Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 129-131). Also available via the Internet.

The master's thesis focuses on Slapy valley reservoir which is first described as a suitable location for fishing and recreation. Special attention is also paid to its history. The main body of the thesis features the enumeration and characteristics of individual fish species which occur in the reservoir. Furthermore, the thesis deals with the evaluation of the fishing management of the reservoir from 1962 to 2016 considering fish stock and catches of individual species. Factors influencing the development and dynamics of the fish stock are also evaluated. The summary management of Slapy valley reservoir is analyzed in terms of fish stocking and fishing yields. In addition, the population dynamics trends of predatory and non-predatory fish species are analyzed on the basis of fishing catches. In the conclusion, the current condition of the fish stock is evaluated and some minor recommendations for optimizing the fishing management of the reservoir are proposed. KEYWORDS: fish, Slapy, valley reservoir, sport fishing, catch, fish stock, fishing management

Ongoing urbanization and the demand for food, water and recreation influence the sustainability of blue urban spaces. Fishery is a prominent use of urban blue space and can cause pressure on urban nature, its water bodies and fish. This growing pressure requires more attention to how urban dwellers use and value this space and requests smart fishing management for urban areas. To improve knowledge on how to realise sustainable urban fishing, this thesis used an interview study in the city of Hamburg in Germany. Six fishers, two representatives of fishing clubs and one representative of the fishing club association, were interviewed, and the results were combined with observations during one and a half weeks of field study and literature review. The study shows that Germany uses a distinctive approach regarding fishing management with a general ban on catch-and-release and strict regulations. Since fishing law is a state law, the federal state of Hamburg is responsible for its fishing management. The main managing tool is the new fishing law from 2019, developed with scientists and stakeholders to improve fishing in an ethical and sustainable way. The stakeholder’s different impacts on and interests in the rivers of Hamburg have to be respected and are shown in this thesis. The study concludes that management practices have to be managed adaptive to consider changing environmental conditions. Generic fishing management practices (e.g., education of fishers) are limited, while most have to be individually adapted for the environment and fishing culture (e.g., fish protection).

L’objectif de cette thèse est d’améliorer la compréhension du fonctionnement et de la structure trophique du golfe de Gabès en Tunisie. Afin de concilier exigences écologiques et exploitation des ressources marines, différents modèles écosystémiques ont été développés pour étudier sa dynamique trophique et contribuer à la réflexion sur la mise en place de plans de gestion. Un modèle trophique d’équilibre de masse « Ecospace » a été construit afin d’évaluer les conséquences écosystémiques de différentes mesures de gestion. Les résultats des simulations ont permis d’explorer les interactions entre la pêche côtière et la pêche au chalut benthique et d’identifier des zones où les mesures de gestion sont effectives. Un modèle end-to-end a également été appliqué pour expliciter la dynamique des espèces considérées, depuis le forçage climatique jusqu'à la pêche. Cette approche de modélisation consiste à forcer le modèle individu-centré « OSMOSE » par un modèle biogéochimique « Eco3MMed ». Ce modèle a permis d’établir une représentation cohérente du réseau trophique et de simuler des scénarios de gestion théoriques de mise en réserve. Le modèle end-to-end a également été utilisé pour étudier la sensibilité d’un ensemble d’indicateurs écologiques à la pression de pêche. Les résultats ont révélé que les indicateurs de taille sont les plus adaptés pour faire le suivi de l’impact de la pêche dans le golfe de Gabès. Au final, une approche comparative entre plusieurs écosystèmes méditerranéens a été mise en place avec le modèle EcoTroph pour comparer leurs structures trophiques et explorer les effets de plusieurs niveaux d’exploitation par l’analyse de leurs spectres trophiques. / The objective of this thesis is to improve the understanding of trophic structure and functioning of the gulf of Gabes in Tunisia. In order to reconcile environmental concerns and exploitation of marine resources, different ecosystem models have been developed to study the ecosystem dynamics and contribute to the discussion on the implementation of management plans. A spatial and temporal dynamic model “Ecospace” was built to evaluate the ecosystem consequences of different management measures based on scenarios derived from the current regulation. The results of simulations allowed to investigate the interactions between coastal and benthic trawl fishing and to identify areas where management measures are effective. An end-to-end model has been applied to the gulf of Gabes ecosystem to represent the dynamics of 11 high trophic level species, from climate forcing to fishing.This modelling approach consists in forcing the individual-based model "OSMOSE" by a biogeochemical model "ECO3M-Med". This model allowed to establish a coherent representation of the food web and simulate theoretical management scenarios of spatial fishing closure. The end-to-end model has also been used to study the sensitivity of a set of ecological indicators to fishing pressure. The simulation of different levels of fishing mortality showed that size indicators were the most relevant to monitor the impact of fishing in the gulf of Gabes. Finally, a comparative approach between several Mediterranean ecosystems was applied using the EcoTroph model to compare their trophic structures and explore the effects of different levels of fishing pressure through the analysis of their trophic spectra.