Discrimnation of herring populations in a northern Norwegian fjord: genetic and biological aspects

From a trawl survey in a fjord system in northern Norway, it has been possible to separate catches of herring into two distinct groups characterized by different number of vertebrae (VS). Low- vertebral herring (VS = 52-55) belong to a local stock of spring-spawning fjord stock called the Balsfjord herring. High-vertebral herring (VS = 56-60) belong to an immigrating population of Atlanto- Scandian herring spawned off the Norwegian coast. The separation between the stocks was verified by genetic analysis of herring samples using enzyme electrophoresis. The Balsfjord -herring is characterized by a very high frequency ( 0.93) of a rare allele (designated 110) at the LDH-2 locus which is expressed in white muscle tissue. In comparison, this allele is usually not found (frequency < 0. 01) in samples of Atlanto-Scandian herring. The discrimination between the two stocks in Balsfjord was, however, evident from the biological data obtained (age distribution, VS, mean length and length distributions) as well as the genetic characters investigated. In addition, the Balsfjord herring, especially at mature stage, seem to be distributed at 60-200 m depth and was caught by using bottom trawl. The Atlanto- Scandian herring, mainly 2 or 3 years old, was found in the upper water layer (0-60 m). The genetic data indicate very limited or no gene flow between the two herring stocks in Balsfjord. This fjord system, therefore, offers unique possibility to study interaction and isolating mechanisms with regards to marine fish stocks

COBRA: a new European research project for organic plant breeding

Development of organic plant breeding and seed production will have a valuable impact on organic plant production. Breeding of plant material adapted for organic agriculture is crucial in order to cope with stresses such as climate change, weeds and seed borne diseases. Conventional varieties may not meet the specific needs of organic agriculture. The use of plant material adapted to conditions of organic agriculture will have a positive effect on the productivity and sustainability of organic crop production

Hyperkahler Metrics from Periodic Monopoles

Relative moduli spaces of periodic monopoles provide novel examples of Asymptotically Locally Flat hyperkahler manifolds. By considering the interactions between well-separated periodic monopoles, we infer the asymptotic behavior of their metrics. When the monopole moduli space is four-dimensional, this construction yields interesting examples of metrics with self-dual curvature (gravitational instantons). We discuss their topology and complex geometry. An alternative construction of these gravitational instantons using moduli spaces of Hitchin equations is also described.Comment: 23 pages, latex. v2: an erroneous formula is corrected, and its derivation is given. v3 (published version): references adde

Recruitment processes in West Greenland waters: With special focus on Greenland halibut ( Reinhardtius hippoglossoides, W.)

