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URI [dataset] UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES School of Ocean and Earth Science THE TROPHO-SPATIAL ECOLOGY OF DEEP-SEA SHARKS AND CHIMAERAS FROM A STABLE ISOTOPE PERSPECTIVE by Christopher S. Bird A thesis submitted to the University of Southampton in accordance with the requirements for the degree of Doctor of Philosophy November 2017 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES School of Ocean and Earth Science Doctor of Philosophy THE TROPHO-SPATIAL ECOLOGY OF DEEP-SEA SHARKS AND CHIMAERAS FROM A STABLE ISOTOPE PERSPECTIVE Christopher Stephen Bird Chondrichthyans (sharks, rays and chimaera) are one of the most speciose groups of higher order predators on the planet and are often cited as playing an important functional role in many ecosystems. However, most studies to date have focused on oceanic and shelf habitats, and there is limited information on the ecological role that chondrichthyans play in the deep-sea. This research aims to examine the trophic and spatial ecology of deep-sea chondrichthyans using stable isotope analysis. Stable isotopes of carbon and nitrogen vary among different trophic levels and between spatially separated areas, and therefore provide a potential tool for uncovering some ecological characteristics of deep-water chondrichthyans. In this study, I found that on a global scale, oceanic sharks appear to transfer nutrients over large spatial scales, whereas sharks found in shelf habitats couple ecologically varied food webs close to their capture location. Although global data is limited for deep-sea sharks, in the northeast Atlantic it appears that sharks found on seamounts are more tightly coupled to pelagic production than their counterparts on the continental slopes. Continental slope habitats may provide access to more isotopic niches, where sharks integrate nutrients from benthic and pelagic nutrient pathways. On the other hand, chimaeras appear to fill a unique role feeding on benthic prey items that are inaccessible to other fishes (e.g hard shelled benthic animals). Depth gradients in nutrient availability are reflected in the bathymetric distribution patterns of chondrichthyan families, with depth segregations likely reducing interspecific competition for resources. For some of the largest shark species in this ecosystem, such as Portuguese dogfish (Centroscymnus coelolepis) and leafscale gulper shark (Centrophorus squamosus), whole life-history ecology was recovered from sequential analysis of eye lens proteins. Both these species appear to undertake relatively consistent latitudinal migrations linked with ontogeny and reproductive development. This study reveals the ecological characteristic of diverse deep-sea chondrichthyan assemblages, and how trophic and spatial behaviours facilitate the transfer of nutrients in these ecosystems. Subsequently, chondrichthyans likely play an important role in deep-sea ecosystems and should be managed appropriately within fisheries. Table of Contents Table of Contents ............................................................................................................................... i List of Tables ..................................................................................................................................... v List of Figures .................................................................................................................................. vii Declaration of Authorship ............................................................................................................... xi Acknowledgements ......................................................................................................................... xiii Chapter 1: Thesis Introduction ............................................................................................ 1 1.1 Deep-sea Chondrichthyans ................................................................................................... 3 1.1.1 Evolutionary Ecology ................................................................................................ 3 1.2 Deep-sea Environments ........................................................................................................ 5 1.2.1 Nutrient Dynamics ..................................................................................................... 6 1.3 Stable Isotope Ecology ......................................................................................................... 8 1.3.1 Trophic Ecology ........................................................................................................ 8 1.3.2 Spatial Ecology ........................................................................................................ 10 1.3.3 Depth Gradients ....................................................................................................... 11 1.3.4 Stable Isotopic Applications in the Study of Shark Ecology ................................... 11 1.3.5 Lipid and Urea Contaminations ............................................................................... 12 1.4 Deep-water Chondrichthyan Ecology ................................................................................ 14 1.4.1 Fisheries Vulnerability ............................................................................................. 16 1.5 Thesis Aims and Objectives ............................................................................................... 17 1.6 Thesis Structure .................................................................................................................. 18 Chapter 2: A global perspective on the trophic geography of sharks ............................ 21 2.1 Abstract ............................................................................................................................... 21 2.2 Introduction ........................................................................................................................ 22 2.3 Results ................................................................................................................................ 24 2.4 Discussion ........................................................................................................................... 26 2.5 Concluding Remarks .......................................................................................................... 32 2.6 Methods .............................................................................................................................. 33 2.6.1 δ13C Baseline Predictions ........................................................................................ 34 2.6.2 Mathematical Models .............................................................................................. 35 2.7 Supplementary Information ................................................................................................ 36 13 13 2.7.1 Linking the δ C values of sharks to simulated δ C values of phytoplankton ........ 36 i 2.7.2 Interpretation of Shelf Variation .............................................................................. 38 Chapter 3: Mesopredatory deep-sea sharks reveal differences in food web structure between seamounts and continental slopes across the northeast Atlantic. .............. 41 3.1 Abstract .............................................................................................................................. 41 3.2 Introduction ........................................................................................................................ 41 3.3 Materials and Methods ....................................................................................................... 44 3.3.1 Sampling .................................................................................................................. 44 3.3.2 Stable Isotope Analysis ........................................................................................... 46 3.3.3 Data Analysis ........................................................................................................... 47 3.4 Results ................................................................................................................................ 47 3.5 Discussion .......................................................................................................................... 52 Chapter 4: Ecological characteristics of sharks and chimaeras in continental slope ecosystems .....................................................................................................................