Search

A minimum stoichiometric carbon and nitrogen model of an entire ecosystem based on Dynamic Energy Budget (DEB) theory is presented. The ecosystem contains nutrients, producers, consumers, decomposers and detritus. All three living groups consist of somatic structure and either one (consumers and decomposers) or two (producers) reserve compartments, hence the living matter is described by seven state variables. Four types of detritus are distinguished. As the system is closed for matter, the dynamics of the nutrients carbon dioxide and ammonium follow automatically from the dynamics of the other 11 state variables. All DEB organisms in the model are V1-morphs, which means that surface area of each organism is proportional to volume. The resulting ontogenetic symmetry implies that complicated modelling of size structure is not required. The DEB V1-morph model is explained in detail, and the same holds for the idea of synthesizing units, which plays a key role in DEB modelling. First results of system dynamics are presented.

The Workshop on pathways to climate-aware advice (WKCLIMAD) met in the autumn of 2021 to develop a proposal for an advisory framework that accounts for the influences of climate change on aquaculture, fisheries, and ecosystems. The workshop worked through online sessions with over 40 participants.Climate-informed advice should be provided through a risk-based framework that considers magnitude and likelihood of impacts, effectiveness and feasibility of measures. A wealth of data, tools and methods exists to on-ramp the advice. However, it is important to consider how these are utilised. To provide robust climate-informed advice, there is a need to identify and rank climate impacts and the associated risks, and match adaptation measures with public policy objectives. There must be a balance between actionable advice and reporting of uncertainty.The next steps for ICES should be to evaluate these three recommended additions to the advice framework/principles:• Development of a framework for spatial knowledge and advice, that includes definitions of temporal and spatial scale of management challenges.• Proactive solicitation of experts and stakeholders in relevant fields. Co-production of knowledge with iterative feedback, accounting for the plurality of knowledge and participation mechanisms.• Formulation of a plan for outputs, and communication, from the start of process, including allocation of sufficient resources to deliver advice.Greater emphasis needs to be placed on the communication and co-creation of advice.Climate-informed advice should include an assessment of current conditions in relation to the desired state. This requires not just an evaluation of the current state of the system, but the likely and/or desired future state of the fisheries/aquaculture system. This will also require greater effort on scoping of future scenarios of ecosystem state, and potential management measures for adaptation, and some mitigation. Advice should document the expected effects of specific management actions, giving attention to the potential distribution of management costs and benefits. Advice should be produced in response to requests but also be proactively produced by ICES. WKCLIMAD provides ICES with definitions, language and terminology that align with, and build on, those of the IPCC and calls on ICES to consistently use this terminology. The workshop also provides example lists of drivers, impacts, measures and potential actions.ICES needs to attract expertise from beyond its traditional areas of ecosystem and population dynamics and oceanography. Engagement with the plurality of the knowledge base is required, as a mean to refine goals, explore trade-offs between management objectives, as well as to build a common understanding and build knowledge about the system and efficient pathways of action to governance. WKCLIMAD considered that to provide credible climate-informed advice, the evidence base needs to be strengthened in the following scientific fields:• future scenarios of management options and ecosystem state• risk, vulnerability and resilience analysis of species, ecosystems, and human communities• spatial planning information and models• trade-offs among potential actions, and incentives for best practice sharing including technological developments• carbon accounting across the system• monitoring and early-warning systems

East Africa's Lake Victoria provides resources and services to millions of people on the lake's shores and abroad. In particular, the lake's fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria's system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake's social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks' vulnerability to exploitation but reduce society's vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.