The topic of this thesis is recruitment processes in Greenland Halibut (Reinhardtius hippoglossoides) in West Greenland waters. The focal point is Greenland halibut’s early life history from oocytes in the female ovary - to larvae living in the pelagic - to juveniles on the sea bottom. These early life stages are examined in four studies: Ovary and oocyte development in adult female Greenland halibut was studied in Davis Strait, Disko Bay and Baffin Bay. The objective of this study was to track and compare ovary development from winter to autumn from the inshore fjords of Disko Bay, Baffin Bay and the presumed spawning area in Davis Strait. Results showed that maturity was much more progressed in Davis Strait compared to the two other areas. Furthermore, almost all adult female fish in Davis Strait showed signs of maturation while only a fraction of the larger females (>80 cm length) were mature in Disko and Baffin Bay. A large proportion of the Greenland halibut in Disko and Baffin Bay did not appear to begin the maturation cycle until very late in their life history and/or were repeat spawners with a multiyear maturation cycle. Thus the observations from Disko and Baffin Bay support the theory that Greenland halibut can have a prolonged adolescent phase. The result from the study also strongly indicated that Davis Strait was the only major spawning area in West Greenland. Larvae distribution and growth of Greenland halibut and Sandeel (Ammodytes sp.) was studied across the West Greenland shelf. The objective of this study was to analyse spatial distribution and growth during three periods May, June and July and relate these to cross shelf variability in biological and hydrographical conditions in order to identify areas of special importance for larval growth and survival. Results showed that in May small Greenland halibut larvae, some still with small remains of the yolk-sac, were primarily distributed offshore in Davis Strait. Their distribution coincided with their prey resources while some vagrant larvae were dispersed to areas with less food, which likely resulted in higher mortality rates. Consequently, the emergence of first feeding Greenland halibut larvae matched their prey in time and space which is believed to be crucial for survival success at this critical stage in their development. From June to July Greenland halibut larvae gradually shifted their distribution from the bank slopes to the deeper parts of the slope near the shelf break. The lack of clear and well-defined frontal zones made it difficult to evaluate the hydrographical processes that had significance for larval distribution patterns. Greenland halibut larvae did, however, show preference for stratified water masses. Growth analysis of Greenland halibut larvae was only possible for July and showed higher growth was observed at stations positioned in frontal zones suggesting that growth was significantly influenced by the level of frontal activity. The study also included distribution and growth comparisons with sandeel. The larvae of sandeel was considerably more associated to the banks and bank slopes than Greenland halibut larvae in all three months (May-July), however in June, the two species coexisted considerably in the same areas of the cross shelf. The growth analysis showed that sandeel and Greenland halibut larvae showed opposite responses to some hydrographical conditions and prey abundance. Sandeel growth decreased with increasing frontal activity and increased with increasing prey biomass. The later observation suggests that sandeel growth was limited by food availability. Cross shelf variation in growth in Greenland halibut larvae showed that enhanced growth was observed at some stations where they were most abundant. Overall, however, there was no clear association between larval growth and larval abundances for neither Greenland halibut nor sandeel larvae. The observed patchiness in larval distribution could therefore also be a result of retention mechanisms and / or predation mortality. The feeding ecology of pelagic Greenland halibut and sandeel larvae was studied across the West Greenland shelf. The aim of this study was to analyse and compare feeding ecology of coexisting Greenland halibut and sandeel larvae. Diet analysis and prey preference considerations were used to assess spatial variation in prey availability and feeding. The hypothesis was that feeding conditions are optimal in central areas of fish larval distribution, and that timing of larval emergence is synchronised with prey availability. The study showed that for both species copepods were the main prey items and that absolute size of preferred prey increased during larval ontogeny. However, preferred copepod size in relation to larval length differed markedly between Greenland halibut and sandeel. In Greenland halibut the relative size of the prey declined during growth of the larvae while for sandeel the relative size of prey remained constant at a level of 2.7% of larval length. This led to a reduction in prey niche overlap between the two species as Greenland halibut and sandeel larvae increased in size. The available prey copepod biomass differed distinctly across the shelf area. In May, Greenland halibut prey density was highest in the off-shelf area in Davis Strait. In June and July, the prey rich areas for both species were mainly located on the slopes of the banks and at the shelf break area. In these areas gut fullness was higher than in neighbouring areas, suggesting that the food resource could be scarce. The feeding ecology of Greenland halibut and sandeel could explain why larval abundance indices for the two species historically have shown opposite responses to annual environmental conditions and total zooplankton occurrence. Drift and growth of Greenland halibut from eggs throughout the pelagic larval stage was tracked from sub-population spawning areas in Davis Strait, Baffin Bay, East Greenland and West Iceland by combing drift- and individual-based egg and larval temperature dependent growth models. Model results were compared to survey results and the settling process was followed at Store Hellefisk Bank in West Greenland. The aim of this study was to evaluate spatio-temporal distribution of small first feeding and large settling larvae, and the between metapopulations. Results showed that egg and larvae can drift for long distances and that the exchange of individuals among the geographically-separated sub-populations could be important for metapopulation dynamics. Larvae from the spawning area in Davis Strait were primarily (>60%) transported to Canadian waters. Only larvae from the eastern part of the spawning area in Davis Strait remained in West Greenland. All larvae from the East Greenland spawning area were transported south of Cape Farewell and to West Greenlandic (82%) or Canadian (18%) waters. From the West Icelandic spawning areas larvae either, depending on the spatial location on the emergence first feeding larvae, drifted to East Greenland (45-53%), West Greenland (19−34%) or Northern Iceland (21−28%) or remained (>98%) in Iceland waters. In Baffin Bay low water temperatures resulted in very slow development rates and eggs probably never hatched. The surveys showed that in West Greenland larvae settling started in August and continued in September but the settling peak period could not be determined. The study in the two areas of Hellefisk Bank showed that juveniles of age 1 and 2+ almost exclusively occurred in one area while the 0-group was equally distributed in both areas. In the area of high juvenile age 1 and 2+ abundance the condition and stomach fullness was significantly higher than in the low abundance areas. Nursery ground processes within the first year clearly restricted the successful nursery area to a more specific bottom habitat types. The concentrating of juveniles into specific nursery areas implies that juvenile densities may approach the carrying capacity of their habitats in years when settlement is high, which would dampen the annual variability in year class strength of Greenland halibut

