Variability in frontal zone formation and distribution of gadoid fish larvae at the shelf break in the northeastern North Sea

Hydrography and larval fish distribution in the northeastern North Sea were studied during a research programme carried out during the period from 1991 to 1994. The aim was to examine the connection between frontal zone formation and nursery characteristics of gadoid larvae at the shelf break. Emphasis was placed on the year-to-year variation in frontal characteristics and distributional patterns of larvae An area of about 67000 km2 covering the northeastern North Sea, the Skagerrak and the Kattegat was surveyed by grid or transect sampling. At each sampling station the hydrography was studied by CTD casts, and the abundance of fish larvae was measured by depth integrating tows of a 2 m ring net. Five species of gadoid larvae and small luveniles were found in the area. cod Gadus rnorhua, whiting Merlangjus merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarki and saithe Pollachius virens. Larval abundance differed markedly between species and years. The abundance of all species was the highest in 1992 and declined during the follo~ving2 years. In 1994, cod and whiting were the only gadoid species observed. Peak abundance of all gadoids was found in the vicinity of the frontal zone; however, the relationship between larval distribution and hydrography differed among species. Correspondence between spatial and interannual variation in characteristics of frontal zones and larval distributions suggests that frontal zone variability is a central element in the early hfe of gadoid larvae from the area

Climatic changes in the deep Norwegian coastal waters and Skagerrak 2000-2005 in relation to previous decades

Poste

Temporal and spatial hydrographic variability in the Skagerrak

This report addresses the tempora1 and spatial variability in the hydrography of the Skagerrak by means of statistical investigations including frequency analyses and spatial correlations. The analysis is based on the fixed hydrographic section across the Skagerrak between Torungen (Arendal), Norway and Hirtshals, Denmark, close to a full year of temporally highly resolved hydrographic measurements by moored automatic current meters, placed off the coast from Torungen, and modelled output from the coupled physical-chemical-biological model system NORWECOM. NORSK SAMMENDRAG: Rapporten omhandler variabilitet i hydrografien i Skagerrak. Ved hjelp av statistiske metoder analyseres variasjonsmønstre i rom og tid. Metodene brukt omfatter frekvensanalyse og romlig korrelasjonsanalyse. Analysen tar utgangspunkt i det faste hydrografiske snittet som går på tvers av Skagerrak fra Torungen (Arendal) til Hirtshals, nær et år med tidsmessig godt oppløste strømmålinger fra en fast montert automatisk strømmåler plassert utenfor Torungen og modellresultater fra den fysisk-kjemisk-biologiske modellen NORWECOM

Hydrografiske undersøkelser og kartlegging av fiskefordeling i Nordsjøen i februar 1972

The present report outlines the results of a survey carried out by R. V. "G. O. Sars" and R. V. "Johan Hjort" in February 1972. The distribution and relative abundance of fish in the North Sea were mapped on the basis of echo integrator readings. Samples obtained by mid water and bottom trawls supported the identification of echo recordings and provided material for biological analyses of dominating fish species. The general features of the hydrography was determined, and the distribution of air and sea temperatures, temperature anomalies, and salinities are presented. Significant differences in echo integrator readings were observed: between day and night, between the two ships and in relation to obtained catch. Bottom trawl catches varied between 45 and 1545 kg per hour. Best catches were taken in the southeastern part of the North Sea. In total, herring, whiting and haddock amounted to 26, 25 and 21 per sent respectively while Norway pout, flatfish and other species each were less than 10 per cent in weight. Distribution, size, age etc. are reported in detail for the dominating species, and the relationship between the distribution and the abiotic environment is discussed, Young herring were found in greatest concentrations in the Bløden area. Sprat were found in the coastal waters, characterized by relatively low salinity, while Norway pout were most numerous in Atlantic water in the northern part on the North Sea plateau. Blue whiting and coalfish were mainly observed along the western slope of the Norwegian trench below the core of the Atlantic water which penetrates into the North Sea

