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  • 1
    Publication Date: 2021-05-19
    Description: The pearl oyster Pinctada radiata and the cockle Cerastoderma glaucum are among the most abundant bivalve molluscs in southern Tunisian waters. These species are not currently subject to any investigation despite their important economic value in the world. For this reason, their biological parameters, their spatial distribution and their stock assessment were undertaken in the Gulf of Gabes. The reproductive cycle was studied in relation to variations of the environment parameters. The specimens were collected monthly during one year (2007) in sites of El Kraten and El Jorf (Kerkennah Islands) for the first species and sites of Sidi Mansour and El Hicha (North of Sfax and Gabes) for the second. An intraspecific polymorphism biometric trait for P. radiata and C. glaucum was performed using statistical comparison methods and multivariate analysis methods. Results of analyzes showed heterogeneity between populations. For Pinctada radiata, the sex ratio unbalanced, although males dominated among smaller individuals and females were predominant in larger size-classes. Evidence of protrandric hermaphroditism was observed with males maturing earlier than females. Seasonal changes in macroand microscopic properties of the gonads of both sexes showed that this species displayed a clearly defined annual reproductive cycle with a major peak in summer and a minor peak in autumn. The onset of reproduction appears to be triggered by the rising seawater temperature during spring and summer. P. radiata exhibited a short resting phase that occurred simultaneously in both sexes from the end of December until early February. For Cerastoderma glaucum, the overall samples presented a balanced sex ratio, with males dominating among smaller individuals and females predominating in larger size classes. The seasonal changes assessed through macro- and microscopic properties in the gonads of both sexes indicated a clearly defined annual reproductive cycle. Reproductive activity of C. glaucum was greatest from spring to late autumn, with two reproductive peaks (May and November). Gametogenic activity in both sexes was apparently triggered by the rising seawater temperature during spring and summer. These results support previous findings of latitudinal changes in the reproductive behaviour of C. glaucum. Due to the extensive period of gonadal activity, C. glaucum exhibited a short resting phase that occurred simultaneously in both sexes throughout January and February. In terms of stock assessment and spatial distribution of P. radiata, results showed a scattered distribution pattern of the species according to location and depth ranging between 0 and 145 ind.m-². P. radiata was encountered from the intertidal zone to 40 m depth, with a highest population densities recorded at depth range of 2-20 m. The total stock was estimated to be 27584.9 ± 11504.5 million individuals. Oyster distribution seems influenced by the substrate type. This high population of pearl oysters was associated with large cover of seagrass Posidonia oceanica which provides an excellent substratum for attachment. The littoral zone seems not to be the preferred habitat for the proliferation of this immigrant species. Oysters’ size increased steadily with depth, ranging from a mean of 37.98 ± 0.40 mm SH at 0-1 m to 60.98 ± 0.68 mm SH at 20-100 m depth range. Size structure analysis showed that deep water population was dominated by large individuals reaching 96 mm SH. In terms of geographical occupation and stock assessment of C. glaucum, results showed a scattered distribution pattern of the species according to location. The consequence was a remarkable biomass which represented 4736 tons of total fresh weight and high abundance levels reaching over 1982 million individuals estimated in the area of 20122 hectares. In conclusion, this study is the first report of an extraordinary abundance of Pinctada radiata and Cerastoderma glaucum in southern Tunisian waters. It gives more information about their stocks in the colonization area. The data may help to determine future quantitative changes indicating trends in the study area that are exposed to various factors of environmental conditions and human activities.
