Exploring the effects of discarding using the Atlantis ecosystem model for Icelandic waters

Publisher's version (útgefin grein)Discarding fish has been a part of the fisheries for centuries but it has been very difficult to monitor how much is discarded, especially in areas where it is an illegal activity. In this study the ecological and economic effects of discarding were investigated using the Atlantis model for Icelandic waters. Five different scenarios were compared, using different discarding rates and selectivities. The results showed that a complete stop of discarding fish (cod and haddock) and landing everything instead had little ecological and economic impact. Improved selectivity, which would result in not catching the fish that would be discarded, had great beneficial economic effects. The increase in biomass led to higher landings, which consequently led to higher revenue. Also, the cost decreased with increasing biomass, which increased the profit of the fisheries. None of the five scenarios had great ecological effects but only discarding of cod and haddock, which have low discard rates, were considered in this study.This study received funding from the European Commission’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 634495 for the Science, Technology, and Society Initiative to Minimize Unwanted Catches in European Fisheries (MINOUW).Peer Reviewe

End-to-end model of Icelandic waters using the Atlantis framework: Exploring system dynamics and model reliability

Publisher's version (útgefin grein)Icelandic waters are very productive and the fisheries are economically important for the Icelandic nation. The importance of the fisheries has led to progressive fisheries management and extensive monitoring of the ecosystem. However, fisheries management is mainly built on single species stock assessment models, and multi-species or ecological models are essential for building capacity around ecosystem-based fisheries management. This paper describes the first end-to-end model for the Icelandic waters using the Atlantis modeling framework. The modeled area is 1,600,000 km2, and covers the area from Greenland through Icelandic waters to the Faroe Islands. The ocean area was divided into 51 spatial boxes, each with multiple vertical layers. There were 52 functional groups in the model: 20 fish groups (8 at a species level), 5 groups of mammals, 1 seabird group, 16 invertebrates, 5 primary producers, 2 bacteria and 3 detritus groups. The reliability of the model was evaluated using a skill assessment and a sensitivity analysis was conducted to understand the dynamics of the system. The sensitivity study revealed that saithe, redfish and tooth whales had the greatest effect on other groups in the system. The skill assessment showed that the model was able to replicate time-series of biomass and landings for the most important commercial groups and that modeling of the recruitment processes was important for some of the groups. This model now provides a solid basis for evaluating alternative ecosystem and fisheries management scenarios, and should produce reliable results for the most important commercial groups.This study has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 613571 for the project MareFrame and from the European Commission’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 634495 for the project Science, Technology, and Society Initiative to minimize Unwanted Catches in European Fisheries (Minouw). Funding from the Icelandic Research Fund (rannis, No. 152039051) is also acknowledged.Peer Reviewe

Comparing the steady state results of a range of multispecies models between and across geographical areas by the use of the jacobian matrix of yield on fishing mortality rate

Like other fisheries models, multispecies models are subject to various sources of error. However, with regard to their use for ecosystem-based fisheries management (EBFM) between model errors are likely to be most important. As multispecies models are by definition many-dimensional, comparing them is potentially a complex task. The paper uses a simple approach. This is to calculate the Jacobian matrix of long term steady state catch by species with respect to the fishing mortality relative to status quo levels on all species. This enables the comparison of the relative strength of species interactions among models both within and between regions. This Jacobian matrix approach to comparing multispecies models is applied to available models for the North Sea, the Baltic Sea and from Icelandic waters. Moreover, this information is used to provide the basis for estimating a multidimensional quadratic yield surface for each model in the near field. Used this way it is possible to compare different model estimations of fishing mortality rate changes needed to approach yield-related management goals. The results suggest considerable variation between models in their detailed results but more coherence in suggesting directions for changing fishing mortality rate. Thus the approach is of considerable importance in specifying the confidence with which it is possible to make multispecies predictions for EBFM

Ecosystem Models of Lake Victoria (East Africa): Can Ecopath with Ecosim and Atlantis Predict Similar Policy Outcomes?

Ecosystem simulation models are valuable quantitative decision tools for supporting ecosystem-based fisheries management. However, the application of ecosystem models in fisheries management is still undermined by the lack of simple procedures to test the effect of model uncertainty on policy outcomes. The use of multiple ecosystem models is viewed as “insurance” against the effects of uncertainty emanating from modelling complex systems, which calls for investigations to ascertain whether models with different structure and assumptions can give consistent policy evaluations. We compared two structurally-distinct ecosystem models, Ecopath with Ecosim (EwE) and Atlantis, for Lake Victoria by varying fishing mortality of the key functional groups: Nile perch (the top predator) and haplochromines (key prey species). We compared model behaviour at the ecosystem level and at the level of functional groups, by evaluating changes in biomass of targeted groups and the consequent effects of changes in target groups on non-target groups. Results showed qualitative similarities (direction of change) for the major harvested groups; however, the cascading effects on non-target species varied across models, depending on the species interaction feedbacks. We conclude that: EwE and Atlantis, despite the huge differences in ecological processes between the models, can give consistent qualitative advice, which is needed for strategic management decisions; consistency in the representation of trophic interactions may help to minimize variations in simulated fishery responses due to model structure. This study helps to highlight scenarios that are robust to model choice, and for which simpler models (such as EwE) could also provide reliable advice