Fjordbassengene i ytre Oslofjord. Oksygenforbruk, organisk belastning og vannutskifting. (Fjord basins of the Ytre Oslofjord, oxygen consumption, organic load and water exchange)

The major yearly inflow to the Ytre Osloford basins normally occure in the period March - July. In 1995 a stagnation period lastedfrom June until NovemberiDecember and an inflow periodfrom December to May 1996. The mean oxygen consumption rate for the Rauøy-Breidangen and Drøbak basin in the stagnation period were 0.14, 0.15 and 0.16 repectively. n e calculatedflux of particulate organic carbon to the Rauøy basin (6.5 g C m-2 month-l) was about twofold the flux of particulate organic carbon into the Breidangen and Dr~bakb asins (3.1 g Cm-2 month-l). Due to the deep sill leve1 (100-120 meter), and to intensive water exchange above it, the oxygen consumption (and the mean flux of particulate organic carbon) in the basins were most likely related to the in.ow of particulate organic matter from the Skagerrak coast. The main source of organic matter at the 100-120 m leve1 is probably injlowing water from the central and southern North Sea. Observations and calculations show that the mean oxygen minimum concentration in the Rauøy-Breidangen and Drøbak basins were approximately 4.7, 4.1 and 4.0 ml 1-1 respectively. Due to a general 50% increase in the oxygen consumption in sill basins along the Norwegian Skagerrak coast, the lowest mean oxygen concentrations have most likely been reduced by 0.5 ml 1-1 since around 1980. Ifthe mean oxygen consumption (and the mean flux of particulate organic carbon) in the Rauøy basin is increased by a factor of 2.-2.4, and in the Breidangen and Drøbak basin by a factor of 1.5-1.8, the oxygen concentration at the end of a stagnation period will most probably reach the critical oxygen limit of 3.0 ml 1-1. NORSK SAMMENDRAG:Det er vanlig med en årlig hovedinnstrømning av vann fra Skagerrakkysten til terskelbassengene i Ytre Oslofjord i perioden fra mars til juli. Innstrømningen har som oftest en varighet på ca 3 måneder, men kan variere mellom 1 og 6 måneder. Dette betyr at den årlige stagnasjonsperiode i bassengene normalt er ca 9 måneder, og kan variere mellom 6 og 11 måneder. I 1995196 var det en stagnasjonsperiode i de tre terskelbassengene på ca 6 måneder, fra juniljuli til novemberldesember 1995 og en innstrømningsperiode fra novemberldesember til mai 1996. De relativt høye bassengtetthetene våren 1996 vil bidra til å forlenge kommende stagnasjonsperiode i Ytre Oslofjord. I Rauøy - Breidangen - og Drøbakbassenget var midlere oksygenforbruk i stagnasjonsperioden tilnærmet likt, 0.14 - 0.16 ml 1-1 pr måned. Tilførslen av organisk materiale pr flateenhet var imidlertid omlag dobbelt så stor i Rauøybassenget (6.5 gC m-2 måned-1 ) som i Breidangen og Drøbakbassenget (3.0 - 3.1 gC m-2 måned-l). De tre bassengene i Ytre Oslofjord tilføres hovedsakelig organisk materiale fra kystvannet og den lavere organiske belastning i de to indre bassengene kan forklares ved den store avstanden fra kysten (60-80 km), dvs mye av det organiske materiale synker ut i Rauøybassenget før det når de indre terskelbasseng. Den relativt store vertikale transport av organisk materiale (6.0 - 6.5 gC m-2 måned-1 ) mellom 60 og ca 120 m dyp i kystområdet fra Ytre Oslofjord til Arendal skyldes trolig tilførsler av organisk materiale fra sjøområder utenfor Skagerrak og hovedkilden til den økte organiske belastning i disse dyp synes hovedsakelig å være innstrømmende vann fra sentrale og sørlige Nordsjø. Dagens midlere oksygenminimum i Rauøy, Beidangen og Drøbakbassenget er beregnet til henholdsvis ca 4.7, ca 4.1 og ca 4.0 ml 1-1. Midlere oksygenminimum i de tre bassengene er trolig redusert med ca 0.5 ml 1-1 som følge av en generell ca 50% Økning i den organiske belastning i kystvannet langs Skagerrakkysten etter ca 1980. Rauøybassenget har god kapasitet rnhp økt organisk belasting og dagens midlere oksygenforbruk og tilforsel av organisk materiale pr flatenhet i terskelnivå må økes 2.0-2.4 ganger før midlere oksygenkonsentrasjon i slutten av en stagnasjonsperiode kommer under den kritiske grense på 3.0 ml 1-1. I Breidangen og Drøbakbassenget er kapasiteten mindre og tilførslene av organisk materiale pr flateenhet kan bare Økes 1.5-1.8 ganger fØr oksygenkonsentras~onene å slutten av en stagnasjonsperiode blir mindre gode. Den totale omsetning av oksygen og organisk materiale i Rauøybassenget er også ca ti ganger stØrre enn i Breidangen og Drøbakbassenget. Regelmessige langtisdmålinger mangler i Ytre Oslofjord og det er derfor ønskelig at slike målinger iverksettes både for med større saerhet å kunne bestemme "normalsituasjonen" og variasjoner fra &r til år