    Description: Submitted
    Description: ABONDANCE
    Description: BILOGIE
    Description: Pinctada radiata
    Description: Cerastoderma glaucum
    Description: Huitre perlière
    Keywords: Abundance ; Biology ; Shellfish
    Repository Name: AquaDocs
    Type: Theses and Dissertations , Phd thesis
    Format: 170
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  • 2
    Publication Date: 2021-01-30
    Description: The first meeting of the South West Indian Ocean EAF Regional Task Group (RTG) was held in Mombasa, Kenya, from 27 to 30 January 2009, together with an ecological risk assessment methodology workshop. It was attended by 20 partic ipants from the South West Indian Ocean (SWIO) countries, the South West Indian Ocean Fisheries Project (SWIOFP), the Agulhas and Somali Currents Large Marine Ecosystems (ASCLME) project, the Scientific Committee of the South West Indian Ocean Fisheries Commission, the United Nations Environment Programme (UNEP)/Nairobi Convention Implementation Unit, the African Union Commission and FAO. The RTG is an implementation structure under the EAF-Nansen project GCP/INT/003/NOR and serves as the forum for training in ecological risk assessment that is the methodology used for the identification and prioritization of issues requiring management attention. The main objectives of the meeting and workshop we re to discuss and facilitate key processes and activities for the implementation of the ecosystem approach to fisheries management in the South West Indian Ocean region including the modalities for the formation and functioning of the RTG and National Task Groups (NTGs). It was explained that, to be able to achieve the objectives of implementing an ecosystem approach to fisheries at the national level, certain key structures have to be in place including the NTG with representatives of key stakeholders in a given fishery and that would take the lead in the process. An overview of the key concepts and process of the ecological risk assessment methodology were clarified. Participants were also introduced to the preparation of EAF baseline reports to be used as initial input for the work on ecosystems approach to fisheries. It was explained that the preparation of the report is to be led by national and regional experts and overseen by the NTG. For the exercises the participants worked in three subgroups formed during the meeting with each group selecting a chairman who moderate d the discussions and a rapporteur. The participants expressed satisfaction with the development of a communication strategy for the project and especially with the participatory approach used.
    Description: FAO, NORAD, Institute of Marine Research
    Description: Published
    Description: National task groups
    Description: Regional task groups
    Description: Ecosystem Approach to Fisheries
    Keywords: Ecosystems ; Fisheries ; Ecosystems ; Fishery resources ; Fisheries management
    Repository Name: AquaDocs
    Type: Report , Non-Refereed
    Format: 36
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  • 3
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    Nigerian Institute for Oceanography and Marine Research | Lagos, Nigeria
    Publication Date: 2021-01-30
    Description: Published
    Description: Fisheries newsletter
    Keywords: Fisheries ; Marine sciences ; Fisheries literature
    Repository Name: AquaDocs
    Type: Report , Non-Refereed
    Format: 30pp.
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  • 4
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    Nigerian Institute for Oceanography and Marine Research | Lagos, Nigeria
    Publication Date: 2021-01-30
    Description: Published
    Description: Fisheries newsletter
    Keywords: Fisheries ; Marine sciences ; Fisheries literature
    Repository Name: AquaDocs
    Type: Report , Non-Refereed
    Format: 34pp.
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  • 5
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    Nigerian Institute for Oceanography and Marine Research | Lagos, Nigeria,
    Publication Date: 2021-01-30
    Description: Published
    Description: Fisheries newsletter
    Keywords: Fisheries ; Fisheries literature
    Repository Name: AquaDocs
    Type: Report , Non-Refereed
    Format: 11pp.
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  • 6
    Publication Date: 2021-05-19
    Description: Instittuto Nacional de Investigaçao Pesqueira, INIP, luanda , Angola
    Description: Bachelors
    Description: Trabaho de fin cdoursado para obtençâo do grau de licenciatura em Biologica
    Description: Published
    Description: biologia marinha, fitoplâncton, limnologia, algas
    Description: marine biology, phytoplankton, algae,
    Keywords: Phytoplankton ; Nannoplankton ; Biology ; Limnology ; Algae
    Repository Name: AquaDocs
    Type: Theses and Dissertations , Bachelor thesis
    Format: 56
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  • 7
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    Nigerian Institute for Oceanography and Marine Research, | Lagos, Nigeria,
    Publication Date: 2021-01-30
    Description: Published
    Description: Fisheries newsletter
    Keywords: Fisheries ; Fisheries literature
    Repository Name: AquaDocs
    Type: Report , Non-Refereed
    Format: 8pp.
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