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Het kokkelbestand in de Nederlandse kustwateren in 2019
van Asch, M.; van den Ende, D.; van der Pool, J.; Brummelhuis, E.; van Zweeden, C.; van Es, Y.; Troost, K. (2019). Het kokkelbestand in de Nederlandse kustwateren in 2019. CVO (Centrum voor Visserijonderzoek) Report, 19.009. Stichting Wageningen Research, Centrum voor Visserijonderzoek (CVO): IJmuiden. 28 pp. https://hdl.handle.net/10.18174/497849

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Auteurs  Top | Dataset 
  • van Asch, M., meer
  • van den Ende, D., meer
  • van der Pool, J., meer
  • Brummelhuis, E.
  • van Zweeden, C., meer
  • van Es, Y.
  • Troost, K.

Abstract
    Wageningen Marine Research conducts cockle (Cerastoderma edule) stock assessments in the Dutch coastal waters. This is an annual inventory that takes place by order of the Ministry of Agriculture, Nature and Food Quality (LNV). Wageningen Marine Research started cockle stock assessments in the Dutch part of the Wadden Sea and Oosterschelde bay in 1990 and in the Westerschelde estuary in 1992. Based on these inventories, the Ministry of LNV determines quota permits each year. Furthermore, the survey results are highly relevant for the evaluation of effects of fisheries and nature management, and for impact studies e.g. within the framework of Natura 2000. This report presents the results of the cockle stock inventory carried out in spring 2019 in the intertidal of the Dutch Wadden Sea, Oosterschelde bay and Westerschelde estuary. From this inventory, the expected total cockle stocks, and cockle stock in harvestable densities in September 2019 are predicted by extrapolation based on assumed growth and mortality. In addition to the surveys presented here, cockles are also monitored on a yearly basis in the Voordelta coastal area (since 1993) as well as in the lake Grevelingenmeer and lake Veerse Meer areas (since 2017). The results of those surveys are reported separately (Perdon et al., in prep.; Van der Pool et al., in prep.). In the intertidal areas of the Dutch Wadden Sea the total cockle stock was estimated at 196.4 million kg fresh weight. Calculated biomass in autumn (September 1st) 2019 is 308.1 million kg fresh weight. Of this, 46.2 million kg is cockle flesh (assuming an average flesh weight of 15%). In the Oosterschelde bay total cockle stock in spring 2019 was estimated at 13.8 million kg fresh weight. Calculated biomass in autumn is 23.3 million kg fresh weight. Of this, 3.5 million kg is cockle flesh. In the Westerschelde estuary, the estimated total cockle stock was 6.3 million kg fresh weight. Calculated biomass in autumn 2019 is 10.0 million kg fresh weight. Of this, 1.5 million kg is cockle flesh. The harvestable stock is calculated for the three areas separately as the biomass present at densities of more than 50 cockles per m2. Harvestable stock estimates are 33.8, 1.8 and 1.0 million kg cockle flesh in autumn, for the Wadden Sea, Oosterschelde bay and Westerschelde estuary, respectively. In all three areas most of the cockle biomass is formed by last years’ spatfall. During the summer of 2018 cockle mortality was very high, most likely due to the prolonged heatwave at the time (Troost and Van Asch, 2018). At that time the vast majority of cockles was several years old. Just before the heatwave a large spatfall occurred. These cockles are now 1-year old, and form the majority of the stock this year. Because of this large spatfall, cockle stock in de Wadden Sea is similar to that of the previous spring. In the Oosterschelde bay almost all cockles of 1-year and older died during the summer of 2018, but due to a large spatfall the cockle stock found in spring 2019 was “only” 56% lower than in spring 2018. Cockle stocks in the Westerschelde estuary, though relatively low, more than doubled compared to last year.

Dataset
  • Kokkelbestand Westerschelde, meer

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