Miljøundersøkelser i norske fjorder: Ytre Oslofjord 1937-2011

In the surface layer in Outer Oslofjord autumn temperatures were 2 - 4 °C above normal between 1996 and 2011 and summer temperatures (august) in 1995, 1997, 2002, 2004 and 2006 (19-21°C) were unormal high (19-21°C). In contrast summer temperatures in 2002 and 2003 were unormal low. In the basin water (300 m), influenced by Atlantic water, temperature increased with about 0.8°C after 1990 in accordance with the general temperature increase in Atlantic water along the Norwegian coast. About 0.5°C of the temperture increase seems to be connected to global warming and 0.3 °C to natural variations. The local input of antrohropogenic nutrients increased winter values of nitrate and summer values of chlorophyll - a in the upper layer of the Outer Oslofjord. The environmental conditions related to nitrate and chlorophyll-a were” less good” in the inner part of the fjord and “good” in the central part and in the coastal water. The oxygen conditions in the main basins in Outer Oslofjord, dominated by conditions in inflowing Atlantic water, were “very good”

Genome architecture enables local adaptation of Atlantic cod despite high connectivity

Adaptation to local conditions is a fundamental process in evolution; however, mechanisms maintaining local adaptation despite high gene flow are still poorly understood. Marine ecosystems provide a wide array of diverse habitats that frequently promote ecological adaptation even in species characterized by strong levels of gene flow. As one example, populations of the marine fish Atlantic cod (Gadus morhua) are highly connected due to immense dispersal capabilities but nevertheless show local adaptation in several key traits. By combining population genomic analyses based on 12K single nucleotide polymorphisms with larval dispersal patterns inferred using a biophysical ocean model, we show that Atlantic cod individuals residing in sheltered estuarine habitats of Scandinavian fjords mainly belong to offshore oceanic populations with considerable connectivity between these diverse ecosystems. Nevertheless, we also find evidence for discrete fjord populations that are genetically differentiated from offshore populations, indicative of local adaptation, the degree of which appears to be influenced by connectivity. Analyses of the genomic architecture reveal a significant overrepresentation of a large ~5 Mb chromosomal rearrangement in fjord cod, previously proposed to comprise genes critical for the survival at low salinities. This suggests that despite considerable connectivity with offshore populations, local adaptation to fjord environments may be enabled by suppression of recombination in the rearranged region. Our study provides new insights into the potential of local adaptation in high gene flow species within fine geographical scales and highlights the importance of genome architecture in analyses of ecological adaptation