Bioressources Aquatiques
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Actes du IXème Congrès Maghrébin des Sciences de la Mer, Sousse 2014 Item Type Book/Monograph/Conference Proceedings Publisher INSTM, Institut national des sciences et technologies de la mer Download date 10/10/2021 09:30:59 Link to Item http://hdl.handle.net/1834/15866 Bulletin de l’Institut National des Sciences de la Mer (INSTM Salammbo). Numéro Spécial (18) : Actes du IXème Congrès Maghrébin des Sciences de la Mer Sousse : 2014 BIORESSOURCES AQUATIQUES: 1 Bulletin de l’Institut National des Sciences de la Mer (INSTM Salammbo). Numéro Spécial (18) : Actes du IXème Congrès Maghrébin des Sciences de la Mer Sousse : 2014 The use of Ecospace model as a simulation tool for fisheries management plans: case of the Gulf of Gabes Abdou K.(1), Halouani G.(2), Hattab T.(3), Ben Rais Lasram F.(4), Romdhane M.S.(5), Le Loc’h F.(6) (1) UR 03AGRO1 Ecosystèmes et Ressources Aquatiques, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Tunis, Tunisie. Email: [email protected]. (2) UMR 6539 LEMAR CNRS/UBO/IRD/IFREMER, Institut Universitaire Européen de la Mer, Technopôle Brest- Iroise, Rue Dumont d'Urville, 29280 Plouzané, France. Email: [email protected] (3) Unité de Recherche Écologie et Dynamique des Systèmes Anthropisés (EDYSAN FRE 3498 CNRS-UPJV), Université de Picardie Jules Verne, Rue des Louvels, 80000 Amiens, France. Email: [email protected] (4) UR 03AGRO1 Ecosystèmes et Ressources Aquatiques, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Tunis, Tunisie. Email: [email protected] (5) UR 03AGRO1 Ecosystèmes et Ressources Aquatiques, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Tunis, Tunisie. Email: [email protected] (6) UMR 6539 LEMAR CNRS/UBO/IRD/IFREMER, Institut Universitaire Européen de la Mer, Technopôle Brest- Iroise, Rue Dumont d'Urville, 29280 Plouzané, France. Email: [email protected] Abstract The Gulf of Gabes is considered as one of the most productive areas of the southern Mediterranean Sea and it plays an important role in Tunisian economy. It is known to be an archetypal ecosystem in which the effects of fisheries are the most pronounced and it is highly exploited. Thereupon, it becomes necessary to establish some adequate measures in order to facilitate the recovery of the marine resources. The most important sets of these measures are the temporal trawl nets closures and the establishment of Marine Protected Areas. However, these management plans should be assessed beforehand, in a way to make sure of the relevance of the measure put in place and its impact on marine resources. Indeed, modeling may significantly enhance our understanding of the likely impacts of fisheries management plans on groups that are very difficult to study and this approach gives some useful insights at larger spatial scales. We used Ecospace to investigate the potential impacts of several spatial and temporal management scenarios on the ecosystem functioning of the exploited continental shelf of the Gulf of Gabes. The Ecospace model is based on the existing Ecopath model elaborated by Hattab (2013) which includes 41 functional groups and 6 fisheries. In the present study, we simulated several scenarios over a 15-year period, between 1995 and 2010. The management scenarios are divided into two principal sets of fishing restrictions, marine protected areas establishment and the implementation of biological rest-periods. The results show that under the actual fishing situation, exploited resources will remain depleted. In fact based on the outcomes of the simulations, we can approve that fisheries management plans could have a positive impact on several commercial species and could be extremely effective in improving the current situation of marine resources. Indeed, the biomass of several functional groups showed a significant increase. However, that was not always the case, because the biomass of other groups showed a decrease, which can be explained by the trophic cascade. Moreover, we noticed positive effects of fishery management plans on the harvested biomass for several groups. 2 Bulletin de l’Institut National des Sciences de la Mer (INSTM Salammbo). Numéro Spécial (18) : Actes du IXème Congrès Maghrébin des Sciences de la Mer Sousse : 2014 Résumé Face aux nombreuses perturbations engendrées par divers menaces sur les écosystèmes marins, plusieurs stratégies de gestion ont été mises en place afin de remédier à ce problème. Le Golfe de Gabès fait partie des écosystèmes les plus productifs du bassin méditerranéen. C’est un écosystème archétypale au sein duquel se retrouvent de nombreuses perturbations, telles que la surexploitation, la pollution et les invasions des espèces exotiques. Combinés ces enjeux font du Golfe de Gabès un centre d'intérêt pour une étude écosystémique dont la finalité est la gestion durable des ressources halieutiques. Parmi les outils de restauration les plus appropriés pour la conservation des