An ecosystem approach to fisheries management: The Atlantic seabob shrimp (Xiphopenaeus kroyeri) in Suriname TOMAS WILLEMS AN ECOSYSTEM APPROACH TO FISHERIES MANAGEMENT: THE ATLANTIC SEABOB SHRIMP (XIPHOPENAEUS KROYERI) IN SURINAME TOMAS WILLEMS Ghent University Faculty of Sciences Biology Department Marine Biology Research Group Institute for Agricultural and Fisheries Ressearch (ILVO) Ankerstraat 1 8400 Oostende Belgium Antom De Kom Universiteit van Suriname Leysweg 86 Paramaribo Suriname Publically defended on 02/06/2016 Picture copyrights Cover: seabob trawler off Suriname © Tomas Willems Pictures invertebrates (Chapter 2) © Jan Ranson/Hans Hillewaert/Tomas Willems Pictures fishes (Chapter 3) © Hans Hillewaert/Tomas Willems Unless specified otherwise, all pictures in this thesis © Tomas Willems Vormgeving [email protected] ISBN 978-9-4619740-1-3 For citation to the published work reprinted in this thesis, please refer to the original publications (as mentioned at the beginning of each chapter). Please cite this thesis as: Willems, T., 2016. An ecosystem approach to fisheries management: the Atlantic seabob shrimp (Xiphopenaeus kroyeri) in Suriname. Ghent University, 310 pp. AN ECOSYSTEM APPROACH TO FISHERIES MANAGEMENT: THE ATLANTIC SEABOB SHRIMP (XIPHOPENAEUS KROYERI) IN SURINAME EEN ECOSYSTEEMBENADERING IN VISSERIJBEHEER: DE ATLANTISCHE SEABOBGARNAAL (XIPHOPENAEUS KROYERI) IN SURINAME TOMAS WILLEMS PROMOTERS Prof. Dr. Magda Vincx Prof. Dr. Marleen De Troch Dr. Kris Hostens Dr. Annelies De Backer Prof. Dr. Jan Mol Academic year 2015 – 2016 Thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Marine Sciences MEMBERS OF THE EXAMINATION COMMITTEE Dr. Jan Reubens - Ghent University & VLIZ, Belgium Dr. Nathalie Steins - IMARES WageningenUR, The Netherlands Prof. Dr. Filip Volckaert - KU Leuven, Belgium CHAIR Prof. Dr. Ann Vanreusel - Ghent University, Belgium SECRETARY Prof. Dr. Tom Moens - Ghent University, Belgium PROMOTERS Prof. Dr. Magda Vincx - Ghent University, Belgium Prof. Dr. Marleen De Troch - Ghent University, Belgium Dr. Kris Hostens - ILVO, Belgium Dr. Annelies De Backer - ILVO, Belgium Prof. Dr. Jan Mol - ADEK University, Suriname TABLE OF CONTENTS Summary 8 Samenvatting 14 Populaire samenvatting 20 List of abbreviations 25 Chapter 1 General introduction 28 Chapter 2 Spatio-temporal distribution patterns of the epibenthic 64 community in the coastal waters of Suriname Chapter 3 Distribution patterns of the demersal fish fauna on the 92 inner continental shelf of Suriname Chapter 4 Trophic ecology of Atlantic seabob shrimp 118 Xiphopenaeus kroyeri: intertidal benthic microalgae support the subtidal food web off Suriname Chapter 5 ‘Wasp-waist’ control in a coastal benthic ecosystem? 144 Atlantic seabob shrimp Xiphopenaeus kroyeri as a key prey species for the demersal fish community off Suriname Chapter 6 Catch composition in seabob shrimp Xiphopenaeus 172 kroyeri trawl fisheries off Suriname Chapter 7 Ray bycatch in a tropical shrimp fishery: do bycatch 200 reduction devices and turtle excluder devices effectively exclude rays? Chapter 8 General discussion: integrating scientific knowledge as a 218 baseline for fisheries management Annexes 245 Cited literature 289 Dankwoord 306 7 ǀ TABLE OF CONTENTS SUMMARY The Ecosystem Approach to Fisheries (EAF) is widely acknowledged as being the best approach to future fisheries management. In contrast to traditional single-species management, an EAF explicitly recognizes the complexity of ecosystems in which fisheries operate. As such, fundamental elements to be considered in an EAF include: (1) the trophic relationships between exploited species and their food sources, (2) indirect interactions between fishing fleets - through trophic linkages or bycatch - and (3) the impact of fishing on marine habitats and species communities. The disregard of these aspects in fisheries management lies at the basis of several environmental and socio-economic problems associated with tropical shrimp trawl fisheries. These fisheries remain the main supplier of shrimp to the global market, but face a negative public perception. The increasing market demand for sustainable seafood products has triggered the fishery for Atlantic seabob shrimp Xiphopenaeus kroyeri (Crustacea: Penaeoidea) off the coast of Suriname to take steps towards more environmentally sustainable fishing practices. This led to the seabob fishery obtaining a Marine Stewardship Council (MSC) ecolabel in 2011, which is already a major step towards the implementation of an EAF. Nevertheless, as highlighted during the MSC assessments, crucial information is lacking to assess the impact of seabob fisheries on certain aspects of the regional ecosystem structure and functioning. This doctoral thesis aimed to provide relevant knowledge needed for an improved ecosystem approach to the management of Xiphopenaeus kroyeri trawl fisheries off Suriname. More specifically, we focused on (1) the characterization of the benthic assemblages and habitats of the inner continental shelf where X. kroyeri fisheries take place (ecosystem structure), (2) the role of X. kroyeri in the coastal food web of Suriname (ecosystem functioning), (3) the impact of X. kroyeri trawling on ecosystem structure and functioning (ecosystem impact) and (4) the translation of the scientific results into recommendations for fisheries management (management implications). Chapter 1 sets the broader scene by introducing the current fisheries crisis, the EAF concept and the MSC ecolabel. Next, the problems and challenges related to shrimp fisheries and more specifically to seabob fisheries in Suriname are outlined. The thesis further constitutes of seven chapters which are organized in four parts, each related to one of the four objectives of this doctoral study. Since ecological research on the Suriname continental shelf has been limited, Chapters 2 and 3 (i.e. PART I) aimed to characterize the demersal assemblages in the coastal waters of Suriname. Therefore, epibenthos, demersal fish and environmental parameters were sampled during an extensive trawl survey in 2012-2013. Data were collected on a (bi)monthly basis at 15 locations in the shallow (<40 m) coastal area. The spatio-temporal distribution of epibenthic 8 ǀ SUMMARY fauna was described in Chapter 2, together with the abiotic characteristics of the inner Suriname Shelf. From 148 trawl samples, 92 epibentic taxa were identified. These occurred in three spatially distinct species assemblages, related to clear gradients in some environmental parameters. A species-poor coastal assemblage, dominated by X. kroyeri, was discerned within the muddy, turbid-water zone (6 to 20 m depth). Close to the 30 m isobath, sediments were much coarser (median grain size on average 345 ± 103 μm vs. 128 ± 53 μm in the coastal assemblage) and water transparency was much higher (on average 7.6 ± 3.5 m vs. 2.4 ± 2.1 m in the coastal assemblage). In this zone, a diverse offshore epibenthic assemblage was found, characterized by brittle stars (mainly Ophioderma brevispina and Ophiolepis elegans) and a variety of crabs, sea stars and hermit crabs. A transition assemblage occurred in between both zones, with epibenthic species typically found in either the coastal or offshore assemblages, but mainly characterized by the absence of X. kroyeri. The demersal fish community of the inner Suriname Shelf (Chapter 3) included 98 species, but trawl samples were dominated by Stellifer rastrifer, Amphiarius rugispinis and Cynoscion jamaicensis, which accounted for 50 % of the catches by number. In analogy with the epibenthic community, cluster analysis revealed three species assemblages in a nearshore-offshore depth gradient. The coastal fish assemblage, occurring in the shallow turbid waters up to 20 m depth, represented the ‘sciaenid community’ of tropical shelves and was dominated by Sciaenidae and Ariidae. Around 27 m water depth, a transition assemblage marked the shift towards a very different offshore fish assemblage on the deepest sampling locations (34 m). The offshore assemblage had a significantly lower demersal fish density and diversity, and contained representatives of fish families typical for deeper tropical shelves, such as Paralichthyidae, Triglidae and Lutjanidae. Although clear seasonal differences were noted in the environmental characteristics (e.g. dry vs. rainy season), little temporal variation was observed in the communities of epibenthos and demersal fish. They were primarily spatially structured, in an on-offshore gradient related to depth, sediment grain size and sediment total organic carbon content. The shift between the coastal and offshore assemblages was the most important feature of the benthic communities of the inner Suriname Shelf, and coincided with a transition between two principal ecosystems: a coastal, river influenced system fueled by detritus versus an open shelf system based on primary production. Demersal fishes thrived in the coastal ecosystem, together with a potentially important epibenthic food source, the seabob shrimp X. kroyeri, which reached very high densities (up to 1383 individuals 1000 m-²). Further, the shallow nearshore waters at less than 20 m depth may have an important nursery function, because juveniles of commercially important demersal fishes were abundant in our coastal trawl catches. The first part of the thesis made clear that X. kroyeri dominates the epibenthic community of the coastal waters (<27 m depth) off Suriname, and that its 9 ǀ