessment and advice of this stock. The Nephrops area distribution and coverage of the survey was accepted by the Benchmark Workshop WKNEP in 2016 and this survey was considered as appropriated to providing scientific advice on the abundance of this stock. However, experience acquired during ISUNEPCA survey time series suggests the survey area should be smaller than the current coverage area for this UWTV survey. Therefore, the Nephrops abundance estimate and as consequence the advice of this stock could be affected. A new survey area is proposed based on the analysis of updated and available data

ISUNEPCA0721 UWTV Survey on the Gulf of Cadiz Nephrops Grounds and catch options for 2022 in FU30

This working document details the results of the underwater television survey on the Gulf of Cadiz Nephrops grounds (FU 30) conducted in 2021. The survey is considered multi-disciplinary in nature, collecting UW videos, CTD and dredges information. A total 65 UWTV stations were planned in a randomized 4 nm isometric grid but only 59 UWTV stations were used in the geo-statistical analysis. The mean burrow density observed in 2021, adjusted for cumulative correction factor, was 0.024 burrows/m². The final krigged abundance estimate was 73 million burrows with a CV of 11.5%. The 2021 abundance estimate was the lowest value recorded in the time series. Catch advised for 2022 in FU30 when the ICES precautionary approach is applied and according to category 3.1.4, was no more than 50 tonnes

Final report of the Working Group on Nephrops Survey (WGNEPS)

WGNEPS es un grupo de coordinación de Grupos de Expertos en campañas de arrastre y de imágenes submarinas dirigidas a la estimación de la abundancia de Neprhops en el área ICES y de forma exploratoria en el Mediterráneo

Solving optimal control problems with non-smooth solutions using an integrated residual method and flexible mesh

Solutions to optimal control problems can be discontinuous, even if all the functionals defining the problem are smooth. This can cause difficulties when numerically computing solutions to these problems. While conventional numerical methods assume state and input trajectories are continuous and differentiable or smooth, our method is able to capture discontinuities in the solution by introducing time-mesh nodes as decision variables. This allows one to obtain a higher accuracy solution for the same number of mesh nodes compared to a fixed time-mesh approach. Furthermore, we propose to first solve a sequence of suitably-defined least-squares problems to ensure that the error in the dynamic equation is below a given tolerance. The cost functional is then minimized subject to an inequality constraint on the dynamic equation residual. We demonstrate our implementation on an optimal control problem that has a chattering solution. Solving such a problem is difficult, since the solution involves infinitely many switches of decreasing duration. This simulation shows how the flexible mesh is able to capture discontinuities present in the solution and achieve superlinear convergence as the number of mesh intervals is increased