Botnfiskundersøkingar i Barentshavet vinteren 2000 : detaljert rapport

A combined acoustic and bottom trawl survey to obtain indices of abundance and estimates of length and weight at age has been carried out each winter (4-6 weeks in January-March) since 1981 in the Barents Sea. The target species are cod and haddock, but in recent years abundance indices have also been worked out for the redfish species and Greenland halibut. Since 1993 the survey area has been extended to the north and east in order to obtain a more complete coverage of the younger age groups of cod. In winter 1997 only the Norwegian part of the Barents Sea and a small part of the Svalbard area was covered, while in 1998 also a small part of the Russian EEZ was covered. In 1999 and 2000 the vessels had full access to the Russian EEZ

Workshop on hydro-acoustics scrutinizing in the Norwegian Sea

This report presents the international redfish survey carried out in the Norwegian Sea in August 2008 and the methodology used to review and compare the different hydroacoustic scrutinizing procedures. The results of the comparative analysis clearly show that differences in scrutinizing methods have a very large impact on the abundance estimate of redfish. They probably constitute the major source of uncertainty for any quantitative estimate. Efforts towards standardisation of scrutinizing procedures should be amplified or at least maintained

Geographic extent of introgression in Sebastes mentella and its effect on genetic population structure

publishedVersio

Three-dimensional post-glacial expansion and diversification of an exploited oceanic fish

Vertical divergence in marine organisms is being increasingly documented, yet much remains to be carried out to understand the role of depth in the context of phylogeographic reconstruction and the identification of management units. An ideal study system to address this issue is the beaked redfish, Sebastes mentella – one of four species of ‘redfish’ occurring in the North Atlantic – which is known for a widely distributed ‘shallow‐pelagic’ oceanic type inhabiting waters between 250 and 550 m, and a more localized ‘deep‐pelagic’ population dwelling between 550 and 800 m, in the oceanic habitat of the Irminger Sea. Here, we investigate the extent of population structure in relation to both depth and geographic spread of oceanic beaked redfish throughout most of its distribution range. By sequencing the mitochondrial control region of 261 redfish collected over a decadal interval, and combining 160 rhodopsin coding nuclear sequences and previously genotyped microsatellite data, we map the existence of two strongly divergent evolutionary lineages with significantly different distribution patterns and historical demography, and whose genetic variance is mostly explained by depth. Combined genetic data, analysed via independent approaches, are consistent with a Late Pleistocene lineage split, where segregation by depth probably resulted from the interplay of climatic and oceanographic processes with life history and behavioural traits. The ongoing process of diversification in North Atlantic S. mentella may serve as an ‘hourglass’ to understand speciation and adaptive radiation in Sebastes and in other marine taxa distributed across a depth gradient

Cod in the Barents Sea (Northeast Arctic cod): a review of the biology and history of the fishery and its management

This paper briefly reviews our knowledge of the spatial distribution, ecology, stocks dynamics and fishery for Northeast Arctic cod. The history of stock assessments and scientific advice, and of fisheries regulations and management strategies, are described and discussed

Spatial migration pattern of deep-sea redfish (Sebastes mentella Travin) in the Barents Sea as inferred from long-term research survey series [presentation]

Long term bilateral Russian/Norwegian scientific co-operation as a basis for sustainable management of living marine resources in the Barents Sea. Proceeding of the 12th Norwegian/Russian Symposium Tromsø, 21-22 August 2007Extended abstract (Full article included in special issue of Marine Biology Research (vol. 4, 2008), celebrating the 50 years of Norwegian-Russian research cooperation

Spatial migration pattern of deep-sea redfish (Sebastes mentella Travin) of the Norwegian-Barents population from survey data

Study of redfish migration by traditional tagging-methods faces great difficulties. The redfish taken onboard a vessel usually prove to be nonviable. A sharp hydrostatic pressure differential is lethal for the redfish having a closed swim bladder. The main purpose of the present paper is to determine migration pattern of the deep-sea redfish juveniles. To study the deep-sea redfish migration, data from annual Russian and Norwegian scientific trawl surveys conducted during autumn and winter of 1982-1995 were used. The Petersen method was applied to analyse size composition of the deep-sea redfish catches taken during the above trawl surveys. The conclusion made from prior researches that the deepsea redfish year classes of 1982 and 1988 were strong compared to their neighboring ones was confirmed. On the assumption that "peaks" in the length distributions of survey catches displayed strong yearclasses, the annual corresponding lengths were defined for the 1982 and 1988 year classes of deep-sea redfish at different age (from 0 to 7 years). Subsequently, using the database from trawl surveys and knowing the length of the deep-sea redfish from strong yearclasses at different age, the distribution of these yearclasses by year was mapped. Based on the analysis of these maps, migration patterns of the deep-sea redfish juveniles in the Barents and Norwegian Seas were plotted

Investigations on demersal fish in the Barents Sea winter 2002 : detailed report

A combined acoustic and bottom trawl survey to obtain indices of abundance and estimates of length and weight at age has been carried out each winter (4-6 weeks in January- March) since 1981 in the Barents Sea. The target species are cod and haddock, but in recent years abundance indices have also been worked out for the redfish species and Greenland halibut. Since 1993 the survey area has been extended to the north and east in order to obtain a more complete coverage of the younger age groups of cod. In winter 1997 only the Norwegian part of the Barents Sea and a small part of the Svalbard area was covered, while in 1998 also a small part of the Russian EEZ was covered. In 1999 and 2000 the Norwegian vessels had full access to the Russian EEZ, In 2001 and 2002 a Russian research vessel covered most of the areas where the Norwegian vessels did not have access, and a sufficient coverage was obtained. The main results in 2002 were: - the 2001 year class of cod is very weak and the 2000 year class is indicated to be somewhat below average. The 1999 and 1998 year classes is slightly higher than expected from last years survey; - the abundance indices of 5-8 year old cod (1997-1994 year classes) are as expected from the last years survey; - the numbers of 9 year and older cod are very low; - lengths and weights at age and weight increments are similar to those observed in 2001, while some increase was observed from 2000 to 2001; - the mortality rate has been reduced compared with the previous years for age group 6 and younger, while it has remained high for older age groups; - for haddock all the year classes 1998, 1999, 2000 and 2001 are indicated to be at or above average. The 1996 year class is below average, but considerably larger than the year classes 1992-1995, which are very weak; - length and weight at age and weight increment seem to have stabilized, after a period of increase over the years 1998-2000; - the abundance indices of the redfish species are among the lowest in the time series and there are no signs of unproved recruitment; - compared to the 2001-results the abundance indices of Greenland halibut in the size range 15 to 44 cm have decreased, while they have increased for the other size groups