| 1. |
- Börjesson, Patrik, et al.
(författare)
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Spawning of Kattegat cod (Gadus morhua)—Mapping spatial distribution by egg surveys
- 2013
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 147, s. 63-71
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Tidskriftsartikel (refereegranskat)abstract
- The Kattegat cod has been heavily depleted and is classified as exhibiting reduced reproductive capacity. There is therefore a need for updated information on cod spawning activity and specific locations of spawning grounds in the area. To address this, data from dedicated egg surveys in the Kattegat between 2004 and 2006 were analysed. Positively identified cod eggs confirmed that cod were spawning in the area during the period. The estimated daily egg production was highest in the southeastern part of the surveyed area (~20 eggs m−2 d−1) close to the entrance of the Sound and off the Swedish coast. North of latitude 56°45′ N the daily egg production was low (0–5 eggs m−2 d−1). The predicted distribution of daily egg production was broadly consistent with the two major spawning areas proposed by Vitale et al. (2008), although shifted southwards emphasizing the importance of the southernmost spawning area closer to the Sound. These results provide a baseline for future studies of spawning and life history characteristics of Kattegat cod, and also in studies designed to disentangle the stock complex in the Kattegat-Sound-Belt area.
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| 2. |
- Hátún, Hjálmar, et al.
(författare)
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An inflated subpolar gyre blows life toward the northeastern Atlantic
- 2016
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Ingår i: Progress in Oceanography. - 0079-6611. ; 147, s. 49-66
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Tidskriftsartikel (refereegranskat)abstract
- Deep convection in the Labrador and Irminger Seas inflates the cold and low-saline subpolar gyre, which is a rich nutrient and zooplankton source for the surrounding warmer waters of subtropical origin. The zooplankton abundances on the south Iceland shelf show characteristic sub-decadal variability, which closely reflect the oceanic abundances of the ecologically most important zooplankton species – Calanus finmarchicus. Much higher abundances of this species are observed during years when the winter mixed layer depths (MLD) in the Labrador-Irminger Sea, and over the Reykjanes Ridge are deep. Furthermore, a tight relationship is identified between on-shelf zooplankton abundances and lateral shifts of the biologically productive subarctic front southwest of Iceland. Thus, we suggest that northeastward expansion of the subpolar gyre results in biologically productive periods in the waters southwest of Iceland – both oceanic and on the shelf. In addition to local atmospheric forcing, we find that the MLD and frontal position are also impacted by remote heat losses and convection in the Labrador Sea, through northward advection of unstable mode waters. The sub-decadal oceanic and on-shelf biological production peaks are possibly predictable by half a year (local winter convection to subsequent summer production), and the advective time-lag from the Labrador Sea might induce an even longer predictability horizon (up to 1.5 years).
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| 3. |
- Hátún, Hjálmar, et al.
(författare)
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Marine climate and mackerel distribution.
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- During fall 2012, the Polar research institutes in Russia (PINRO) and the Faroe marine research institute (FAMRI) continued the collaboration and the scientific work initiated in Tórshavn March 2006 on how the marine climate in the southern Nordic Seas might influence the spatial distribution of the mackerel stock in the Nordic Seas. Commercial catch data from the Russian fleet were analyzed together with a selection of comprehensive spatio-temporal oceanographic and biological observations. Pronounced sub-decadal variability is found both in the physical and the biological data, and the apparent synchronicity between these allows us to hypothesize three plausible mechanistic linkages. Much of the variability is ascribed to the spatially shifting Iceland-Faroe Front, and metrices for these fluctuations are presented. Our analysis should merely be regarded as ground work, upon which more detailed and finalized work could be conducted. We suggest continued Russian-Faroese collaboration, to further pursue these important questions.
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| 4. |
- Hátún, H., et al.
(författare)
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The dynamics of the North Atlantic subpolar gyre introduces predictability to the breeding success of kittiwakes
- 2017
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Since the open-ocean subpolar Atlantic is amongst the most predictable regions in the world, our results hold promise for predicting the general production to seabird populations over a large geographical region adjacent to the northern North Atlantic and the Arctic Mediterranean. Colonies of black-legged kittiwakes Rissa tridactyla in the North Atlantic have declined markedly since the mid-1990s, partly due to repeatedly failing breeding seasons. We show a close link between the breeding success of a kittiwake colony in the Faroe Islands and the subpolar gyre index. Successful breeding follows winters with an expanded subpolar gyre and, by inference, increased zooplankton abundances southwest of Iceland. The environmental conditions in the northwestern Atlantic during the non-breeding and pre-breeding seasons might therefore be important. Furthermore, the subpolar gyre dynamics might influence the local food abundance on the Faroe shelf during the breeding season. © 2017 Hátún, Olsen and Pacariz.
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| 5. |
- Hatun, H., et al.
