Limiting inter-annual variation in total allowable catch strategies. An application to ICES roundfish stocks

This study evaluated through simulation management strategy that stabilise catch levels by setting bounds on the inter-annual variability in Total Allowable Catches (TACs). An integrated modelling approach was used, which modelled both the ‘real’ and observed systems and the interactions between all system components. The modelling framework therefore allowed evaluation of the robustness of candidate management strategies to both the intrinsic properties of the systems, and the ability to observe, monitor, assess and control them. Strategies were evaluated in terms of level of risk (measured as the probability of spawning stock biomass falling below the biomass limit reference level for the stock) and cumulative yield. The simulation approach used provides a powerful tool for the examination of the performance of candidate management strategies. It has shown that better management is not necessarily going to be achieved by improving the assessement, since even with a perfect assessment (where the simulated working group knew stock status perfectly) stocks may crash at fishing levels that standard stochastic projections would suggest were safe. Also explicitly modelling the assessment process can result in quite different outcomes than those predicted by the simple projection traditionally used by stock assessment working groups. This is because the simple projection assumes that the status of the stock in the current year is known without error and that the target fishing mortality can be achieved without error. However, in practice the assessment is based on last years data and the effect of any management measure on SSB is only manifest, following the implementation of the quota, at the end of the following year. The choice of target and fishing mortality levels and minimum stock levels results from ICES interpretation of the precautionary approach. This lead to the definition of fishing mortality and biomass reference points that are intended to prevent over-fishing and to trigger recovery plans when a stock is overfished respectively. Although, fishing mortality and biomass reference points were originally intended to be independent, a fishing mortality level implies a corresponding biomass level. In the case of saithe a fishing mortality of 0.40 (i.e. the FPA level) would drive the stock to Blim, suggesting that the choice of biomass and target reference points are not consistent for this stock

Limiting inter-annual variation in total allowable catch strategies. An application to ICES roundfish stocks

This study evaluated through simulation management strategy that stabilise catch levels by setting bounds on the inter-annual variability in Total Allowable Catches (TACs). An integrated modelling approach was used, which modelled both the ‘real’ and observed systems and the interactions between all system components. The modelling framework therefore allowed evaluation of the robustness of candidate management strategies to both the intrinsic properties of the systems, and the ability to observe, monitor, assess and control them. Strategies were evaluated in terms of level of risk (measured as the probability of spawning stock biomass falling below the biomass limit reference level for the stock) and cumulative yield. The simulation approach used provides a powerful tool for the examination of the performance of candidate management strategies. It has shown that better management is not necessarily going to be achieved by improving the assessement, since even with a perfect assessment (where the simulated working group knew stock status perfectly) stocks may crash at fishing levels that standard stochastic projections would suggest were safe. Also explicitly modelling the assessment process can result in quite different outcomes than those predicted by the simple projection traditionally used by stock assessment working groups. This is because the simple projection assumes that the status of the stock in the current year is known without error and that the target fishing mortality can be achieved without error. However, in practice the assessment is based on last years data and the effect of any management measure on SSB is only manifest, following the implementation of the quota, at the end of the following year. The choice of target and fishing mortality levels and minimum stock levels results from ICES interpretation of the precautionary approach. This lead to the definition of fishing mortality and biomass reference points that are intended to prevent over-fishing and to trigger recovery plans when a stock is overfished respectively. Although, fishing mortality and biomass reference points were originally intended to be independent, a fishing mortality level implies a corresponding biomass level. In the case of saithe a fishing mortality of 0.40 (i.e. the FPA level) would drive the stock to Blim, suggesting that the choice of biomass and target reference points are not consistent for this stock

Definition of a directed fishing effort in a mixed-species trawl fishery, and its impact on stock assessments

Catch-per-unit effort (CPUE) has frequently been used as an index of abundance and more specifically to calibrate virtual population analysis (VPA). In multi-species fisheries, CPUE calculated from fishing trips targeting the species seems to be more effective for calibration than the classical ratio total landings/total effort. Target species are determined from an analysis of the composition of catches (landings) of each fishing trip, each trip being categorised as to whether it targets the given species or not. It is obvious that existing but not reported discards would affect these results. Classification of trips can be achieved on a single-species basis, each species being considered successively and each trip possibly being relevant for more than one species. Using a more general approach, classification can be achieved by métiers, each of these being determined by one or a group of target species and each trip being categorised into one and only one métier. This method of categorising trips is based on thresholds of target species contribution to the catch and on an overall explanatory level. For the main species of the French demersal fishery off the west coast of Scotland and in the Celtic Sea, CPUEs are calculated using different methods to define the trips used to calculate fishing effort and associated landings. Besides important differences in actual values, CPUEs may also differ in their trends depending on the definition of directed effort. Tuned VPA, carried out for some species, shows that large variations in population estimates, fishing mortality or short-term predictions could occur when using directed effort, while the catchability model fits the data better

Impact sur le chiffre d’affaires des navires fréquentant la zone de protection de mer Celtique de l’utilisation d’un chalut décollé (dit ‘raised line’)

Le règlement du Conseil de l’UE fixant les TACs et quotas pour 2020 (UE,2020/1231) stipule dans son article 13 qu’aux fins de réduction des captures de cabillaud du stock de mer Celtique, les navires fréquentant la Zone de Protection de mer Celtique (étendue) et capturant plus de 20% d’églefin au cours d’une marée doivent être équipés d’un chalut décollé, dit ‘raised line’ ou de tout autre dispositif permettant d’obtenir une sélectivité équivalente sur le cabillaud

Diagnostic 2019 sur les ressources halieutiques débarquées par la pêche française (métropolitaine)

Ce document a pour objectif de montrer la contribution aux débarquements français des différentes espèces par unité géographique (stocks) en fonction de leur statut au regard de l'objectif fixé par la Politique Commune des Pêches européenne (PCP) et la Directive cadre Stratégie pour le Milieu marin (DCSMM) c’est à dire le rendement maximal durable (RMD) pour tous les stock

Diagnostic 2022 sur les ressources halieutiques débarquées par la pêche française dans les régions ultra-périphériques

Ce document présente la contribution aux débarquements français, en 2021, dans les régions ultra-périphériques (RUPs) des différentes espèces en fonction de leur statut au regard de l'objectif du rendement maximal durable. Ce n’est pas un bilan de santé des ressources halieutiques, mais bien un bilan de l’interaction entre ces ressources et leur exploitation. Beaucoup des espèces débarquées ne font pas l’objet d’une évaluation et ne peuvent donc pas être classifiées selon les critères retenus. Elles sont néanmoins prises en compte dans ce bilan en volume. Globalement, sur l’ensemble des RUPs, un peu plus d’un tiers (35%) des débarquements français proviennent d’espèces estimées en bon état, pour 21% provenant d’espèces surpêchées et/ou dégradées. Les espèces non évaluées représentent 43% des débarquements totaux. De fortes disparités existent entre les régions