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  • 1
    Publication Date: 2015-01-20
    Description: Natural resource managers aim to manage fish stocks at sustainable levels. Often, management of these stocks is based on the results of analytical stock assessments. Accurate catch data, which can be attributed to a specific population unit and reflects the population structure, are needed for these approaches. Often though, the quality of the catch data is compromised when dealing with a complex population structure where fish of different population units mix in a fishery. The herring population units west of the British Isles are prone to mixing. Here, the inability to perfectly allocate the fish caught to the population unit they originate from, due to classification problems, poses problems for management. These mixing proportions are often unknown; therefore, we use simulation modelling combined with management strategy evaluation to evaluate the role fisheries-independent surveys can play in an assessment to provide unbiased results, irrespective of population unit mixing and classification success. We show that failure to account for mixing is one of the major drivers of biased estimates of population abundance, affecting biomass reference points and MSY targets. When mixing of population units occurs, the role a survey can play to provide unbiased assessment results is limited. Either different assessment models should be employed or stock status should be considered from the survey data alone. In addition, correctly classifying the origin of fish is especially important for those population units that are markedly smaller in size than other units in the population complex. Without high classification success rates, smaller population units are extremely vulnerable to overexploitation.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 2
  • 3
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
    Publication Date: 2018-01-22
    Description: The distribution of herring larvae in relation to environmental conditions and the occurrence of possible prey and predator organisms was studied during a 4-day period on a permanent station in the northern North Sea in September 1999. The vertical distribution of herring larvae was sampled in 20-m intervals by means of a multiple-closing net. To resolve the small-scale patchiness of herring larvae and planktonic prey and predator organisms, a towed in-situ video system was used, the Ichthyoplankton Recorder. A diel vertical migration of herring larvae was observed with different intensities depending on their body length. Small larvae (〈10 mm) were concentrated in the upper water layers during daytime and were distributed more homogenously during night time. Large larvae (〉16 mm) showed the highest abundances in the upper water layers during the day and were concentrated in deeper water layers during the night. The presented results appear to be relevant for individual-based modelling of the fate of larval herring populations. La distribución a pequeña escala y la migración vertical de larvas de arenque del Mar del Norte (Clupea harengus, Teleostei: Clupeidea) en relación con factores abióticos y bióticos. – Se han estudiado la distribución de las larvas de arenque en relación a las condiciones ambientales y la incidencia de posibles presas y organismos depredadores a lo largo de un periodo de 4 días en una estación permanente situada en el Mar del Norte en septiembre de 1999. La distribución vertical de las larvas de arenque fue muestreada en intervalos de 20 m mediante una red de apertura múltiple (multiple opening/closing net). Para determinar a pequeña escala la heterogeneidad en la distribución de las larvas de arenque, así como de las presas y depredadores planctónicos, se utilizó un sistema de vídeo in-situ (The Ichthyoplankton Recorder). Se observó una migración vertical nictimeral con diferentes intensidades dependiendo de la longitud corporal de las larvas. Las larvas pequeñas (〈10 mm) se concentraban en las capas superiores de la columna de agua durante el día y se distribuían más homogéneamente durante la noche. Las larvas más grandes (〉16 mm) mostraban su mayor abundancia en las capas superiores de la columna de agua durante el día y se concentraban en capas de agua más profundas durante la noche. Los resultados presentados en este trabajo pueden ser relevantes para la modelización (individual based modeling) del destino de las poblaciones de larvas del arenque.
    Type: Article , PeerReviewed
    Format: text
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