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Tórshavn, Faroe Islands

Jansen T.,Technical University of Denmark | Campbell A.,Marine Institute of Ireland | Kelly C.,Marine Institute of Ireland | Hatun H.,Faroe Marine Research Institute | And 2 more authors.
PLoS ONE | Year: 2012

It has been suggested that observed spatial variation in mackerel fisheries, extending over several hundreds of kilometers, is reflective of climate-driven changes in mackerel migration patterns. Previous studies have been unable to clearly demonstrate this link. In this paper we demonstrate correlation between temperature and mackerel migration/distribution as proxied by mackerel catch data from both scientific bottom trawl surveys and commercial fisheries. We show that mackerel aggregate and migrate distances of up to 500 km along the continental shelf edge from mid-November to early March. The path of this migration coincides with the location of the relatively warm shelf edge current and, as a consequence of this affinity, mackerel are guided towards the main spawning area in the south. Using a simulated time series of temperature of the shelf edge current we show that variations in the timing of the migration are significantly correlated to temperature fluctuations within the current. The proposed proxies for mackerel distribution were found to be significantly correlated. However, the correlations were weak and only significant during periods without substantial legislative or technical developments. Substantial caution should therefore be exercised when using such data as proxies for mackerel distribution. Our results include a new temperature record for the shelf edge current obtained by embedding the available hydrographic observations within a statistical model needed to understand the migration through large parts of the life of adult mackerel and for the management of this major international fishery. © 2012 Jansen et al. Source

Eigaard O.R.,Technical University of Denmark | Rihan D.,Bord Iascaigh Mhara | Graham N.,Marine Institute of Ireland | Sala A.,National Research Council Italy | Zachariassen K.,Faroe Marine Research Institute
Fisheries Research | Year: 2011

Based on information from an international inventory of gears currently deployed by trawlers in five European countries, the relationship between vessel engine power and trawl size is quantified for different trawl types, trawling techniques and target species. Using multiplicative modelling it is estimated that the fishing circle (or circumference) of trawls targeting shoaling species such as mackerel (Scomber scombrus) and herring (Clupea harengus) increases approximately 44.1. m with each 100. hp increase, whereas the increase for trawls targeting demersal species such as Nephrops (Nephrops norvegicus) and monkfish (Lophius piscatorius) is only approximately 9.4. m per 100. hp. Trawling technique also affects the relationship between vessel horsepower and fishing circle in that trawls used for pair trawling have a significantly (P< 0.001) lower rate of fishing circle increase with hp of a factor 0.56 of that of both twin and single trawls. Underlying these results is the definition of four geometrically different trawl typologies and corresponding target species, driven by the assumption that fishing mortality for a trawl gear is governed by its geometry and proportional to its size, as understood by existing knowledge of the interactions between trawl gear and target species. The modelling results have implications for the reliability of kilowatt days as descriptor of effective effort and point to the need of including metrics relating to the size and geometry of gear deployed in routine monitoring of fishing effort. © 2011 Elsevier B.V. Source

Libungan L.A.,University of Iceland | Oskarsson G.J.,Iceland Marine Research Institute | Slotte A.,Norwegian Institute of Marine Research | Jacobsen J.A.,Faroe Marine Research Institute | Palsson S.,University of Iceland
Journal of Fish Biology | Year: 2015

Otolith shape variation of seven Atlantic herring Clupea harengus populations from Canada, the Faroe Islands, Iceland, Ireland, Norway and Scotland, U.K., covering a large area of the species' distribution, was studied in order to see if otolith shape can be used to discriminate between populations. The otolith shape was obtained using quantitative shape analysis, transformed with Wavelet and analysed with multivariate methods. Significant differences were detected among the seven populations, which could be traced to three morphological structures in the otoliths. The differentiation in otolith shape between populations was not only correlated with their spawning time, indicating a strong environmental effect, but could also be due to differing life-history strategies. A model based on the shape differences discriminates with 94% accuracy between Icelandic summer spawners and Norwegian spring spawners, which are known to mix at feeding grounds. This study shows that otolith shape could become an accurate marker for C. harengus population discrimination. © 2015 The Fisheries Society of the British Isles. Source

Olafsdottir A.H.,Faroe Marine Research Institute | Slotte A.,Norwegian Institute of Marine Research | Jacobsen J.A.,Faroe Marine Research Institute | Oskarsson G.J.,Iceland Marine Research Institute | And 2 more authors.
ICES Journal of Marine Science | Year: 2016

Weight-at-length and length-/weight-at-age were analysed for mature 3- to 8-year-old Northeast Atlantic mackerel (Scomber scombrus; n= 26 084) collected annually in autumn (September and October) at the end of the annual feeding season during 1984-2013 in the northern North Sea. The age range represented 92% of the mackerel stock size (age 3+). During the most recent decade, mackerel length- and weight-at-age continually declined. In 2013, the average mackerel was 3.7 cm shorter and weighed 175 g less than the average individual in 2002. Individual weight-at-length, demonstrating annual summer feeding success, continually declined during the most recent 5 years, whereas somatic growth of cohorts aged 3-8 continually declined for the last 11 of 25 cohorts investigated. Growth of the latest cohort was 34% of the maximum cohort growth recorded. Both weight-at-length and cohort growth were negatively affected by mackerel stock size and Norwegian spring-spawning herring (Clupea harengus) stock size (weight-at-length: r2 = 0.89; growth (length): r2 = 0.68; growth (weight): r2 = 0.78), while temperature was not significant. Conspecific density-dependence was most likely mediated via intensified competition associated with greater mackerel density. Negative effects of herring were likely mediated by exploitative competition for shared food resources rather than direct competition due to limited spatio-temporal overlap between mackerel and herring during the feeding season. Herring begin their seasonal feeding migration at least a month before mackerel; therefore, herring consumption influences prey availability for the later-arriving mackerel. Record low mackerel growth and negative effects of mackerel and herring stock size suggest that the carrying capacity of the Norwegian Sea and adjacent areas for plankton-feeding fish stocks have been reached. However, compounding effects of a less productive Norwegian Sea during the 30-year period cannot be excluded. © 2015 International Council for the Exploration of the Sea. Source

Hansen B.,Faroe Marine Research Institute | Hatun H.,Faroe Marine Research Institute | Kristiansen R.,Faroe Marine Research Institute | Olsen S.M.,Danish Meteorological Institute | Osterhus S.,University of Bergen
Ocean Science | Year: 2010

The flow of Atlantic water across the Greenland-Scotland Ridge (Atlantic inflow) is critical for conditions in the Nordic Seas and Arctic Ocean by importing heat and salt. Here, we present a decade-long series of measurements from the Iceland-Faroe inflow branch (IF-inflow), which carries almost half the total Atlantic inflow. The observations show no significant trend in volume transport of Atlantic water, but temperature and salinity increased during the observational period. On shorter time scales, the observations show considerable variations but no statistically significant seasonal variation is observed and even weekly averaged transport values were consistently uni-directional from the Atlantic into the Nordic Seas. Combining transport time-series with sea level height from satellite altimetry and wind stress reveals that the force driving the IF-inflow across the topographic barrier of the Ridge is mainly generated by a pressure gradient that is due to a continuously maintained low sea level in the Southern Nordic Seas. This implies that the relative stability of the IF-inflow derives from the processes that lower the sea level by generating outflow from the Nordic Seas, especially the thermohaline processes that generate overflow. The IF-inflow is an important component of the system coupling the Arctic region to the North Atlantic through the thermohaline circulation, which has been predicted to weaken in the 21st century. Our observations show no indication of weakening. © Author(s) 2010. Source

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