SEAwise report on historic and future spatial distribution of fished stocks

This SEAwise report assesses the distribution of fish species across European seas. To this end, an ICES workshop, WKFISHDISH2, was co-organised to reach out to the broader scientific community and acquire as much knowledge as possible on scientific surveys and species distribution models. A large amount of historical scientific survey data, stored in the DATRAS and MEDITS databases, served as basis for the development of guidelines on how to appropriately pre-process such data, analyse them with state-of-the-art species distribution models (SDMs), and define metrics on how to compare species distributions. Distribution maps were generated separately for the Mediterranean Sea and the Northeast Atlantic spanning the Baltic Sea, North Sea, Celtic Seas, Bay of Biscay and Iberian Coast.  In general, there was good agreement between the distributions generated by different models that were applied to four different reference species with different characteristics in terms of spatial distribution. Differences between models were mainly related to the configuration of spatiotemporal processes, and the extrapolation, mainly in areas with few observations, or where correlates extend to values outside the observed range.  Trends in species distribution were species specific. Some species have shifted in a northward direction, while the distribution of other species was static, or characterized by a southward trend. It is difficult to have a mechanistic understanding, e.g. migration due to climate change, local outbursts, and/or local depletion of fish stocks, of these changes based on survey data that does not allow tracking of individual fish. Potential climate related shifts were instead investigated by linking the survey data with oceanographic variables generated through coupled hydrodynamic-biochemical models. This allowed us to explore how species distributions may change under different scenarios of climate change.  More information about the SEAwise project can be found at www.seawiseproject.org</p

SEAwise Report on the key species and habitats impacted by fishing

The implementation of ecosystem-based fisheries management requires knowledge on the ecological impact of fishing activities on species and their habitats – those both targeted and not targeted by fisheries. To identify which ecological impacts are key and what is known about them, SEAwise consulted stakeholders through European Advisory Councils and conducted a systematic review of the scientific literature to map the available knowledge and evidence. Specific reference was given to the bycatch of Protected, Endangered and Threatened (PET) species, benthic habitats, food webs and biodiversity, and impact from fisheries-related litter and ghost nets.  At the stakeholder consultations, sharks and/or elasmobranchs, turtles, species interactions, and seals or marine mammals were identified as top ranked in at least three out of the five regions. Other terms identified by at least two Case Study regions were: seabirds, sensitive species, benthic habitats, litter, PET species, invasive species and species interactions.  Relevant data were extracted from 549 retained papers. The majority of studies were conducted in the Mediterranean Sea, whereas only few papers reported on fishing impacts in the Baltic Sea (see figure below). Bony fish (teleosts) and benthos were the most studied ecosystem components in all Case Study regions, whereas marine mammals and cartilaginous fish were often studied in relation to bycatch of PET species.  Out of the 549 papers, most of them were related to fishing impacts on food webs and biodiversity and benthic habitats, followed by bycatch of PET species and other fishing impact studies (not related to any task). Fewest studies were related to the impact of fisheries-related litter and ghost nets. Demersal trawls were by far the most studied gear in studies on commercial fishing impacts. For recreational fisheries, hooks and lines, in particular angling, was the most studied fishing activity.  Among the items identified by the stakeholders, marine mammals, seabirds and reptiles were all covered in at least 25 papers each, indicating that there is a considerable body of knowledge even though not all areas may have information for all species. Litter was the key item that was least frequently reported on in the literature, especially outside the Mediterranean, where scientific papers were rare. As a consequence, areas outside the Mediterranean may lack information for further analysis unless a dedicated effort is made in SEAwise to remedy this. The regional differences in topics identified by stakeholder scoping did not reflect the regional amount of papers available.  This report describes results of the SEAwise project. More information about the project can be found at https://seawiseproject.org/</p

SEAwise Report on improved predictive models of growth, production and stock quality.

