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Effect of salinity and environmental changes on the fish community of the St Lucia Estuarine System with focus on the salinity tolerance of Oreochromis mossambicus (Mozambique Tilapia)

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dc.contributor.advisor Vivier, L.
dc.contributor.advisor Cyrus, D.P.
dc.contributor.author Schutte, Quintin
dc.date.accessioned 2015-11-10T12:31:14Z
dc.date.available 2015-11-10T12:31:14Z
dc.date.issued 2014
dc.identifier.uri http://hdl.handle.net/10530/1409
dc.description A thesis submitted to the Faculty of Science and Agriculture in fulfilment of the requirements for the Degree of Master of Science in the Department of Zoology at the University of Zululand, South Africa, 2014 en_US
dc.description.abstract St Lucia, the largest estuarine lake system in Africa, has been closed since 2002, except for a brief opening in 2007 caused by Cyclone Gamede. Mouth opening in 2007 was preceded by five years of low lake levels and hypersaline conditions which greatly reduced marine fish species diversity. Regardless of this, the freshwater tilapia, Oreochromis mossambicus has been found in abundance in all parts of the system. This indicates that O. mossambicus is capable of surviving hypersaline conditions when no other fish species can. Mouth opening in 2007 caused the system to partially fill marine salinities were restored and also allowed for recruitment of marine species back into the system. Following re-closure in August 2007, salinities in North Lake became hypersaline during 2009-2010. In 2012, a “beach channel” was dug to re-connect the St Lucia Narrows to the Mfolozi-Msunduzi Estuary, allowing water to enter the system and provide access to the ocean for recruitment of marine species. The study investigated the effect of salinity and environmental changes on the fish community structure of the St Lucia system during periods of mouth closure as well as after opening of the new beach channels connecting St Lucia to the Mfolozi system.Sampling was conducted from May 2008-Nov 2014 at six sites in the St Lucia system using small (10m) and large (70m) seine nets and CPUE’s were calculated for each site as the number of fish caught per meter of net, per haul. Fish were identified measured and returned to the system. The salinity tolerance of O. mossambicus from St. Lucia was also investigated under laboratory conditions. Acclimation of O. mossambicus was done at salinity intervals of five with a 96 hour exposure trial to test for survival. Spatial changes in the fish community were driven by the salinity gradient across the system, while temporal changes coincided with major changes in the salinity state of the system. Marine species dominated in terms of species number but freshwater and estuarine species dominated the fish abundance, notably O.mossambicus and Ambassis ambassis. Prior to opening of the beach channel, the number of species decreased from 51 in 2008 to 37 in 2011. The abundance of marine species decreased by >75%as the system became progressively more hypersaline and the closed mouth limited recruitment. Opening of the beach channel caused a decline in salinities and allowed for 12 marine species top re-enter the system in limited numbers. Oreochromis mossambicus was the most abundant species in the system, accounting for 48.8% of the catch between 200-2014 and dominating the fish assemblage in salinities between 30-90 (highest recorded salinity). Estuarine species were dominant in salinities between 0-20, while marine species dominated the fish assemblage in salinities between 20-30. In the laboratory, the salinity tolerance of O.mossambicus was found to be 0-105, with >70% survival in 105. Freshwater deprivation and mouth closure had the biggest impact on the fish assemblage and a regular more extensive connection to the ocean is therefore, needed to maintain healthy fish populations in Lake St Lucia and off-shore marine populations. en_US
dc.language.iso en en_US
dc.publisher University of Zululand en_US
dc.subject Oreochromis mossambicus --fish assemblage --drought --hypersalinity --recruitment --mouth closure --St Lucia --estuary en_US
dc.title Effect of salinity and environmental changes on the fish community of the St Lucia Estuarine System with focus on the salinity tolerance of Oreochromis mossambicus (Mozambique Tilapia) en_US
dc.type Thesis en_US

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