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  • 1
    In: Marine Biology Research, Informa UK Limited, Vol. 8, No. 5-6 ( 2012-06-01), p. 415-419
    Type of Medium: Online Resource
    ISSN: 1745-1000 , 1745-1019
    Language: English
    Publisher: Informa UK Limited
    Publication Date: 2012
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  • 2
    Online Resource
    Online Resource
    Editorial CSIC ; 2003
    In:  Scientia Marina Vol. 67, No. S1 ( 2003-04-30), p. 325-335
    In: Scientia Marina, Editorial CSIC, Vol. 67, No. S1 ( 2003-04-30), p. 325-335
    Type of Medium: Online Resource
    ISSN: 1886-8134 , 0214-8358
    Uniform Title: Forecasting recruitment and stock biomass of Northeast Arctic cod using neural networks
    URL: Issue
    Language: English , English
    Publisher: Editorial CSIC
    Publication Date: 2003
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  • 3
    In: Fish and Fisheries, Wiley, Vol. 17, No. 1 ( 2016-03), p. 165-175
    Abstract: Fish stock productivity, and thereby sensitivity to harvesting, depends on physical (e.g. ocean climate) and biological (e.g. prey availability, competition and predation) processes in the ecosystem. The combined impacts of such ecosystem processes and fisheries have lead to stock collapses across the world. While traditional fisheries management focuses on harvest rates and stock biomass, incorporating the impacts of such ecosystem processes are one of the main pillars of the ecosystem approach to fisheries management ( EAFM ). Although EAFM has been formally adopted widely since the 1990s, little is currently known to what extent ecosystem drivers of fish stock productivity are actually implemented in fisheries management. Based on worldwide review of more than 1200 marine fish stocks, we found that such ecosystem drivers were implemented in the tactical management of only 24 stocks. Most of these cases were in the North Atlantic and north‐east Pacific, where the scientific support is strong. However, the diversity of ecosystem drivers implemented, and in the approaches taken, suggests that implementation is largely a bottom‐up process driven by a few dedicated experts. Our results demonstrate that tactical fisheries management is still predominantly single‐species oriented taking little account of ecosystem processes, implicitly ignoring that fish stock production is dependent on the physical and biological conditions of the ecosystem. Thus, while the ecosystem approach is highlighted in policy, key aspects of it tend yet not to be implemented in actual fisheries management.
    Type of Medium: Online Resource
    ISSN: 1467-2960 , 1467-2979
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
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  • 4
    In: Fish and Fisheries, Wiley, Vol. 24, No. 2 ( 2023-03), p. 297-320
    Abstract: The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ecology, of three spatially distant populations (stocks) of Atlantic cod ( Gadus morhua , Gadidae) (50–80° N), in the Irish/Celtic Seas‐English Channel Complex, North and Barents Seas, under past and projected climate. First, experimental tracking of spawning behaviour evidenced that the ovulation cycle is highly distressed at ≥9.6 (±0.25)°C ( T up ). This knife‐edge threshold resulted in erratic spawning frequencies, whereas vitellogenin sequestration remained unaffected, indicating endocrine rather than aerobic scope constraints. Cod in the Celtic Sea‐English Channel are, therefore, expected to show critical stock depensation over the next decades as spawning grounds warm above T up , with Irish Sea cod subsequently at risk. Second, in the relatively cooler North Sea, the northward retraction of Calanus finmarchicus (Calanidae) and Para‐Pseudocalanus spp. (Clausocalanidae) (1958–2017) limit cod larvae feeding opportunities, particularly in the southernmost subarea. However, the contrasting increase in Calanus helgolandicus (Calanidae) does not counteract this negative effect, likely because cod larvae hatch ahead of its abundance peaks. Overfishing again comes as a twin effect. Third, in the still relatively cold Barents Sea, the sustainably harvested cod benefit from improved food conditions in the recent ice‐free polar region but at the energetic cost of lengthier and faster spawning migrations. Consequently, under climate change local stocks are stressed by different mechanistic factors of varying management severity.
    Type of Medium: Online Resource
    ISSN: 1467-2960 , 1467-2979
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2023
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  • 5
    Online Resource
    Online Resource
    Oxford University Press (OUP) ; 2004
    In:  ICES Journal of Marine Science Vol. 61, No. 7 ( 2004-01-01), p. 1201-1213
    In: ICES Journal of Marine Science, Oxford University Press (OUP), Vol. 61, No. 7 ( 2004-01-01), p. 1201-1213
    Abstract: The objective of this study was to use spatially explicit individual-based models for simulating the movement, foraging, growth, and mortality of cod and capelin in the Barents Sea in order to identify general features in their migration patterns and the consumption of capelin by cod. The individual-based models are initiated from survey data run over 1 year and validated against survey information. Directed movement is based on a combination of movement vectors and temperature boundaries, and bioenergetics models are used to calculate growth. Capelin consumption by cod is calculated from local encounters between the species. For capelin, the best movement model can be summarized as: stay southwest of the 2.5°C and 4°C temperature front at 50-m depth for juvenile and mature individuals, respectively, in winter, and migrate northwards during summer, but do not pass the −1.5°C temperature front. The best cod model was to migrate south-southwest during winter and north-northeast during summer, within the temperature range 1°C to 8°C. The annual consumption estimates found here reflected the interannual and seasonal pattern from previous studies based on stomach samples, but were generally lower. Consumption estimates varied depending on the movement models, and the best movement model also produced the consumption estimate closest to that obtained in other studies. Introducing a simple rule stating that cod should move in a randomly selected direction when the local capelin density is zero increased the consumption estimate by 30%. This suggests that more emphasis needs to be put on exploring how behavioural rules in predators and prey affect their interactions. Even though there are some discrepancies between predictions and observations, the results achieved by the model with regard to spatial distribution, growth, and consumption are promising.
