Entity

Time filter

Source Type

Visby, Sweden

Nissling A.,Gotland University | Florin A.-B.,Swedish University of Agricultural Sciences | Thorsen A.,Norwegian Institute of Marine Research | Bergstrom U.,Swedish University of Agricultural Sciences
Journal of Sea Research | Year: 2013

In the brackish water Baltic Sea turbot spawn at ~. 6-9. psu along the coast and on offshore banks in ICES SD 24-29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378-3474. oocytes/g somatic weight) compared to those from SD 25 (2343. oocytes/g somatic weight), with no difference in egg size (1.05. ±. 0.03. mm diameter and 46.8. ±. 6.5. μg dry weight; mean. ±. sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish. © 2012 Elsevier B.V. Source


Ivanell S.,KTH Royal Institute of Technology | Ivanell S.,Gotland University | Mikkelsen R.,Technical University of Denmark | Sorensen J.N.,Technical University of Denmark | Henningson D.,KTH Royal Institute of Technology
Wind Energy | Year: 2010

The aim of the present paper is to obtain a better understanding of the stability properties of wakes generated by wind turbine rotors. To accomplish this, a numerical study on the stability of the tip vortices of the Tjaereborg wind turbine has been carried out. The numerical model is based on large eddy simulations of the Navier-Stokes equations using the actuator line method to generate the wake and the tip vortices. To determine critical frequencies, the flow is disturbed by inserting harmonic perturbations, giving rise to spatially developing instabilities. The results show that the instability is dispersive and that growth arises only for some specific frequencies and type of modes, in agreement with previous instability studies. The result indicates two types of modes; one where oscillations of neighboring vortex spirals are out of phase and one where oscillations in every vortex spiral in phase. The mode with spirals out of phase results in the largest growth with the main extension of the disturbance waves in radial and downstream directions. The out-of-phase disturbance leads to vortex pairing once the development leaves the linear stage. The study also provides evidence of a relationship between the turbulence intensity and the length of the near wake. The relationship, however, needs to be calibrated against measurements. Copyright © 2010 John Wiley & Sons, Ltd. Source


Eight Andean species of Symplocos Jacq. (Symplocaceae) are described as new to science. They include: S. condorensis B. Sthl, S. neillii B. Ståhl, and S. vanderwerffii B. Sthl from southern Ecuador (Zamora-Chinchipe and Morona-Santiago provinces); S. golondrinae B. Sthl from northern Ecuador (Carchi Province); S. guacamayensis B. Sthl from east-central Ecuador (Napo Province); S. fragilis B. Sthl and S. ovata B. Sthl from northern Peru (Amazonas Department); and S. dolichopoda B. Sthl from southern Peru (Cusco Department). Symplocos spruceana (Miers) Grke and S. nuda Humb. & Bonpl. are reported as new to Ecuador and Peru, respectively. © Missouri Botanical Garden 2010. Source


Rosenqvist G.,Norwegian University of Science and Technology | Rosenqvist G.,Gotland University | Berglund A.,Uppsala University
Journal of Fish Biology | Year: 2011

Male pregnancy in the family Syngnathidae (pipefishes, seahorses and seadragons) predisposes males to limit female reproductive success; sexual selection may then operate more strongly on females and female sexual signals may evolve (sex-role reversal). A bewildering array of female signals has evolved in Syngnathids, e.g. skin folds, large body size, colouration, markings on the body and elaborate courtship. These female sexual signals do not seem quantitatively or qualitatively different from those that evolve in males in species with conventional sex roles where males provide females or offspring with direct benefits. In several syngnathid species, males also evolve ornaments, females are choosy in addition to being competitive and males compete as well as choosing partners. Thus, sex roles form a continuum, spanning from conventional to reversed within this group of fishes. Cases are presented here suggesting that stronger sexual selection on females may be most extreme in species showing classical polyandry (one male mates with several females, such as many species where males brood their eggs on the trunk), intermediate in polygynandrous species (males and females both mate with more than one partner, as in many species where males brood their eggs on the tail) and least extreme, even exhibiting conventional sex roles, in monogamous species (one male mates solely with one female, as in many seahorses and tropical pipefishes). At the same time caution is needed before unanimously establishing this pattern: first, the connection between mating patterns, strength of sexual selection, sex roles and ornament expression is far from simple and straightforward, and second, knowledge of the actual morphology, ecology and behaviour of most syngnathid species is scanty. Basically only a few Nerophis, Syngnathus and Hippocampus species have been studied in any detail. It is known, however, that this group of fishes exhibits a remarkable variation in sex roles and ornamentation, making them an ideal group for the study of mating patterns, sexual selection and sexually selected signals. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles. Source


Sellers M.,Online Alchemy Inc. | Sellers M.,Gotland University
Biologically Inspired Cognitive Architectures | Year: 2013

A new model of emotions that is applicable to both biological and artificial agents is proposed. The description includes theoretical foundations, internal representation, and the role of emotions in cognition. This model is based on definitions of emotions in valence and arousal space coupled with an adaptation of Maslow's hierarchy and other ideas. The resulting architecture provides for a significantly more expressive range and organization of represented emotional experience compared to other models. Requirements for a satisfactory general computational theory of emotions are applied to the new theory and analyzed in terms of (i) neurological and psychological plausibility, (ii) range and complexity of human emotional experience, (iii) applicability to learning, memory, behavior, and decision-making, and (iv) consistency with well-accepted models and general facts about emotions. The model is implemented and studied through simulations of virtual agent-based systems. Presented results support the model's applicability to perception, action selection, learning, and memory in virtual agents capable of human-like behavior. Paradigms and predictions allowing for further validation of the new model and emotion theories in general are discussed. © 2012 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations