The monitoring of the spatiotemporal distribution and movement of brown shrimp (Crangon crangon L.) using commercial and scientific research data Dissertation with the aim of achieving a doctoral degree at the Faculty of Mathematics, Informatics and Natural Sciences Department of Biology of University of Hamburg submitted by Katharina Schulte 2015 in Hamburg The following evaluators recommend the admission of the dissertation: Prof. Dr. Axel Temming Jun. Prof. Dr. Marc Hufnagl Date of Disputation: 02nd June 2016 TABLE OF CONTENTS 1 SUMMARY............................................................................................................................. 2 2 ZUSAMMENFASSUNG ...................................................................................................... 7 3 OUTLINE OF PUBLICATIONS ....................................................................................... 13 3.1 Manuscript 1 ..........................................................................................................................13 3.2 Manuscript 2 ..........................................................................................................................13 3.3 Manuscript 3 ..........................................................................................................................13 4 GENERAL INTRODUCTION .......................................................................................... 14 4.1 Beam trawl survey data ........................................................................................................20 4.2 Vertically resolving stow net data.......................................................................................20 4.3 Commercial data ...................................................................................................................21 4.4 Thesis objectives ....................................................................................................................22 4.5 References ...............................................................................................................................23 5 MANUSCRIPT 1 ................................................................................................................. 30 5.1 Abstract ...................................................................................................................................31 5.2 Introduction ...........................................................................................................................32 5.3 Material and Methods...........................................................................................................34 5.4 Results .....................................................................................................................................41 5.5 Discussion...............................................................................................................................50 5.6 Conclusion ..............................................................................................................................55 5.7 Acknowledgements ..............................................................................................................56 5.8 References ...............................................................................................................................56 6 MANUSCRIPT 2 ................................................................................................................. 62 6.1 Abstract ...................................................................................................................................63 6.2 Introduction ...........................................................................................................................64 6.3 Material and Methods...........................................................................................................68 6.4 Results .....................................................................................................................................76 6.5 Discussion...............................................................................................................................86 6.6 Conclusion ..............................................................................................................................89 6.7 Acknowledgements ..............................................................................................................90 6.8 References ...............................................................................................................................90 7 MANUSCRIPT 3 ................................................................................................................. 95 7.1 Abstract ...................................................................................................................................96 7.2 Introduction ...........................................................................................................................97 7.3 Material & Methods ............................................................................................................100 7.4 Results ...................................................................................................................................106 7.5 Discussion.............................................................................................................................116 7.6 Conclusion ............................................................................................................................121 7.7 Acknowledgements ............................................................................................................122 7.8 References .............................................................................................................................123 Table of contents 1 8 GENERAL DISCUSSION................................................................................................ 128 8.1 Brown shrimp stock assessment and accompanying uncertainties .............................129 8.2 New knowledge on the spatiotemporal distribution of brown shrimp.......................132 8.3 Conclusion ............................................................................................................................138 8.4 References .............................................................................................................................139 9 ACKNOWLEDGEMENTS .............................................................................................. 144 10 DECLARATION ON OATH ........................................................................................... 151 1 SUMMARY This study aimed at closing important knowledge gaps relevant for the stock assessment of brown shrimp (Crangon crangon L.), a species supporting a large fishery with over 500 active vessels, mainly fishing on brown shrimp with annual landings exceeding 30 000 t. The majority of the annual catch is obtained by the Dutch and German fleet mainly operating in Natura 2000 sites of the Wadden Sea, designated for the protection of habitats. Despite the sensitive location of the fishing grounds and the large size of the fleet, the European brown shrimp fishery is currently unmanaged. However, recently a management strategy has been discussed for the brown shrimp stock as well as for the Natura 2000 sites. A management plan for the brown shrimp stock appears to be necessary since there are indications of growth overfishing. A potential risk for the brown shrimp population exists due to the increasing efficiency of the fleet, which is also reflected in increased mean annual landing volumes of 32 972 t (2000 – 2013), which nearly is twice the amount of the mean landing volume of 16 820 t reached from 1960 – 1999. Therefore, the International Council for the Exploration of the Sea (ICES) in October 2014 advised to implement a management of the brown shrimp stock. Due to the short life span of brown shrimp an annual stock assessment based on scientific surveys and the determination of annual total allowable catches (TACs) are not suitable. Consequently, ICES recommends that the management ought to be based on monthly commercial brown shrimp catches including the monitoring of commercial landings per unit effort (LPUE) and an additional scientific monitoring to obtain independent estimates, for example on biomass. Unlike the brown shrimp stock management, the management considerations for the Natura 2000 sites focus on spatial protection measures for specific habitats and can therefore be expected to affect the brown shrimp fishery and in consequence also potentially the brown shrimp stock. The Natura 2000 management considerations include the estimation of the degree of degradation or destruction to which those sites are exposed. In order to protect ecologically coherent areas, the establishment of spatial closures for the brown shrimp fishery is suggested. The suitability and the potential impact of any possible future management option, either for Natura 2000 sites or for the brown shrimp stock can only be discussed if so far unavailable spatiotemporal variations in the brown shrimp abundance are described. Up to now, knowledge on the spatial distribution of brown shrimp is derived from spatially limited annual survey data only. However, commercial data are available, providing information from more than 200 German brown shrimp vessels with