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The fish community of the Berg River estuary and an assessment of the likely effects of reduced freshwater inflows

Keywords: fish community , Berg River , estuary , freshwater inflows , Liza richardsonii , freshwater species , Caffrogobius nudiceps , marine biogeographical , west coast estuaries , freshwater inflows , Atherina breviceps , Gilchristella estuaria , distributed species

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ENGLISH ABSTRACT: Data concerning the species composition, abundance and distribution of fishes in habiting the Berg River estuary are presented and used to assess the value of the estuary to fish, and the likely effects of reduced freshwater in flows. A total of 31 species was recorded, eight of which were classified as estuarine residents, 11 as marine estuarine-opportunist, six as marine stragglers and six were freshwater species. Liza richardsonii, an opportunist, was the most abundant (54% N) and widely distributed species encountered during the winter and summer seine-net surveys. Three other species (all residents) contributed more than 10% of the total catch; Atherina breviceps and Caffrogobius nudiceps occurring most abundantly in the lower estuary, and Gilchristella estuaria in the middle estuary. The low number of species compared with estuaries in other regions of the South African coast reflect a well-established marine biogeographical trend. The higher proportions of resident species, entirely dependent species and partially dependent species suggest, however, that west coast estuaries may be more important to the fish that inhabit them than are estuaries in other regions. It is concluded that the fish community of the estuary is already suffering the effects of habitat degradation and that further reducation in freshwater inflows are not desirable. ******** AFRIKAANSE OPSOMMING: Data betreffende die spesiessamestelling, talrykheid en verspreiding van visse wat die Bergriviermond bewoon, word aangebied en gebruik in 'n raming van die waarde van die mond vir die bewonende visse, en die moontlike gevolge van verminderde varswaterinvloei. 'n Totaal van 31 spesies is aangeteken, agt waarvan geklassiliseer is as mondinwoners, 11 as mariene trekvisse, ses as mariene swerwers en ses as varswateisoorte. Liza richardsonii, 'n trekvis, was die volopste (54%N ) en mees wydverspreide spesies wat te gekom is gedurende die winter- en someropnames. Die ander spesies (almal inwoners) het meer as 10% bygedra tot die totale vangs, met Atherina breviceps en Caffrogobius nudiceps wat volopste in die laer-, en Gilchristella estuaria in die middelgedeeltes van die strandmeer, voorkom. Die klein aantal spesies weerspie l 'n goed vasgelegde mariene biogeografiese neiging. Die groter proporsie van inwonerspesies, total afhanklike en gedeeltelik afhanklike spesies suggereer egter dat Weskusriviermonde belangrikerr mag wees vir die visse wat hulle bewoon as riviermonde in ander streke. Die gevolgtrekking word gemaak dat die visgemeenskap van die riviermonde reeds on

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