Stefán Áki Ragnarsson

Stefán Áki Ragnarsson
Marine and Freshwater Research Institute | MRI

PhD

About

65
Publications
14,620
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
983
Citations
Introduction
Skills and Expertise

Publications

Publications (65)
Article
Full-text available
During RV MS Merian expedition MSM75, an international, multidisciplinary team explored the Reykjanes Ridge from June to August 2018. The first area of study, Steinahóll (150–350 m depth), was chosen based on previous seismic data indicating hydrothermal activity. The sampling strategy included ship- and AUV-mounted multibeam surveys, Remotely Oper...
Presentation
Full-text available
Implementing European marine policies in the deep waters of the North Atlantic
Presentation
Full-text available
Towards the assessment of North Atlantic deep sea ecosystems’ status: opportunities and challenges unraveled by the ATLAS project.
Article
Full-text available
Divulgative paper published in Journal Eco Magazine, Deep Sea Issue
Article
Full-text available
The deep sea is the largest biome on Earth but the least explored. Our knowledge of it comes from scattered sources spanning different spatial and temporal scales. Implementation of marine policies like the European Union's Marine Strategy Framework Directive (MSFD) and support for Blue Growth in the deep sea are therefore hindered by lack of data....
Technical Report
Full-text available
The Marine and Freshwater Research Institute is studying and monitoring the effects of fish farming on the sediment in fjords. The aim is to understand these effects on sediment chemistry of areas that the fish farming companies are not obligated to monitor (far‐field areas) and also to establish base‐line knowledge about the sediments from areas t...
Technical Report
Full-text available
In a ‘bottom-up’ approach, WGECO compiled a list of candidate indicators for use in the ICES Ecosystem Overviews (EOs; ToR d.). These were mostly indicators which were scored earlier for their applicability for the EOs by WKFOOI, WKBIODIV and WGECO (including those in the 2018 WGECO report). A new scoring system for operationality was set up, based...
Article
Full-text available
The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodive...
Technical Report
Full-text available
The EU enacted new legislation on regulating access to deep-sea fisheries in 2016. Two important aspects of the regulation are outstanding, namely the establishment of a list of areas where vulnerable marine ecosystems (VMEs) are known to occur or are likely to occur and the determination of the existing deep-sea fishing areas, the so-called “fishi...
Technical Report
Full-text available
Presentation
Full-text available
Progress in Assessing Good Environmental Status in Deep-sea Benthic Ecosystems: D1, D3, D6 and D10.
Article
The association between fish assemblages and cold-water coral habitats was evaluated based on analysis of longline catches in the Lónsdjúp trough, SE-Iceland. In 2009 and 2010, longlines were set in locations with varying coral cover within the trough. The study site is characterised by a depression (50-100 m deep), intersected by several ridges. C...
Article
Full-text available
Knowing movement and structure of fish populations is a prerequisite for effective spatial fisheries management. The study evaluates migration patterns and connectivity of two groups of cod (Gadus morhua) associated with offshore feeding and nursery grounds. This was achieved by investigating (i) migration pathways of cod tagged at the feeding area...
Technical Report
Full-text available
Article
Changes in stock size of a top predator have been found to cascade through the trophic levels but the mechanism has not been fully clarified. Using data from annual trawl surveys within a fjord during 1988-2015, we present evidence that changes in abundance of cod Gadus morhua and haddock Melanogrammus aeglefinus have an immediate effect on the dis...
Technical Report
Full-text available
The 2016 meeting of WGECO was held at the ICES HQ in Copenhagen, Denmark from 6–13 April 2015. The meeting was attended by 17 delegates from 13 countries, and was chaired by Anna Rindorf (Denmark). The work conducted was centred on six Terms of Reference and two advisory requests concerning indicators of Good Environmental Status (GES) of the benth...
Chapter
Full-text available