    Type of Medium: Online Resource
    ISSN: 1095-9289 , 1054-3139
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2004
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  • 6
    Online Resource
    Online Resource
    Elsevier BV ; 2010
    In:  Journal of Marine Systems Vol. 79, No. 3-4 ( 2010-2), p. 343-360
    In: Journal of Marine Systems, Elsevier BV, Vol. 79, No. 3-4 ( 2010-2), p. 343-360
    Type of Medium: Online Resource
    ISSN: 0924-7963
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2010
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    detail.hit.zdb_id: 1041191-4
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  • 7
    In: Marine Biology Research, Informa UK Limited, Vol. 8, No. 5-6 ( 2012-06-01), p. 420-441
    Type of Medium: Online Resource
    ISSN: 1745-1000 , 1745-1019
    Language: English
    Publisher: Informa UK Limited
    Publication Date: 2012
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    detail.hit.zdb_id: 2168764-X
    SSG: 12
    SSG: 21,3
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  • 8
    Online Resource
    Online Resource
    Canadian Science Publishing ; 2016
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 73, No. 2 ( 2016-02), p. 177-188
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 73, No. 2 ( 2016-02), p. 177-188
    Abstract: Johan Hjort’s so-called second recruitment hypothesis addressed the fate of offspring that drift out of areas suitable for their survival. This hypothesis has forged the concept of a population as a closed life cycle, making countercurrent adult spawning migration a necessary mechanism in balancing larval drift. The Norwegian spring-spawning (NSS) herring stock (Clupea harengus), the object of much of Hjort’s work, is spread over large areas in the Northeast Atlantic, with spawning along the Norwegian coast, nursery areas in the Barents Sea, feeding areas in the Norwegian Sea, and overwintering areas outside northern Norway. Understanding the spatial dynamics of highly migratory fish stocks such as the NSS herring, therefore, is critical to understanding their population dynamics. Here I review hypotheses on the spatial dynamics of fish focusing on NSS herring and discuss consequences for population dynamics and interactions with other ecosystem components. The results illustrate the key role that strong herring cohorts play both as predators in the Barents and Norwegian seas and as prey on the overwintering and spawning grounds along the Norwegian coast. It is advocated that spatial full life cycle models should be developed for key fish stocks as a meeting place for model assumptions and observations and as a test bed for a multiple hypothesis testing approach.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2016
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    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
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  • 9
    Online Resource
    Online Resource
    Canadian Science Publishing ; 1999
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 56, No. S1 ( 1999-11-30), p. 26-34
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 56, No. S1 ( 1999-11-30), p. 26-34
    Abstract: We evaluated the costs and benefits of long-distance horizontal migration by pelagic planktivores, Atlantic herring (Clupea harengus), blue whiting (Micromesistius poutassou), mackerel (Scomber scombrus), and capelin (Mallotus villosus) in the Norwegian and Barents seas using a numerical model and tested model predictions against field observations. Specifically, we considered (i) energetic costs as a function of body size, water currents, swimming speed, and distance, (ii) time costs as a function of speed and distance, and (iii) energetic gain in terms of differences in food intake between areas. The model demonstrates how body size restricts large-scale horizontal migration patterns. Model and field results suggest that the extent of migration will increase with increasing body length. The model predicts that long-distance migration costs may exceed energy intake for fish 〈 20 cm, due to increased hydrodynamical drag with decreasing fish size. Field results suggest that migration distance is a function of length, weight, and age. Food abundance and distribution, current speed and direction, and differences in day length at boreal latitudes are believed to be the major driving forces influencing large-scale migration distance, direction, and timing in pelagic planktivores. Northwards latitudinal rather than longitudinal feeding migrations are explained by the improved feeding opportunities with increased day lengths.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 1999
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  • 10
    Online Resource
    Online Resource
    Canadian Science Publishing ; 2007
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 64, No. 12 ( 2007-12-01), p. 1747-1760
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 64, No. 12 ( 2007-12-01), p. 1747-1760
    Abstract: We investigate the trade-offs associated with vertical migration and swimming speed of Atlantic cod (Gadus morhua) using an adaptive individual-based model. Simulations with varying distribution and occurrence of prey, with and without swimbladder constraints, and visual predation were performed. Most simulations resulted in cod migrations between the bottom and pelagic zones. In simulations with high probability of encountering pelagic prey, the cod spent the daytime in the pelagic zone, moving to the bottom to feed only when no pelagic prey were encountered. At night the cod stayed in the pelagic zone to attain neutral buoyancy. In simulations with low occurrence of pelagic prey or high visual predation pressure, the cod remained at the bottom feeding on the consistently present benthic prey. If the pelagic prey occurred far above the sea floor or there were no benthic prey, the cod abandoned all bottom contact. The study thus predicts that the probability of encountering energy-rich pelagic prey is the key factor in driving vertical migration in adult cod. Buoyancy regulation is further shown to be an important constraint on vertical migration.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2007
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    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
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