(författare)
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The subpolar gyre regulates silicate concentrations in the North Atlantic
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The North Atlantic is characterized by diatom-dominated spring blooms that results in significant transfer of carbon to higher trophic levels and the deep ocean. These blooms are terminated by limiting silicate concentrations in summer. Numerous regional studies have demonstrated phytoplankton community shifts to lightly-silicified diatoms and non-silicifying plankton at the onset of silicate limitation. However, to understand basin-scale patterns in ecosystem and climate dynamics, nutrient inventories must be examined over sufficient temporal and spatial scales. Here we show, from a new comprehensive compilation of data from the subpolar Atlantic Ocean, clear evidence of a marked pre-bloom silicate decline of 1.5-2 mu M throughout the winter mixed layer during the last 25 years. This silicate decrease is primarily attributed to natural multi-decadal variability through decreased winter convection depths since the mid-1990s, a weakening and retraction of the subpolar gyre and an associated increased influence of nutrient-poor water of subtropical origin. Reduced Arctic silicate import and the projected hemispheric-scale climate change-induced weakening of vertical mixing may have acted to amplify the recent decline. These marked fluctuations in pre-bloom silicate inventories will likely have important consequences for the spatial and temporal extent of diatom blooms, thus impacting ecosystem productivity and ocean-atmosphere climate dynamics.
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| 6. |
- Pacariz, Selma, 1973, et al.
(författare)
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A model study of the large-scale transport of fish eggs in the Kattegat in relation to egg density
- 2014
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Ingår i: Ices Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 71:2, s. 345-355
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Tidskriftsartikel (refereegranskat)abstract
- A process-oriented model, with high vertical resolution, has been used to investigate variation in the transport of fish eggs and early larvae in relation to egg density. The main focus is on gadoid eggs from the spawning grounds in the southern Kattegat. Additionally, transport from the neighbouring areas, the central Kattegat and Oresund, is presented. The model results clearly indicate that transport is dependent on the egg density; lighter eggs are transported northwards whereas heavier eggs are to a larger extent retained or transported southwards. This study suggests that optimum densities in order to promote retention in the southern Kattegat are in the range of 1023-1026 kg m(-3). Observations from 2005 and 2006 of the vertical distribution of gadoid eggs combined with hydrographical data indicated high concentrations of eggs at the upper part of the pycnocline at densities of 1017-1022 kg m(-3). Combining the observations and modelling results on amount of dispersal and retention, suggests that gadoid eggs are mainly retained in the southern Kattegat (although shifted from maximum retention density) and simultaneously dispersed northwards. Even though the results of the study are described in the context of gadoid eggs, the results are applicable for other marine species with pelagic stages and buoyant particles within the tested density range.
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| 7. |
- Pacariz, Selma, 1973, et al.
(författare)
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Climate change and passive transport of European eel larvae
- 2014
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Ingår i: Ecology of Freshwater Fish. - : Wiley. - 0906-6691 .- 1600-0633. ; 23:1, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- One hypothesis to explain the large decline in the recruitment of the European eel (Anguilla anguilla) from the 1980s onwards is that a change in ocean circulation has influenced the drift of eel larvae, resulting in lower recruitment. To test this hypothesis, a simple Lagrangian model was constructed to simulate a passive drift from the spawning area in the Sargasso Sea to the European shelf. The simulation utilised the velocity data from a reanalysis of ocean climate, the Simple Ocean Data Assimilation (SODA 2.1.6), for the period 1958–2008 covering the time of regime shift in eel recruitment. The average drift time and latitudinal distribution of the arrival of eel larvae were explored for a range of constant depth levels and instantaneous mortalities. The model showed that the proportion of eel larvae carried by the North-East Atlantic Current to northern latitudes of arrival was greater before 1970, whereas there was an increase in amount of larvae being entrained into the southbound current branches after this time. The overall success of drift from the spawning area to the East Atlantic was not affected and clearly contradicts that this could explain the observed recruitment decline.
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| 8. |
- Pacariz, Selma, 1973, et al.
(författare)
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Interannual variability in the transport of fish eggs in the Kattegat and Öresund
- 2014
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 71:7, s. 1706-1716
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Tidskriftsartikel (refereegranskat)abstract
- The dispersal and retention of early life stages are essential factors for the recruitment of fish stocks, and often depend on local meteorological and hydrographical conditions. A BAltic sea Long-Term large Scale Eutrophication Model (BALTSEM) was used to examine interannual variation in the retention and dispersal of fish eggs, Atlantic cod (Gadus morhua) at spawning areas in the Kattegat andO¨ resund and to investigate the mechanisms responsible for this variation. Model simulations over period 1971–2006 showed that years with high retention were related to variableweak winds and a strong outflow of water from the Baltic Sea, while years with low retention were related to strong westerly winds. Low egg retention was associated with enhanced southward transport from the Kattegat towards the Great Belt and from theO¨ resund towards the Baltic Sea. This southward transport of eggs was highly correlated with the local westerly wind component. The southbound egg transport and the westerly wind Component both increased after 1989, and were connected with a change in the large-scale atmospheric circulation pattern, as represented by the NAO index. Results of this study provide information about the connectivity between neighboring areas and suggest that sedimentation is an important mortality factor.