Comments on gluon scattering amplitudes via AdS/CFT

In this article we consider n gluon color ordered, planar amplitudes in N=4 super Yang Mills at strong 't Hooft coupling. These amplitudes are approximated by classical surfaces in AdS_5 space. We compute the value of the amplitude for a particular kinematic configuration for a large number of gluons and find that the result disagrees with a recent guess for the exact value of the amplitude. Our results are still compatible with a possible relation between amplitudes and Wilson loops. In addition, we also give a prescription for computing processes involving local operators and asymptotic states with a fixed number of gluons. As a byproduct, we also obtain a string theory prescription for computing the dual of the ordinary Wilson loop, Tr P exp[ i\oint A ], with no couplings to the scalars. We also evaluate the quark-antiquark potential at two loops.Comment: 27 pages, 9 figures,v3:minor correction

A Conformally Invariant Holographic Two-Point Function on the Berger Sphere

We apply our previous work on Green's functions for the four-dimensional quaternionic Taub-NUT manifold to obtain a scalar two-point function on the homogeneously squashed three-sphere (otherwise known as the Berger sphere), which lies at its conformal infinity. Using basic notions from conformal geometry and the theory of boundary value problems, in particular the Dirichlet-to-Robin operator, we establish that our two-point correlation function is conformally invariant and corresponds to a boundary operator of conformal dimension one. It is plausible that the methods we use could have more general applications in an AdS/CFT context.Comment: 1+49 pages, no figures. v2: Several typos correcte

Homogeneity in prediction of survival probabilities for subcategories of hipprosthesis data : the Nordic Arthroplasty Register Association, 2000–2013

Introduction: The four countries in the Nordic Arthroplasty Register Association (NARA) share geographic proximity, culture, and ethnicity. Pooling data from different sources in order to obtain higher precision and accuracy of survival-probability estimates is appealing. Nevertheless, survival probabilities of hip replacements vary between the countries. As such, risk prediction for individual patients within countries may be problematic if data are merged. In this study, our primary question was to address when data merging for estimating prosthesis survival in subcategories of patients is advantageous for survival prediction of individual patients, and at what sample sizes this may be advised. Methods: Patients undergoing total hip replacements for osteoarthritis between January 1, 2000 and December 31, 2013 in the four Nordic countries were studied. A total of 184,507 patients were stratified into 360 patient subcategories based on country, age-group, sex, fixation, head size, and articulation. For each patient category, we determined the sample size needed from a single country to obtain a more accurate and precise estimate of prosthesis-survival probability at 5 and 10 years compared to an estimate using data from all countries. The comparison was done using mean-square error. Results: We found large variations in the sample size needed, ranging from 40 to 2,060 hips, before an estimate from a single Nordic country was more accurate and precise than estimates based on the NARA data. Conclusion: Using pooled survival-probability estimates for individual risk prediction may be imprecise if there is heterogeneity in the pooled data sources. By applying mean-square error, we demonstrate that for small sample sizes, applying the larger NARA database may provide a more accurate and precise estimate; however, this effect is not consistent and varies with the characteristics of the subcategory

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure