Papers by Michaela Aschan
Frontiers in Aquaculture, Oct 31, 2023
9 s., 2009
We document the spatial patterns found in the Barents Sea fish community in relation to environme... more We document the spatial patterns found in the Barents Sea fish community in relation to environmental parameters, analysing data from the ecosystem surveys covering the Norwegian part of the Barents Sea during 2004-2008 and comparing with earlier investigations of the deeper areas from the period 1992-2004. Changes in the ecosystem, expected on the basis of changing climate and harvest regimes may often go undetected due to strong focus on oceanography and commercial species of monitoring programs. Fish species that are not targeted by fishery are included in the analyses, providing valuable, additional ecological information on structural alterations. We identified species assemblages associated with different water masses and range of productivity of sea areas. Major changes in the structure of the fish community occur in this previously thought healthy, resilient and well-managed large marine ecosystem. The spatio-temporal analyses of the Barents Sea survey data from this decade shows that a new fish community structure is in place compared to the general community structure of the previous decades. An ecological regime shift in the 90-ies might be speculated. The change is concurrent with a climatic regime shift and may be persistent.
24 s., 1997
Trawl surveys for shrimp (Pandalus borealis ) have been conducted annually in the Barents Sea and... more Trawl surveys for shrimp (Pandalus borealis ) have been conducted annually in the Barents Sea and the Svalbard area since 1980 by Norwegian research institutes. The surveys have been conducted in the period April to September for a duration of 25 to 97 d·ays each year. Until 1992 the Institute of Marine Research in Bergen (IMR) carried out the investigations, and thereafter the Norwegian Institute of Fisheries and Aquaculture Ltd. (Fiskeriforskning) in · Tromsø has been doing the work. All together four different vessels have been use~ The.ttawl used for sampling, a 1800 meshes modified commercial trawl, has been the same. throughout the period, although with m.odifications of both the ground gear and the rigging. The modifications have ~ad a considerable influence on sampling performance over time. . . Th~ sn;tdy ·area in ·sval~~.ltd is stratifled aecording to deptb and latitud~ whil~ th~ study area in .the Barents._Sea"is stratitled based ~n ge.ographical areas of assum!!d homogenq:us .. density of shrimp together with a s~bjective·divisiori o~~e area into fi~hlng grounds. ·. · . Three different.~pproaches to survey d~sigil have been usedrandom.stratifiedtrawl stations, . fixed trawl stations in a niodified regular grid within a stratification of-the area.and fixed trawl ·. . . statiohs iø a_ depth siratified syst~m. A stUdy ha8 been: undertaicen to c8.Iculat~ an· optimum .. sampling density with respect to a desired level of p.recision. · The survey data are pritD.arily ~sed to calculate indices of shrimp abundance, both for the whole area and for a set of sub areas. Data on carapace length distribution is used to separate age groups and to study size and growth of the year cl~ses in different sub areas. INTRODUCTION AND IDSTORY Since 1992 the Norwegian Institute ofFisheries and Aquacultre Ltd. (Fiskeriforskning) in Tromsø has had the national responsibility for the research on shrimp (Panda/us borealis ) north of 62°N. The research is don~ in close cooperation with the Norwegian College of Fisheries Science at Øle University of 'l)omsø .. There is ~so a close scientific cooperation with the . ·Institute of Marine Research in Bergen .(JMR) which ~the Period 1980_ -· 199t conducted the . · ·shrlmp research in the Barents Sea and the Svalbard area, f.e. the No~egian, Russian and Svalbard Exclusive Economic Zones (EE.V s) north of 62°N. The Polar Research Institute of .-.
19 s., 2000
The shrimp spawn in autumn and the eggs are carried as out roe by the females until spring when t... more The shrimp spawn in autumn and the eggs are carried as out roe by the females until spring when the larvae hatch. Within a period of 2-3 months the shrimp larvae settle to the bottom. Today's assessment and forecast of the shrimp stock productivity and potential fishing yields is weak. This is partly due to poor knowledge on population dynamics from hatching and till the shrimp are caught in the fishery at the age of three or four years in the. Since 1995 juvenile shrimp has been caught by a net attached to the underbelly of the survey trawl during the annual cruise in the Barents Sea. The abundance of settled shrimp larvae varies in time and space. The recruitment to the fishery has been quite stable with the exception of the 1996 year-class that was observed as l+ but has not been registered since. We study the annual settlement and survivor of juveniles until recruiting to the fishery. The spatial and temporal distribution as well as density of the four youngest year-classes are studied in relation to temperature, depth, shrimp stock abundance and presence of predating cod in the Barents Sea.
The goal of an ecosystem based approach to management is to preserve robust ecosystems that can c... more The goal of an ecosystem based approach to management is to preserve robust ecosystems that can cope with the environmental pressure imposed by human activities. Vulnerable ecosystems exposed to strong environmental perturbation are at high risk of large impact. Ecosystem based management can mitigate impact by dealing with ecosystem properties that influence vulnerability. The challenge is to identify relevant ecosystem properties that can be effectively integrated in assessment and decision making so as to operationalize ecological robustness and resilience. Here we present the approach used in the project BarEcoRe to quantify, evaluate and integrate an ensemble of structural properties affecting ecosystem adaptability and sensitivity to environmental change. The ecosystem properties, which include functional diversity and redundancy, and food web compartmentalization, were quantified based on data from the Norwegian and Russian Barents Sea ecosystem surveys. The chosen structural ecosystem properties can be combined with early warning signals estimated from time series to monitor robustness and resilience of managed ecosystems and to guide decision making.
Ices Journal of Marine Science, Oct 24, 2019
Marine mammals are important players in the Barents Sea ecosystem but their food web role is poor... more Marine mammals are important players in the Barents Sea ecosystem but their food web role is poorly known. We identify food web-related characteristics within and between phylogenetic groups for 19 marine mammals. As a group, they are directly connected to the most central species in the Barents Sea (i.e. cod and haddock) and consume over half of the available species. Pinnipeds are the most homogenous phylogenetic group with high omnivory and many prey species. Mysticetes are split between well-connected species with high omnivory like the humpback whale, and peripheral specialists like the blue whale. Some species are consistently clustered together based on food web-derived indices, suggesting
22 s., 1993
The results of the Russian and Norwegian surveys for shrimp, Pandalus borealis, in the Barents Se... more The results of the Russian and Norwegian surveys for shrimp, Pandalus borealis, in the Barents Sea in spring and the Svalbard area in autumn 1992 are presented in this paper. The survey results are presented by nation but the discussion is given combined. Biomass, sizeand sex frequency will be presented for subareas. The data from both countries show similar trends. They indicate that the shrimp biomass in the Barents Sea has decreased with approximately 15 % since 1991. The Hopen area and the Bear Island trench area show the largest reduction. However, there is a slight increase in the biomass north of 75°30'N, this may be due to warmer sea temperatures. The Svalbard area was investigated only by the Norwegians. New areas were covered north of Svalbard. An increase in the biomass is observed in the Svalbard area.
Proceedings of The Royal Society B: Biological Sciences, Apr 7, 2021
As temperatures rise, motile species start to redistribute to more suitable areas, potentially af... more As temperatures rise, motile species start to redistribute to more suitable areas, potentially affecting the persistence of several resident species and altering biodiversity and ecosystem functions. In the Barents Sea, a hotspot for global warming, marine fish from boreal regions have been increasingly found in the more exclusive Arctic region. Here, we show that this shift in species distribution is increasing species richness and evenness, and even more so, the functional diversity of the Arctic. Higher diversity is often interpreted as being positive for ecosystem health and is a target for conservation. However, the increasing trend observed here may be transitory as the traits involved threaten Arctic species via predation and competition. If the pressure from global warming continues to rise, the ensuing loss of Arctic species will result in a reduction in functional diversity.
