SEAwise Report on improved predictive models of natural mortality under different distributional scenarios and incorporating experimental results

• Main Authors: Stefan Neuenfeldt, Anna Rindorf, Janneke Ransijn, Sophie Smout, Simon Northridge, Bernhard Kühn, Marc Taylor, Alexander Kempf, Robert Thorpe, Michael Spence, Morten Vinther, Ole Henriksen, Mikaela Potier, Morgane Travers-Trolet, Paul Gatti, Nis Sand Jacobsen
• Format: Text
• Language: unknown
• Published: 2024
• Subjects: Conservation and biodiversity; Environmental assessment and monitoring; Environmental management; Food webs; Indicators; Uncertainty; Marine ecosystems; Ecosystem Based Fisheries Management; Harbour porpoise
• Online Access: https://doi.org/10.11583/dtu.26068735.v1; https://figshare.com/articles/online_resource/SEAwise_Report_on_improved_predictive_models_of_natural_mortality_under_different_distributional_scenarios_and_incorporating_experimental_results/26068735

The SEAwise project works to deliver a fully operational tool that will allow fishers, managers, and policy makers to easily apply Ecosystem Based Fisheries Management. This SEAwise report describes natural mortality models for the North Sea, the Celtic Sea, Bay of Biscay and Western waters. The models differ in type and structure, and together reveal both temporal differences and structural uncertainties linked to the assumptions made when building the model. SMS, the model applied for the North Sea, is a stock assessment model including biological interaction estimated from a parameterised size-dependent food selection function. The model is formulated and fitted to observations of total catches, survey data and stomach contents for the North Sea. The predator and prey stocks available include as predators and prey (cod, whiting, haddock), prey only (herring, sprat, northern and southern sandeel, Norway pout), predator only (saithe, mackerel), no predator–prey interactions (sole and plaice) and ‘external predators’ (eight species of seabirds, starry ray, grey gurnard, North Sea horse-mackerel, western horse-mackerel, hake, grey seals and harbour porpoise). With respect to methodology, fish diets were recompiled with the R-package FishStomachs (with similar results as in the 2020 key run). These estimated uncertainties are now used as input to SMS, where such uncertainties were previously estimated within SMS. The predictive ability of multispecies models was only sometimes enhanced compared to single species assessments. However, the choice of whether to use variable or constant natural mortality greatly impacted the estimated stock recruitment relationship and reference points for stock biomass based on this. Measures of the variability in the estimated natural mortality between years was estimated to provide guidance for Management strategy evaluations in single species environments. The estimation was compared between different areas for the same species, providing a general guidance on the likely level of ...