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 (EBFM) in their fisheries and understanding how ecological drivers impact stock productivity through growth, condition and maturity is essential to this proces. In this SEAwise report, we present the predictive models of fish growth, condition and maturity obtained so far in each of the four regional case studies.The biological processes (fish growth, condition and maturity) were studied in terms of body size (weight-at-age, length-at-age), condition factor, otolith increments and size at first maturity. Underlying data were available at different levels, ranging from individual fish, to sampling haul or stock level. Accordingly, the methods employed varied across case studies to adapt to the specific features of the process under study and the available data.The methodology encompassed statistical models (linear models, generalised additive models, mixed models, Bayesian nested hierarchical models, changepoint models), otolith growth increment analyses and mechanistic models (DEB-IBM model coupled to the environment and mizer model). Some of these models were focused on detecting overall trends, including potential changepoints along the time series or identification of the main intrinsic factors. Other models explored the impact of ecological drivers such as temperature, salinity, food availability or density dependence.In the Baltic Sea, two regimes were identified in the weight-at-age time series of herring in the Gulf of Riga (1961-1988 and 1989-2020). During the first period the main driver of the individual annual growth of the fish was the abundance of the copepod L. macrurus macrurus, while the abundance of the adult stages of E. affinis affinis was the dominating explanatory variable affecting herring growth during the second period. Neither SSB nor summer temperature during the main feeding period were significant drivers of the individual growth in the two distinct ecosystem regimes.In the Mediterranean Sea, the analysis of the impact of the environmental variables on biological parameters like size at first maturity, condition factor and growth in South Adriatic Sea and North-West Ionian Sea showed some significant effects in relation to the different species/area. In most of the cases, the environmental driver was bottom temperature, although some relationships with bottom salinity and primary production were also found. The model outcomes suggested that temperatures prevailing in deeper waters were the most significant factor affecting gonad maturity of hakes, while those in the shallow zone had the main impact on the L50 of red mullets. Condition factor of hake and red mullet in the Eastern Ionian Sea were affected not only by temperature, but also by zooplankton abundance.In the North Sea, mediated length-based growth models, linear mixed models and state-space linear mixed models were applied to four gadoids, two flatfishes and one pelagic stock and their performances were assessed in terms of model fit and predictive capability. For the mediated length-based growth model approach, the best model differed across stocks, but density dependent mediation effects were significant for five out of the seven stocks. Regarding the linear mixed models, the two types of models and the different penalisation procedures led to different models across stocks. Among the additional ecological variables, surface temperature was the most frequently included in the final model, closely followed closely by SSB and to a lesser extent by NAO. Detailed otolith increment analysis was used in the development of multidecadal biochronologies of average annual growth of sole in the North Sea and in the Irish Sea. In the North Sea, the best extrinsic model of sole growth included sea bottom temperature, fishing mortality at age, and stock biomass at maturity stage, and their interactions with age and maturity stage, while in the Irish Sea, the best extrinsic model included sea bottom temperature and fishing mortality at maturity stage and its interaction with maturity stage. These results confirmed the expected positive effect of temperature on adult growth. However, in the North Sea, temperature showed unexpected negative effect on juvenile growth, which might be linked to changes in food availability and/or intraspecific competition and need to be further studied. The mizer model (package for size-spectrum ecological modelling) with environmental forcing was used to study whether warming in the North Sea is responsible for the failure of the cod stock. The simulated fish community response when recruitment and carrying capacity depended on surface temperature fitted better with the assessment data than when the environment was fixed. However, the qualitative differences remain, suggesting that temperature effects were not the main cause of the model-assessment disparity.In the Western Waters, the mediated length-based growth models developed for the North Sea case study were applied to 14 stocks in the Celtic Sea. The best model differed across stocks, but again SSB mediation was significant for most of the stocks. From visual inspection of the plots, however, it was noted that the raw data from certain stock objects showed a reduced growth compared to the model fits, requiring further analyses. The analysis on biological measurements of individuals collected at fish markets, observers at sea or during scientific cruises allowed to study temporal variations in body size and condition factor of benthic, pelagic and demersal species in the Celtic Sea and the Bay of Biscay. The linear models indicated a significant negative monotonic relationship of sizes at all ages for anchovy and pilchard, but variations in size at age were less clear and significant for benthic and demersal species. In contrast, the results of the body condition indices showed a moderate but significant decrease for all the studied 19 species over time. The in-depth analysis for anchovy in the Bay of Biscay based on research surveys confirmed the decline in the length and weight of anchovy in the Bay of Biscay and pointed to a decline in body condition toward slender body shapes. Detected associations between temperature and size became more apparent for adult age classes than for juveniles, whereas the association between anchovy size and the biomass of spawners was more important for juvenile than for adult age classes. Associations between anchovy size and chlorophyll-a concentration were in general weak. Finally, the DEB-IBM model coupled to the environment that is under development for the two main seabass stocks of the North East Atlantic will provide further insights on how growth, condition and maturation can affect the future dynamics and productivity of these stocks.Read more about the project at www.seawiseproject.org</p