Zenodo (CERN European Organization for Nuclear Research), Mar 25, 2021
This report contains an evaluation of the university-level certificate programme in "Marine Manag... more This report contains an evaluation of the university-level certificate programme in "Marine Management and Innovation" (SVF-6013) that was developed and ran as part of the FarFish project. The programme was organised by University of Tromsø (UiT-The Arctic University of Norway) and ran from 9-13 th March 2020. A total of 22 students from all across the world attended the programme onsite in Tromsø, and many more watched live streaming from the lectures. The lectures were also recorded and have been available at the FarFish website since then. Throughout the week, participants were trained on topics such as international ocean governance, traceability, value and supply chains, food safety and economics. The training consisted of lectures, group work, field trips and final thesis. Among the 29 participants attending the programme, eight took the exam to be able to receive the certificate, and they all passed. The project therefore reached its goal of graduating at least five participants from the programme. The exams, essays with self-chosen topics, contribute to the programme's academic outcome, and
Fish and Fisheries, 2017
We present a framework for Results Based Management (RBM) of commercial fisheries. The core idea ... more We present a framework for Results Based Management (RBM) of commercial fisheries. The core idea of RBM is to reduce micro-management by delegating management responsibility to resource users. The RBM framework represents an industrial organization approach to comanagement and comprises three defining processes, conducted by three independent "agents": 1) an "authority" defines specific and measurable and achievable objectives (outcome targets, OTs) for the utilization of fisheries resources, 2) resource user organizations (termed "operators") take responsibility for achieving these OTs and provide documentation that 3) allows independent "auditors" to evaluate the achievement of OTs. Using incentive mechanisms, notably deregulation, RBM grants operators the flexibility to develop and implement innovative and cost-effective ways to achieve OTs. The feasibility of implementing RBM in five European fisheries was investigated in cooperation with relevant stakeholders through artificial planning processes and computer simulations. The operators involved were enthusiastic, and new management plans were drafted based on the framework. These included socioeconomic OTs in addition to traditional stock objectives, encompassing an ecosystem approach. Several issues are in need of further research in order to consolidate the approach and prepare the ground for practical implementation, including: the specification of the legal and regulatory framework required to underpin RBM, details of transitional arrangements when shifting towards RBM (including cost-sharing) and the development of necessary organizational capacity for operators. Initially, we therefore envisage the framework being applied to high value single species fisheries, with a limited number of participants, which are adequately represented by a competent organization.
PLOS ONE, 2018
When facing environmental change and intensified anthropogenic impact on marine ecosystems, exten... more When facing environmental change and intensified anthropogenic impact on marine ecosystems, extensive knowledge of how these systems are functioning is required in order to manage them properly. However, in high-latitude ecosystems, where climate change is expected to have substantial ecological impact, the ecosystem functions of biological species have received little attention, partly due to the limited biological knowledge of Arctic species. Functional traits address the ecosystem functions of member species, allowing the functionality of communities to be characterised and the degree of functional redundancy to be assessed. Ecosystems with higher functional redundancy are expected to be less affected by species loss, and therefore less sensitive to disturbance. Here we highlight and compare typical functional characteristics of Arctic and boreal fish in the Barents Sea and address the consequences of a community-wide reorganization driven by climate warming on functional redundancy and characterization. Based on trait and fish community composition data, we assessed functional redundancy of the Barents Sea fish community for the period 2004-2012, a period during which this northern region was characterized by rapidly warming water masses and declining sea ice coverage. We identified six functional groups, with distinct spatial distributions, that collectively provide a functional characterization of Barents Sea fish. The functional groups displayed different prevalence in boreal and Arctic water masses. Some functional groups displayed a spatial expansion towards the northeast during the study period, whereas other groups showed a general decline in functional redundancy. Presently, the observed patterns of functional redundancy would seem to provide sufficient scope for buffering against local loss in functional diversity only for the more speciose functional groups. Furthermore, the observed functional reconfiguration may affect future ecosystem functioning in the area. In a period of rapid environmental change, monitoring programs integrating functional traits will help inform management on ecosystem functioning and vulnerability.
Sarsia, 1990
Page 1. EFFECTS OF CHANGES IN SEWAGE POLLUTION ON SOFT-BOTIOM MACROFAUNA COMMUNITIES IN THE INNER... more Page 1. EFFECTS OF CHANGES IN SEWAGE POLLUTION ON SOFT-BOTIOM MACROFAUNA COMMUNITIES IN THE INNER OSLOFJORD, NORWAY ... Effects of changes in sewage pollution on soft-bottom macrofauna communities in the inner Oslofjord, Norway. ...
Annales zoologici fennici, vol. 25, 153-164
Science, 2009
Fine-Tuning Fisheries The past decade has seen a tremendous increase in our understanding of how ... more Fine-Tuning Fisheries The past decade has seen a tremendous increase in our understanding of how climate anomalies affect hydrographic properties in North Atlantic Shelf ecosystems, but less about how these events impact organisms. Koeller et al. (p. 791 , see the Perspective by Greene et al. ) measured the egg incubation and hatching times of an important fisheries resource, the pink North Atlantic shrimp, at a variety of locations and compared them to the timing of the local spring phytoplankton bloom. Shrimp reproduction was determined locally by bottom-water temperatures and was not directly coupled with the spring bloom. While the local bottom temperatures and bloom timing are well-matched in general, and match egg hatching to food availability, this evolved relationship can be decoupled by interannual variability and climate change.
