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Distribution patterns of the striped mullet (Mugil cephalus) in mangrove creeks of Zanzibar, Tanzania
Stockholm University, Faculty of Science, Department of Zoology. (Ecology)
Fisheries and Aquculture. (Fisheries Biology)
Stockholm University, Faculty of Science, Department of Zoology. (Ecology)
International Environment and Development Studies.
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(English)Manuscript (Other academic)
Abstract [en]

Spatial and seasonal variations in density of the striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar (Tanzania) during a one-year cycle. Fish were collected monthly in the lower, intermediate and upper reaches of each creek using a beach seine net (each haul covering 170 m2). All individuals collected were juveniles with a mean size of 2 to 16 cm (standard length). The density of juvenile mullets inhabiting mangrove creeks differed significantly among the different creeks, but the patterns within creeks were consistent, with higher densities upstream in three of the creeks. In general, small-sized juvenile mullets (2-10 cm) were more abundant in the upper reaches compared to the lower and intermediate sites in most creeks. Seasonal patterns were fairly weak, although high mullet densities were observed during the period of heavy rains (from March to May). Principal component analysis (PCA) showed that a muddy bottom with microphytobenthos was likely important to explain high mullet densities, although site-specific variables like low water depth and water clarity may also be important. Our findings suggest that the densities of juvenile striped mullet vary among sites and creeks in response to refuge availability from turbid shallow waters and the accessibility of food resources from benthic microalgae.

Keyword [en]
Mugil cephalus, Population density, Marine embayment, Spatial and seasonal variation, Zanzibar Island
National Category
Fish and Aquacultural Science
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-27396OAI: oai:DiVA.org:su-27396DiVA: diva2:214032
Available from: 2009-05-01 Created: 2009-05-01 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Fish community patterns in Tanzanian mangrove creeks
Open this publication in new window or tab >>Fish community patterns in Tanzanian mangrove creeks
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human beings have exploited the biota of mangrove systems for centuries and fish continue to be one of the main products harvested from these habitats. The assumption of mangroves functioning as recruitment areas for juvenile fish from neighbouring habitats such as seagrass beds and coral reefs is a common argument for conservation and management of mangrove ecosystems. Yet, mangrove systems are increasingly in decline worldwide primarily because of destructive anthropogenic activities. In the present thesis, fish assemblages in various mangrove creeks in Tanzania were investigated. Specifically, it dealt with the distribution, abundance and trophic structure of fishes in space and time as predicted by habitat characteristics and environmental conditions occurring naturally and following human-induced changes of clearing for construction of ponds for salt production and fish farming. In addition, the variation in population density and genetic connectivity of the economically important striped mullet (Mugil cephalus) was examined. In undisturbed creeks the fish abundance and assemblage composition showed inconsistent spatial patterns within and among different creeks that appear to be strongly influenced by species-specific responses to dominant bottom substrate types and to some extent to water depth and clarity. Seasonality had little impact on most fish assemblage variables. The genetic analysis showed mixed demes of Mugil cephalus and significant separation between Zanzibar Island and Tanzania mainland. Anthropogenic effects were found on the structural and functional organisation of fish assemblages resulting in lower densities, species numbers, diversity and number of trophic groups in the reservoirs compared to less disturbed sites. These changes in fish assemblage composition seem to be caused by an increase in salinity and water temperature as well as by the loss of refuge and feeding grounds. The findings in this thesis will contribute to coastal management planning for conservation and suggests integration of various activities (like fish farming and salt production) in order to maximise the economical use of deforested areas.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2009. 38 p.
Keyword
Mangrove ecosystems, fish assemblages, Mugil cephalus, population genetics, spatial and seasonal variability, human disturbance, East Africa
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-27168 (URN)978-91-7155-879-4 (ISBN)
Public defence
2009-05-27, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-06 Created: 2009-04-23 Last updated: 2009-05-05Bibliographically approved

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