Mortality Estimation

Mortality is an essential parameter in understanding the dynamics of any population and sharks are no exception. Without knowledge of how fast individuals are removed from a population it is impossible to model the population dynamics or estimate sustainable rates of exploitation or other useful management parameters.https://scholarworks.wm.edu/vimsbooks/1024/thumbnail.jp

Comparative population genomics of manta rays has global implications for management

Understanding population connectivity and genetic diversity is of fundamental importance to conservation. However, in globally threatened marine megafauna, challenges remain due to their elusive nature and wide-ranging distributions. As overexploitation continues to threaten biodiversity across the globe, such knowledge gaps compromise both the suitability and effectiveness of management actions. Here, we use a comparative framework to investigate genetic differentiation and diversity of manta rays, one of the most iconic yet vulnerable groups of elasmobranchs on the planet. Despite their recent divergence, we show how oceanic manta rays (Mobula birostris) display significantly higher heterozygosity than reef manta rays (Mobula alfredi) and that M. birostris populations display higher connectivity worldwide. Through inferring modes of colonisation, we reveal how both contemporary and historical forces have likely influenced these patterns, with important implications for population management. Our findings highlight the potential for fisheries to disrupt population dynamics at both local and global scales and therefore have direct relevance for international conservation of marine species

Phylogenomics and species delimitation for effective conservation of manta and devil rays

Practical biodiversity conservation relies on delineation of biologically meaningful units. Manta and devil rays (Mobulidae) are threatened worldwide, yet morphological similarities and a succession of recent taxonomic changes impede the development of an effective conservation strategy. Here, we generate genome‐wide single nucleotide polymorphism (SNP) data from a geographically and taxonomically representative set of manta and devil ray samples to reconstruct phylogenetic relationships and evaluate species boundaries under the general lineage concept. We show that nominal species units supported by alternative data sources constitute independently evolving lineages, and find robust evidence for a putative new species of manta ray in the Gulf of Mexico. Additionally, we uncover substantial incomplete lineage sorting indicating that rapid speciation together with standing variation in ancestral populations has driven phylogenetic uncertainty within Mobulidae. Finally, we detect cryptic diversity in geographically distinct populations, demonstrating that management below the species level may be warranted in certain species. Overall, our study provides a framework for molecular genetic species delimitation that is relevant to wide‐ranging taxa of conservation concern, and highlights the potential for genomic data to support effective management, conservation and law enforcement strategies

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Elasmobranch fisheries: status, assessment and management

An overview of the situation of elasmobranch fisheries around the world and problems for their assessment and management are presented. Four different studies are carried out, each attacking a particular problem under this general topic. The first, is an in-depth review of recent trends in elasmobranch exploitation and management on a worldwide basis aimed at closing the gap in baseline information about these fisheries on a global scale. In the second study, a deterministic age-structured simulation model is developed to analyse density-dependent changes in fecundity as a response to increased fishing mortality in a hypothetical shark population. The use of the model as an aid in management decision-making is exemplified with a case from a tropical shark fishery. Monte Carlo analysis is used in the third study, to evaluate the Schaefer and Fox surplus production models and the delay-difference model of Deriso-Schnute for the estimation of assessment and management parameters of elasmobranch fisheries. The fishery models are evaluated by comparing their estimates of stock assessment a n d management parameters against the known values of a full age-structured stochastic simulation model of a shark population. Different scenarios of stock recruitment relationship, fishable stock size, spatial behaviour of the sharks, and data quality are used for testing robustness. None of the fishery models performs satisfactorily under situations of density-dependent catchability. When catchability remains constant, the Deriso-Schnute model outperforms the Schaefer or Fox models, both for biomass and management parameter estimation. In the final study, the multispecies shark fishery of Yucatan, Mexico, is used as an example of the problems for elasmobranch stock assessment in the real world. The fishery is analysed by fitting the Schaefer model to catch and cpue data. The results highlight severe deficiencies in the data available for assessment which are characterised by a lack o f contrast in the cpue data. Some alternative management recommendations aimed at improving the data for assessment are given.Science, Faculty ofResources, Environment and Sustainability (IRES), Institute forGraduat

Fisheries Centre research reports, Vol. 6, no. 6

DIRECTOR'S FOREWORD -- ABSTRACT -- TABLE OF CONTENTS -- LIST OF EXHIBITS -- ACRONYMS AND ABBREVIATIONS -- 1. INTRODUCTION (Ramon Bonfil et al.) • Project Direction and Management -- 2. METHODOLOGY (Ramon Bonfil et al.) -- • Overall Strategy -- • Ecological and Economic Modelling -- • Rapid Appraisal of Fisheries Sustainability -- 3. A GLOBAL OVERVIEW -- • Fishing Patterns of DWFs 1950-1994 (RamonBonfil) -- • Selected Case Studies of DWFs (Ramon Bonfil) -- • Case Study: DWFs off Mauritania and Senegal (Ramon Bonfil) -- • Ecosystem -- • The DWF Nations -- • The Fishery Resources and Fishing Sectors -- • Historical Catches -- • Catches of the DWF -- • Fleet Characteristics and Numbers -- • Fisheries Management by Coastal States -- • Bycatch -- • Fishing Agreements -- • Benefits -- • Conflicts -- • Boxed Case Study 1. Illegal Fishing in the Galapagos Islands {Ramon Bonfil et al.) -- • Case Study: Walleye Pollock and the North Pacific "Donut Hole" (Ramon Bonfil) -- • Ecosystem -- • The DWF Nations -- • The Fishery Resources -- • Historical Catches -- • Fleet Characteristics and Numbers -- • Fisheries Management -- • Bycatch -- • Fishing Agreements -- • Benefits -- • Conflicts --Fisheries Centre (FC)UnreviewedFacultyResearcherPostdoctoralGraduat