Journal of Experimental Marine Biology and Ecology, 1993
As part of a programme to reassess the existence of latitudinal gradients in the diversity of the... more As part of a programme to reassess the existence of latitudinal gradients in the diversity of the macrobenthic infauna of soft sediments, samples were taken from Sassenfjord, Spitzbergen. Abundancebiomass curves showed the shallowest sites to be moderately disturbed, possibly as a result of glacial runoff from the Gipselva. These clearly differed from a site at 123 m which appeared to be in an undisturbed state. A comparison of the diversity profile of the latter site (78"N) with those of physically similar sitca in the North Sea (55 D N) and off the coast of Java (7'S), sampled by identical methods, shows no real difference in diversity.
Environmental and Resource Economics, 2004
A bioeconomic model on the management of by-catch of juvenile fish in the shrimp fishery in the B... more A bioeconomic model on the management of by-catch of juvenile fish in the shrimp fishery in the Barents Sea and the Svalbard Zone, presented by the Norwegian Directorate of Fisheries to the Joint Norwegian Russian Fisheries Commission in 1993, is evaluated. The model is based on management of by-catch through closure of areas when the by-catch of juvenile fish from commercially important species exceeds a critical number. It is argued that although the model may prove useful in bringing economic rationale into the management of by-catch, care must be taken when stocks are in poor shape. This is illustrated by using the high mortality rates and low stock levels experienced for cod and haddock in 2000, and which is expected for the next couple of years. It is therefore discussed when it is appropriate to use the model with reference to the Code of Conduct provided by FAO in 1995.
Deep Sea Research Part II: Topical Studies in Oceanography, 2009
The Jan Mayen area has an extreme environment with low temperatures and infrequent, but abrupt te... more The Jan Mayen area has an extreme environment with low temperatures and infrequent, but abrupt temperature changes. The shrimp population here is considered to be on its edge of distribution. The life-history parameters are in the same range as in other high-latitude shrimp populations and are characterized by slow growth, large size at maturation and extended longevity. Irregular and sporadic
Aquatic Living Resources, 2000
In order to elucidate the population structure of the deep-sea shrimp (Pandalus borealis) in the ... more In order to elucidate the population structure of the deep-sea shrimp (Pandalus borealis) in the NE Atlantic, 32 subsamples and 3 865 individuals were analysed for allozymic variation. They were caught at various locations in the Barents Sea, in waters off Svalbard, Jan Mayen and Iceland, and in fjords along the Norwegian coast. Only three enzymes (malate dehydrogenase, phosphoglucomutase and glucosephosphate isomerase) of the 22 initially tested showed a combination of gel images that could be interpreted with confidence and allozymic variation. The locus coding for malate dehydrogenase was by far the most polymorphic. Samples caught within the Barents Sea and in the Svalbard area showed no significant heterogeneity in allele frequencies, supporting earlier suggestions of only one population of P. borealis in the Barents Sea. Genetic differentiation was found, however, between Norwegian fjords and the Barents Sea, and among fjords.
Zenodo (CERN European Organization for Nuclear Research), Nov 9, 2021
12 s., 2009
A spatio-temporal analysis of Barents Sea survey data from the deeper parts of the Barents Sea sh... more A spatio-temporal analysis of Barents Sea survey data from the deeper parts of the Barents Sea shows a sudden change in fish community structure and abundance taking place in the mid 1980s and 1990s. The change in fish community structure is concomitant with climatic change and increasing fishing effort. Fishery may amplify the effects of climate forcing, and oppose recovery from the impact of climatic events. To characterize the effects of climate and fishery, survey trawl data, temperature data and log book data from the shrimp fishery are analyzed for the period 1980-2007. The climate regime shifts in the mid 80s and 90s with decline in North Atlantic Oscillation and temperature resulted in abrupt decline in fish abundance, decline in biodiversity and increase in pelagic demersal ratio. The shrimp stock also declined and the response of the shrimp industry was a reduction in effort. As the standardised fishing effort is our only measure of fishing impact it becomes difficult to separate between the two impact factors temperature and fisheries. Yet, preliminary results indicate that the shrimp fishery has minor influence on the fish community. The fish community in the Barents Sea has changed into a more North Sea like pelagic-dominated ecosystem. The sudden changes in abundance and diversity reveal that the Barents Sea fish community is sensitive to environmental change. High precaution is needed in the management of all human activities in the Barents Sea due to its low species diversity and resilience.
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Papers by Michaela Aschan