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| 9. |
- Pacariz, Selma, 1973
(författare)
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MODEL STUDIES OF FISH EGG AND LARVAL TRANSPORT IN THE KATTEGAT AND THE NORTH ATLANTIC
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For the early life stages of fish, the dispersal and retention are important factors regarding present and future survivorship, growth and reproduction. The main objective of this thesis is to analyse fish egg and larval transport in two different marine systems, the Kattegat and the North Atlantic. The focus is on two different species, namely Atlantic cod (Gadus morhua) eggs in the Kattegat-Öresund-Belt area and European eel (Anguilla anguilla) leptocephalus larvae in the North Atlantic. The stock of cod in the Kattegat has been severely depleted due to fishery and is presently classified as exhibiting reduced reproductive capacity. It is, therefore, of interest to update information on cod spawning activity and get an understanding of the dispersal of eggs. As to evaluate spawning, data were analysed from dedicated egg surveys in the Kattegat between 2004 and 2006. Genetically identified cod eggs confirmed that cod were spawning in the studied area during the sampling period. The estimated daily egg production was high in the south-eastern part of the surveyed area (~20 eggs m-2 d-1) while it was low (0–5 eggs m-2 d-1) in the central and northern part. This emphasises the importance of the southernmost spawning area in the Kattegat, close to the Öresund. A process oriented model was used to investigate transport of cod eggs and early larvae in relation to egg density as well as how the interannual variation of retention and dispersal is related to the meteorological forcing. The model results clearly indicated that transport is highly dependent on the egg density; lighter eggs are transported northwards, whereas heavier eggs are retained to a larger extent or are transported southwards. An optimum of retention is defined in the density range 1023-1026 kg m-3. Combining the model results of the amount of retention, distribution and sedimentation with observations of vertical distribution of cod-like eggs in the range 1017-1022 kg m-3, suggests that gadoid eggs are mainly retained in the southern Kattegat, but also simultaneously dispersed northwards. Further investigation showed that interannual variation of retention, transport and sedimentation are highly correlated to the changes of local wind forcing. Strong westerly winds induce southward transport and high sedimentation while weak variable winds tend to retain eggs in the spawning area. The results of this study provide a starting point for future studies of spawning and life history characteristics of the Kattegat cod, and also in studies designed to entangle the stock complex in the Kattegat-Öresund-Belt area. Climatic variation affecting the ocean conditions for passive drift of eel larvae is one of the factors suspected to be related to the decline of eel recruitment. A simple Lagrangian model was used to simulate the passive drift of the European eel (Anguilla anguilla) leptocephalus larvae from the spawning area in the Sargasso Sea to the European shelf (20°W). The simulation utilised the velocity data from a reanalysis of ocean climate, the Simple Ocean Data Assimilation (SODA 2.1.6), for the period from 1958 to 2008. The period which was modelled covers the time of a regime shift in eel recruitment in the 1980s. The average drift time and latitudinal distribution of the arrival of larvae (particles in the model) was explored for a range of constant depth levels and instantaneous mortalities. The model showed that the proportion of eel larvae carried by the North-east Atlantic current to northern latitudes of arrival was greater before 1970 whereas there was an increase in amount of eel larvae being entrained into the southbound current branches in later part of simulation. The overall success of drift from the spawning area to the eastern Atlantic clearly contradicts that this could explain the dramatic recruitment decline.
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| 10. |
- Pacariz, Selma, 1973, et al.
(författare)
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Nutrient-driven poleward expansion of the Northeast Atlantic mackerel (Scomber scombrus) stock: A new hypothesisNutrient-driven expansion of the mackerel stock : Nutrient-driven expansion of the mackerel stock
- 2016
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Ingår i: Elementa: Science of Anthropocene. - : University of California Press. - 2325-1026. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The Northeast Atlantic mackerel (Scomber scombrus) stock has increased and expanded its summer feeding migration west- and northwards since 2006, entailing large geopolitical challenges for the countries harvesting this species. A common perspective is that climatic warming opens up new regions for biota in the north. It has also been suggested that the presently large pelagic fish stocks deplete prey resources in the eastern North Atlantic during their summer feeding phase, forcing the stocks west towards the Irminger Sea in their search for food. Here, we suggest that the declining nutrient (silicate) concentrations observed along the northern European continental slope reduce primary and thus secondary production, exacerbating food scarceness in the east and adding to the incentive to migrate westward. The new westward feeding route requires that the fish cross the Iceland Basin, which during the summer season quickly becomes nutrient-depleted and thus might act as a barrier to migration after the spring bloom. Using mackerel and zooplankton abundance data from the International Ecosystem Summer Surveys in the Nordic Seas, we suggest that the oligotrophic waters in the central Iceland Basin force the fish to migrate through a narrow ‘corridor’ along the south Iceland shelf, where nutrients are replenished and both primary and secondary production are higher.
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