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Libungan L.A.,University of Iceland | Slotte A.,Norwegian Institute of Marine Research | Slotte A.,Hjort Center for Marine Ecosystem Dynamics | Otis E.O.,Alaska Department of Fish and Game | Palsson S.,University of Iceland
Polar Biology | Year: 2016

Pacific herring (Clupea pallasii) is divided into three subspecies: two in northeast Europe and one in the north Pacific Ocean. Genetic studies have indicated that the populations in northeast Europe have derived from the northwest Pacific herring recently, or during the last 10–15 kyr, and that they are distinct from the population in the northeast Pacific. In addition, hybridization between the Pacific herring and the Atlantic herring has been documented. Otolith variation has been considered to be largely affected by environmental variation, but here we evaluate whether the genetic differentiation is reflected in otolith shape differences. A clear difference in otolith shape was observed between the genetically differentiated herring species Clupea harengus from the Atlantic and C. pallasii. The otolith shape of C. p. suworowi in the Barents Sea was different from the shape of C. pallasii in northern Norway and C. p. pallasii from the Pacific. Populations of C. p. pallasii, sampled east and west of the Alaska Peninsula, which belong to two genetically different clades of the C. p. pallasii in the Pacific Ocean, show a clear difference in otolith shape. C. p. suworowi and the local C. pallasii peripheral population in Balsfjord in northern Norway are more similar to the northwest Pacific herring (C. p. pallasii) than to the northeast Pacific herring (C. p. pallasii), both genetically and in otolith shape. The Balsfjord population, known to be influenced by introgression of mtDNA from the Atlantic herring, does not show any sign of admixture in otolith shape between the two species. A revised classification, considering the observed genetic and morphological evidence, should rather group the northwest Pacific herring in the Bering Sea together with the European populations of C. pallasii than with the northeast Pacific herring in the Gulf of Alaska. © 2016 Springer-Verlag Berlin Heidelberg Source

Certain G.,SLU Institute for Coastal Research | Certain G.,Norwegian Institute of Marine Research | Certain G.,Norwegian Institute for Nature Research | Planque B.,Norwegian Institute of Marine Research | Planque B.,Hjort Center for Marine Ecosystem Dynamics
ICES Journal of Marine Science | Year: 2015

Biodiversity is an increasingly important issue for the management of marine ecosystems. However, the proliferation of biodiversity indices and difficulties associated with their interpretation have resulted in a lack of clearly defined framework for quantifying biodiversity and biodiversity changes in marine ecosystems for assessment purpose. Recent theoretical and numerical developments in biodiversity statistics have established clear algebraic relationships between most of the diversity measures commonly used, and have highlighted those that most directly relates to the concept of biological diversity, terming them "true" diversity measures. In this study, we implement the calculation of these "true" diversity measures at the scale of a large-marine ecosystem, the Barents Sea. We applied hierarchical partitioning of biodiversity to an extensive dataset encompassing 10 years of trawl-surveys for both pelagic and demersal fish community. We quantify biodiversity and biodiversity changes for these two communities across the whole continental shelf of the Barents Sea at various spatial and temporal scales, explicitly identifying areas where fish communities are stable and variable. The method is used to disentangle areas where community composition is subject to random fluctuations from areas where the fish community is drifting over time. We discuss how our results can serve as a spatio-temporal biodiversity baseline against which new biodiversity estimates, derived from sea surveys, can be evaluated. © 2015 International Council for the Exploration of the Sea. All rights reserved. Source

Siegelman-Charbit L.,Norwegian Institute of Marine Research | Siegelman-Charbit L.,University Pierre and Marie Curie | Planque B.,Norwegian Institute of Marine Research | Planque B.,Hjort Center for Marine Ecosystem Dynamics
Marine Ecology Progress Series | Year: 2016

The presence of a dense layer of organisms in the mesopelagic zone is a ubiquitous feature of the world oceans, and these organisms may constitute a major component of marine biomass worldwide. Many mesopelagic organisms perform light-dependent diel vertical migration. It has been hypothesised that extreme light regimes encountered at high latitudes may disturb these migration patterns and thereby limit the northern expansion of mesopelagic fauna into the Arctic. Using hydroacoustic data collected during 4 surveys conducted in the open Norwegian Sea during the summer season, we evaluated if the key features of mesopelagic fauna reported worldwide (high density and diel vertical migration) are also observed in the high latitudes of the Northeast Atlantic. The results confirm that the high-latitude Northeast Atlantic hosts a high density of mesopelagic fauna which performs daily migration patterns similar to those reported in other regions. They also support the limiting effect of photoperiod on its potential biomass. These results stress the need for thorough studies on the abundance, biodiversity and trophic ecology of the mesopelagic fauna in this region. © Institute of Marine Research, Norway 2016. Source

Kolding J.,University of Bergen | Kolding J.,Hjort Center for Marine Ecosystem Dynamics | Bundy A.,Bedford Institute of Oceanography | Van Zwieten P.A.M.,Wageningen University | Plank M.J.,University of Canterbury
ICES Journal of Marine Science | Year: 2016

A global assessment of fishing patterns and fishing pressure from 110 different Ecopath models, representing marine ecosystems throughout the world and covering the period 1970-2007, show that human exploitation across trophic levels (TLs) is highly unbalanced and skewed towards low productive species at high TLs, which are around two TLs higher than the animal protein we get from terrestrial farming. Overall, exploitation levels from low trophic species were <15% of production, and only 18% of the total number of exploited groups and species were harvested >40% of their production. Generally, well-managed fisheries from temperate ecosystems were more selectively harvested at higher exploitation rates than tropical and upwelling (tropical and temperate) fisheries, resulting in potentially larger long-term changes to the ecosystem structure and functioning. The results indicate a very inefficient utilization of the food energy value of marine production. Rebuilding overfished components of the ecosystem and changing focus to balancing exploitation across a wider range of TLs, i.e. balanced harvesting, has the potential to significantly increase overall catches from global marine fisheries. © 2015 International Council for the Exploration of the Sea 2015. Source

Kolding J.,University of Bergen | Kolding J.,Hjort Center for Marine Ecosystem Dynamics | Jacobsen N.S.,Technical University of Denmark | Andersen K.H.,Technical University of Denmark | van Zwieten P.A.M.,Wageningen University
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2016

Under the ecosystem approach to fisheries, an optimal fishing pattern is one that gives the highest possible yield while having the least structural impact on the community. Unregulated, open-access African inland fisheries have been observed to sustain high catches by harvesting a broad spectrum of species and sizes, often in conflict with current management regulations in terms of mesh and gear regulations. Using a size- and trait-based model, we explore whether such exploitation patterns are commensurable with the ecosystem approach to fisheries by comparing the impacts on size spectrum slope and yield with the different size limit regimes employed in the Zambian and Zimbabwean sides of man-made Lake Kariba. Long-term multispecies data under fished and unfished conditions are used to compare and validate the model results. Both model and observations show that the highest yields and low structural impact on the ecosystem are obtained by targeting small individuals in the community. These results call for a re-evaluation of the size-based management regulations that are ubiquitous in most fisheries. © 2016 Published by NRC Research Press. All Rights Resreved. Source

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