ressources, l'établissement d’Aires Marines Protégées (AMP) et l'instauration des périodes de repos biologique sont parmi les plus utilisées. Néanmoins, il devient nécessaire de s'assurer de l'efficacité de ces mesures avant de les appliquer. L’intérêt de ce travail est d’analyser la réponse de l’écosystème face à d’éventuelles mesures d’aménagement grâce à un modèle Ecospace. Ce modèle a été développé sur la base du modèle Ecopath du Golfe de Gabès, élaboré auparavant par Hattab et al. (2013), comportant 41 groupes fonctionnels et 6 pêcheries. Ce modèle permet de spatialiser les flux trophique d'Ecopath et la dynamique temporelle d'Ecosim. Suite à la simulation sur 15 ans, de scénarios mettant en œuvre diverses mesures de gestion, les AMP et les périodes de repos biologique ont un effet positif sur plusieurs groupes d'espèces prédatrices, qui augmentent leur biomasse. Par contre ceci n'est pas toujours le cas, puisque d'autres groupes subissent une diminution de biomasse expliquée par la cascade trophique. ملخص تتع ّرض اﻷنظمة البحريّة المتواجدة في البحر اﻷبيض المتوسط لضغوط متزايدة من مجموعة متنوعة من التهديدات. من أجل معالجة هذه اﻻضطرابات يمكن إتّباع العديد من اﻻستراتيجيات ﻹدارة قطاع صيد اﻷسماك. يكمن الهدف الرئيسي وراء هذه الدراسة في اكتشاف حلول بديلة تم ّكن من التوفيق بين اﻻستغﻻل المستدام للموارد البحرية و المحافظة على الثروة البحرية في خليج ڨابس. ولقد ت ّمت هذه الدراسة ضمن المنهجية اﻹيكولوجية في الصيد البحري. يعتبر إنشاء المحم ّيات البحرية و مواسم الراحة البيولوجيّة من أكثر اﻹستراتيجيات المتّبعة للحفاظ على اﻷنظمة اﻻيكولوجية ولكن النتائج ليست دائما متو ّقعة. لذلك تر ّكز هذه الدراسة على تقييم استراتيجيّات مختلفة ﻹنشاء العديد من المحميّات البحريّة وفترات مختلفة للراحة البيولوجيّة التي تستهدف الص ْيد القاعي. قمنا بإنجاز نموذج “Ecospace” على مدة 15 سنة )1995-2010) باﻻعتماد على نموذج “Ecopath” المبرمج سابقا. و من ث ّم قمنا بتجربة 8 خطط مختلفة ﻹدارة الصيد البحري ال ّلتي م ّكنتنا من استخراج العديد من المعلومات حول وفرة الموارد البحرية و الكميّات المصطادة. و لقد أظهرت النتائج أ ّن اﻻستغﻻل الحالي للموارد البحرية سوف يتسبّب في تقلص اﻹنتاج البحري كما ا ّنه يمكن ان نعتبر جميع اﻹستراتيجيات المقترحة ف ّعالة من أجل تحسين الحالة الراهنة للموارد البحرية وذلك بنسب متفاوتة. INTRODUCTION For a long time, fishing has been considered as an ancestral activity in Tunisia, and it plays an important role in the economy of the country. However, all the benefits of this activity come with equally high risks of ecological deterioration through over-fishing and habitat destruction (Pauly et al., 2002). The Gulf of Gabes is one of the most productive areas of the Mediterranean Sea (Papaconstantinou and Farrugio, 2000), this ecosystem is considered to be an archetypal Mediterranean ecosystem, in which the effects of fisheries are the most pronounced. That being said, it becomes necessary to establish adequate management measures to help improving the recovery process of marine resources, and the most important sets of these measures are the establishment of Marine Protected Areas (MPA) which are spatial closures (Demestre, 2008), and the biological rest-period which is a temporal benthic trawl nets closures. In the present study, we tried to assess the impact of the implementation of several management plans and for that modeling seems to be a relevant tool to help making sure of the effectiveness of the decisions undertaken. For that end, we used Ecospace model, which integrates the trophic and temporal dynamics of Ecopath and 3 Bulletin de l’Institut National des Sciences de la Mer (INSTM Salammbo). Numéro Spécial (18) : Actes du IXème Congrès Maghrébin des Sciences de la Mer Sousse : 2014 Ecosim and project both over a two-dimension spatial grid with equally-sized homogenous cells, allowing the user to simulate different spatial and temporal management scenarios. MATERIALS AND METHODS STUDY AREA The Gulf of Gabes is located on Tunisia’s east coast and it covers a wide continental shelf area with 35900 km². It extends from Ras Kapudia north, to the Tunisian-Libyan border south, including the islands of Kerkennah and Djerba and the Boughrara lagoon and El Biban. As one of the most productive areas of the Mediterranean Sea, the gulf is also one of the major fishing grounds in Tunisia; therefore, several signs of habitats deterioration were observed due to human activities and pressures (RAC/SPA, 2002). In this study, the area between the isobaths 0 and 20 m were excluded, because of the lack of reliable data. Figure 1: The study area,(Hattab, 2013) ECOLOGICAL MODELING In order to implement an Ecospace model for the Gulf of Gabes, we used the Ecopath model for that region, previously elaborated by Hattab et al. (2013), which creates a static mass-balanced snapshot of energy flows through an ecosystem that is divided up into many functional groups (Christensen and Pauly, 1992), and we also used the Ecosim model developed by Halouani et al. (2013), which allows time dynamic simulations of the relationship of the functional groups (Walters, 1997).