SEAwise Report on consistency of existing targets and limits for indicators in an ecosystem context

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 (EBFM) in their fisheries. This SEAwise report investigates the consistency of existing targets and limits from the Common Fisheries Policy (CFP) and the Marine Strategy Framework Directive (MSFD). Trade-offs between different objectives (ecological, economic, social), targets and limits are highlighted. A wide range of model types (from bio-economic to full ecosystem models) has been applied to various case study areas across the North East Atlantic and Mediterranean. Although model predictions are by nature uncertain, this study provides important information on likely inconsistencies between existing targets and limits and trade-offs expected under ecosystem- based fisheries management (EBFM). The scenarios investigated include the current range of management applied in terms of the Maximum Sustainable Yield (MSY) concept (i.e. strict MSY approach vs. Pretty Good Yield (PGY) approach allowing sustainable deviations from single species FMSY point estimates). The landing obligation is a key aspect of current fisheries management and was fully considered, in particular for mixed demersal fisheries.Maintaining current fishing effort without further management measures was the least sustainable option in nearly all cases studies. This approach led to increased risk of stocks falling below critical biomass limits. Although the fishing effort adaptions needed is highly case specific, this indicates that further management measures are likely to be needed to ensure a sustainable exploitation of all stocks.Scenarios applying a strict MSY approach in combination with the landing obligation (i.e. FMSY as upper limit with fisheries ending when the first stock reaches FMSY) in most case studies led to the lowest fishing effort. This had positive effects on MSFD related indicators such as bycatch of Protected, Endangered and Threatened (PET) species, benthic impact and the Large Fish Indicator as well as global indicators such as CO2 emission or ecosystem-based indicators like catch per km2. However, this scenario often led to the lowest catches from mixed demersal fisheries due to strong choke effects because fleets had to stop when their first quota was exhausted. This reduces social indicators such as food security, employment and wages. In terms of economic performance, the gains and loses were highly case specific. Scenarios applying the Pretty Good Yield concept and allowing sustainable deviations from the FMSY point estimate when stocks are in a healthy state often outperformed the scenarios applying FMSY as strict upper limit. Such scenarios, applying a more flexible interpretation of the MSY concept, led to reduced fishing effort compared to the status quo effort, but relaxed choke situations in mixed demersal fisheries to some extent leading to higher gross profits and in some case studies also to higher catches. Hence, they may constitute a compromise between the need to attain social as well as ecological objectives. Whether the associated effort levels lead to conflicts with MSFD objectives must be analysed when more internationally agreed thresholds become available for e.g., bycatch of PET species or benthic impact.The majority of case studies exceeded suggested thresholds for the global ecosystem indicators catch per km2 or primary production even under scenarios with high effort reductions. This can be explained to some extent by the fact that these indices are mainly driven by pelagic and industrial fisheries not always part of the models applied. Nevertheless, it indicates potential conflicts with such more holistic ecosystem indicators in their current form.Additional trade-offs in terms of yield were identified within the food web if e.g., demersal piscivorous predators feed on small pelagic fish and both groups are fished. Further, in case studies where small-scale fisheries (SSF) play an important role (e.g., Eastern Ionian Sea) additional trade-offs became apparent as different scenarios led to different ratios between revenues from small scale fisheries and revenues from large-scale fisheries. This adds another level of complexity when such aspects need to be taken more into account in future fisheries management under EBFM.The modelling assumed current selectivities and catchabilities will be maintained in the future. Especially trade-offs arising from fleets having to stop fishing when their first quota is exhausted or when e.g., a threshold for bycatch of PET species is reached may be resolved by improving selectivities via technical measures (e.g., closed areas or innovative gears) in the future. Deliverable 6.8 in month 36 will test such scenarios. Furthermore, the list of indicators and their targets and limits will be updated based on research within and outside SEAwise. Predictive capability of models will be enhanced by incorporating improved biological and economic sub-models in relation to environmental change. Climate change scenarios will be run and new harvest control rules (HCRs), proposed by SEAwise, will be tested. Finally, consistent targets and limits will be proposed for implementing EBFM.</p