| 1. |
- Howell, Daniel, et al.
(författare)
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Report of the Working Group on Multispecies Assessment Methods (WGSAM), 10-14 October 2016, Reykjavik, Iceland
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Working Group on Multispecies Assessment Methods (WGSAM) met in Reykjavik, Iceland, 10–14 October 2016. In this tenth report of the pan-regional WGSAM, work focused on four (B, E, F, G) of the multi-annual ToRs.Based on their knowledge, participants provided an updated inventory of progress of multispecies models in ICES Ecoregions (ToR A), noting those regions where no information was available. Reporting on ToR A was scarce compared to previous years, partly because recent relevant work was reported against ToR E and G instead.A Key Run (ToR B) of the Baltic Sea Ecopath with Ecosim (NS-EwE) model was presented and reviewed in detail by 4 WGSAM experts, and approved by the group following implementation of changes agreed in plenary at the meeting and verified by the 4 experts in January. The Key Run is documented in a detail in Annex 3, with key outputs summarised in Section 3 and data files made available on the WGSAM webpage). WGSAM also conducted an informal review of the LeMans modelling framework for potential application in the Irish Sea, and recommended adjustments to the framework for further review. Because the LeMans framework is a within-model ensemble addressing parameter uncertainty, this review also related to ToR D.Multispecies model skill assessment (ToR C) and multi-model ensemble methods (ToR D) were not emphasized this year. However, plans were made to coordinate future work for ToR C, and one ToR D presentation reviewed the utility of a dynamic multimodel ensemble for making inferences about the real world. This method can infer results for individual components of aggregate groups; the ensemble model uses correlations in other ecosystem models to determine what the models that group species would have predicted for individual species. A proof of concept for the North Sea was presented.Ecosystem indicator analyses (ToR E) were presented from a wide range of ecosystems. A theoretical analysis comparing results from the Celtic and North Seas with 4 “idealized” fleets was presented to analyse the performance of selected indicators in a multispecies mixed fishery. Four indicators including the Large Fish Indicator (LFI) were examined, and shown to have mixed utility in measuring the impact of different fleet sectors, with the best indicator varying by ecosystem. A multivariate analysis of ecosystem responses to multiple drivers was conducted for four US ecosystems using gradient forest method to identify potential ecosystem thresholds. Other multivariate methods were reviewed that draw on the strengths of multiple indicators for the Northeast US shelf ecosystem. A food web based biodiversity indicator was presented with an application for the Baltic Sea. This could be extended to any ecosystem with an EwE or similar model. A community status indicator relating a species-area relationship to the LFI and mean trophic levels was presented for the Swedish west coast.Impacts of apex predators on fisheries (ToR F) were examined with one presentation and a group discussion planning further work. A multipecies production model was parameterized to simulate interactions between three fish guilds, fisheries, and one marine mammal guild, concluding that fish reference points and trajectories change with marine mammal interactions. Fishery management was also important to reduce vessel interactions with and ensure prey supply to marine mammals. 4 | ICES WGSAM REPORT 2016 Exploration of practical advice for fisheries management incorporating multispecies, mixed fishery, and environmental factors (ToR G) was evident across regions. Two approaches for incorporating species, fleet, environmental, and other interactions are in progress in the Northeast US. One presentation outlined the New England approach, and another outlined the Mid-Atlantic approach. In New England, a management strategy evaluation is in progress to evaluate harvest control rules that consider herring's role as forage in the ecosystem. The modelling framework and stakeholder workshops were discussed. In the Baltic, a Nash Equilibrium optimisation approach incorporating environmental factors was presented for the cod-herring-sprat fishery to attempt to identify a solution that would give good yield for all species simultaneously. In the North Sea a theoretical analysis using 4 “idealized” fleets was presented to analyse the potential implications of "Pretty Good Yield" ranges around MSY. The model examined the likelihood of the fishery being precautionary for the different species given the uncertainties involved, and concluded that the upper ends of MSY ranges would not guarantee precautionarity.
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| 2. |
- Howell, Daniel, et al.
(författare)
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Report of the Working Group on Multispecies Assessment Methods (WGSAM), 9–13 November 2015, Woods Hole, USA
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Three meetings were held between 2013 and 2015 (Stockholm, London and Woods Hole), with progress being made on all the Terms of Reference. WGSAM has been making significant contributions required to enable ICES to develop its capability to give advice on the ecosystem impacts of fishing and climate change. This is a priority area identified in the ICES strategic plan and is consistent with scientific needs to support implementation of the Common Fisheries Policy and Marine Strategy Framework Directive. This final report summarises the key progress made against each ToR. A particularly important area established during this period has been the discussions that have led to guidelines on quality assurance of ecosystem models in-tended for advice giving. WGSAM prepared a specific briefing on this issue and con-tinues to work on issues related to model review processes, model validation and developing methods for generating advice from multi-model ensembles. These are all important areas of work in the evolution toward giving integrated, ecosystem-based advice to ICES clients. We recommend that ICES supports continuation of WGSAM new ToRs and considers more specifically how to support WGSAM in developing advice relevant products.
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| 3. |
- Poos, Jan Jaap, et al.
(författare)
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Harvest-induced maturation evolution under different life-history trade-offs and harvesting regimes
- 2011
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 279:1, s. 102-112
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Tidskriftsartikel (refereegranskat)abstract
- The potential of harvesting to induce adaptive changes in exploited populations is now increasingly recognized. While early studies predicted that elevated mortalities among larger individuals select for reduced maturation size, recent theoretical studies have shown conditions under which other, more complex evolutionary responses to size-selective mortality are expected. These new predictions are based on the assumption that, owing to the trade-off between growth and reproduction, early maturation implies reduced growth. Here we extend these findings by analyzing a model of a harvested size-structured population in continuous time, and by systematically exploring maturation evolution under all three traditionally acknowledged costs of early maturation: reduced fecundity, reduced growth, and/or increased natural mortality. We further extend this analysis to the two main types of harvest selectivity, with an individual's chance of getting harvested depending on its size and/or maturity stage. Surprisingly, we find that harvesting mature individuals not only favors late maturation when the costs of early maturation are low, but promotes early maturation when the costs of early maturation are high. To our knowledge, this study therefore is the first to show that harvesting mature individuals can induce early maturation.
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