International Council for the Exploration of the Sea
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Report of the Working Group on Integrated Ecosystem Assessments for the Norwegian Sea (WGINOR)

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posted on 2019-04-15, 00:00 authored by ICESICES
The final meeting of a 3-year term for Working Group on Integrated Ecosystem As-sessments for the Norwegian Sea (WGINOR) was held in Reykjavik, Iceland, on 26–30 November 2018 and was chaired by Per Arneberg (Norway) and Guðmundur J. Óskarsson (Iceland). The number of participants were 20, representing Norway (5+6 on correspondence), Iceland (6), the Faroes (2) and Canada (1).Progress on ToR A included updated assessment of the main components of the eco-system, a scoping process among stakeholders in Norway, development of methodol-ogy for integrated trend analyses and further development of the overall approach for IEA. New elements added for the latter are a system for ocean climate forecast, a food-web assessment, a framework for assessing warning signals with relevance for man-agement and repeated scoping among stakeholders. The state and development of the main components are as follows:• The Atlantic water mass in the Norwegian Sea was warmer and saltier over the period 2000–2016 than the long-term mean. However, during the last two years, 2017 and 2018, the temperature remained relatively warm while the salinity had a marked decrease. Two different mechanisms can explain this, increased fraction of subpolar water (fresh and cold) and low heat loss to the atmosphere in the Norwegian Atlantic flow. Under the assumption that cir-culation patterns do not change, this situation with anomalously fresh Atlan-tic water in the Norwegian Sea can be expected to continue and even increase in the coming years.• From high levels during the early 2000s, the zooplankton biomass index de-clined until 2010. Since then the index has increased and is currently around the long-term mean.• Norwegian spring-spawning herring Clupea harengus has not produced a strong year class after the productive period of 1998–2004, causing declining stock size since 2010. Individual growth rate has been relatively high in later years.• Stock size and summer feeding area of mackerel Scomber scombrus has in-creased the last decade, but estimated stock size declined from 2017 to 2018. There are indications of shifts in both spawning and nursery grounds. Indi-vidual growth varies and is related to mackerel density for all age groups.• Blue whiting Micromesistius poutassou biomass increased for several years af-ter 2011 but declined during the last year. Several strong year classes have been produced during the last years, but the 2016 and 2017 year classes are expected to be poor.• Since approximately 2013, Atlantic bluefin tuna Thunnus thynnus have re-turned to Norwegian waters and may have increased predation of pelagic fish.• The most strongly ice-associated seal species like harp, ringed and bearded seals are only found along the fringes of the Norwegian Sea, but they may nevertheless be affected by changes occurring in stocks like mackerel (Scomber scombrus), herring and blue whiting, which over the past decade have entered habitats that were previously Arctic.• Based on the most recent estimates, fin whales have the largest biomass of any marine mammals in the Norwegian Sea, followed by the much more abundant but smaller minke whales, and the few but large sperm and hump-back whales.


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