Various human activities can have an impact on cold-water coral (CWC) habitats. Bottom trawling has been shown to degrade these habitats and, in some cases, to cause extensive damage. Among static fishing gears, bottom longlines and gillnets can be set directly on coral grounds. Intensive fishing with these gears, while having much less impacts com...
Article
Full-text available
The study analyses the home ranges and spatial segregation of spawning components of Icelandic cod Gadus morhua based on: (1) conventional tag (CT) recaptures and (2) depth, temperature and tidal locations from electronic data storage tags (DSTs). A total of 5987 CT recapture positions from tagging in geographically distinct spawning grounds from 1...
Article
Full-text available
The distribution of nine cold-water corals in the cold temperate North Atlantic is described based on existing records. The species studied are: Lophelia pertusa, Madrepora oculata, Paragorgia arborea, Primnoa resedaeformis, Paramuricea placomus, Acanella arbuscula, Isidella lofotensis, Radicipes gracilis, and Acanthogorgia armata. The compiled num...
Article
Full-text available
The effects of the habitat modification by the horse mussel Modiolus modiolus on the abundance and diversity of benthic fauna are poorly known. In this study we examined the effects of the abundance of M. modiolus, substrate properties, stone cover and spatial location on the abundance and species richness of the associated megafauna in Faxaflói Ba...
Article
The European Marine Strategy Framework Directive (MSFD) requires European states to maintain their marine waters in ‘Good Environmental Status’. The MSFD includes 11 descriptors of “Good Environmental Status” (GES), including “Sea-floor Integrity”. This descriptor is defined as: “Sea-floor integrity is at a level that ensures that the structure and...
Article
Full-text available
Rice, J., C. Arvanitidis, A. Borja, C. Frid, J. Hiddink, J. Krause, P. Lorance, S. A. Ragnarsson, M. Skold, B. Trabucco, 2010. Marine Strategy Framework Directive – Task Group 6 Report Seafloor integrity. EUR 24334 EN – Joint Research Centre, Luxembourg: Office for Official Publications of the European Communities: 73 pp.
Article
Full-text available
Schopka, S. A., Solmundsson, J., Ragnarsson, S. A., and Thorsteinsson, V. 2010. Using tagging experiments to evaluate the potential of closed areas in protecting migratory Atlantic cod (Gadus morhua). – ICES Journal of Marine Science, 67: 1024–1035. About 5200 cod (Gadus morhua) were tagged on three fishing grounds and within two marine protected a...
Article
Full-text available
Thorarinsdóttir, G. G., Jacobson, L., Ragnarsson, S. Á., Garcia, E. G., and Gunnarsson, K. 2010. Capture efficiency and size selectivity of hydraulic clam dredges used in fishing for ocean quahogs (Arctica islandica): simultaneous estimation in the SELECT model. – ICES Journal of Marine Science, 67: 345–354. Estimates of capture efficiency and size...
Article
Full-text available
The density and mean size of demersal fish were analysed inside and outside three protected areas off the northern coasts of Iceland. One-way ANCOVA and mixed effects models, with depth, bottom temperature and tow duration as covariates, were used to determine differences in the two metrics between areas. In general, these differences were not stat...
Article
Full-text available
A field experiment was conducted to examine the short- and long-term effects of otter trawling on a macrobenthic infaunal community in shallow subtidal waters of Faxafloi Bay (SW Iceland) that had never been trawled before. The experimental design consisted of 4 sites trawled 10 times and 4 areas left undisturbed (controls). Sampling of fauna and s...
Article
Stomach data were examined to assess the key factors that determine diet composition in some of the most important demersal fish species in Icelandic waters and to identify major feeding guilds. The data were collected during the groundfish surveys conducted by the Marine Research Institute in 1992. The factors examined included geographic position...
Article
Full-text available
The effect of reduced fishing effort on the demersal fish community, following area closures in 1993, was analysed for two protected areas off the east coast of Iceland, Digranesflak and Breiddalsgrunn. The data were collected using a standardized bottom trawl during groundfish surveys in the period 1985–2004. The aspects of the fish community that...
Article
Effects of scallop dredging on benthic communities in Breidafjordur, west Iceland, were investigated by analysing bycatch data from scallop stock assessment surveys and effort data from the commercial scallop fishery. Bycatch constituted 28% of the total catch, with eight benthic macrofaunal taxa alone making Lip nearly 98% of the bycatch. Modiolus...
Article
Full-text available
Over the last few decades, there is a growing understanding that harvesting natural resources can influence the structure and functioning of marine ecosystems. For that reason, there is an increased interest for an ecosystem-based approach to management. For an ecosystem-based management to be fully operational, it is important to identify those ke...
Article
We examined the spatial distribution of trawling effort from logbook data from all Icelandic vessels fishing for demersal fish between 1991 and 1997 with a spatial resolution of 1 degree of latitude and 1 degree of longitude. The trawling effort was widely distributed but was intensive only in small and localised areas. Three measures of effort wer...
Article
Full-text available
The seasonal pattern of bivalve spat settlement in Eyjafjordur, North Iceland, was investigated using artificial collectors of monofilament netting over 14 months (March 1998—January 2000) at 5, 10 and 15 m depth. SCUBA divers replaced the collectors at 4-weekly intervals. Twelve bivalve species settled on the collectors but only Mytilus edulis and...
Article
Full-text available
Abundance of ocean quahog (Arctica islandica) was estimated with underwater photography and a hydraulic dredge at 15 m depth in Önundarfjördur, NW Iceland. Abundance estimates based on counts of siphons from the underwater photographs were much higher than from analysis of the dredge catches. A total of seven taxa were identified from photographs,...
Article
Full-text available
In the present study three experiments were carried out out to measure the overall efficiency of a commercial hydraulic dredge used to surway ocean quahog in Icelandic waters. Direct effects of hydraulic dredging activity on ocean quahog populations by estimating size selectivity of the dredge and rate of shell breakage were evaluated. The mean dre...
Article
Full-text available
In many coastal areas fishing constitutes the dominant anthropogenic impact on coastal ecosystems. That fishing has altered the abundance and size spectra of fish communities is beyond doubt. We use time series of the abundance, in the North Sea, of 8 demersal fish species and data on food consumption rates to reconstruct a time series of benthic p...
Article
Two field experiments were carried out to investigate the effects of mussels (Mytilus edulis) on fauna and on sediment characteristics. In the first experiment mussels were removed from within an established mussel bed to create bare patches and in the second experiment mussels were transplanted to an adjacent bare sandflat. In the mussel removal e...
Technical Report
Full-text available
Thesis
Full-text available
Thesis (Ph. D.)--University of Aberdeen, 1996.
Conference Paper
Full-text available
The size of disturbed patches is thought to influence the rate of colonization. The hypothesis was tested on the Ythan Estuary, Scotland, by a field experiment where rates and modes of colonization of azoic patches of different size (1600 cm 2 versus 55 cm 2) were compared. None of the invertebrates recorded differed significantly in abundance betw...
Article
Full-text available
The management tools required for the practical application of an ecosystem-based approach to environmental management is still under development as a management tool. If such new management schemes are to be workable and effective it is imperative that they focus on the key processes rather than attempt to address the huge number of potential vari...

Network

Cited By

Projects

Projects (5)
Project
iAtlantic will assess the risks and vulnerabilities of deep- and open-ocean Atlantic ecosystems to climate change and other stressors to identify where and when improved management measures are most needed to maintain ocean health. Website: http://www.iatlantic.eu/ This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement no. 818123.This output reflects only the author's view and the European Union cannot be held responsible for any use that may be made of the information contained therein. Date: 1 June 2019 – 31 May 2023
Project
Mapping habitat forming species, vulnearable marine ecosystems and hydrothermal vent habitats on the Reykjane Ridge.