Recruitment of juvenile marine fishes into permanently open and seasonally open estuarine systems on the southern coast of South Africa
- Authors: Whitfield, Alan K , Kok, H M
- Date: 1992
- Subjects: Marine fishes -- Migration -- South Africa , Estuarine fisheries
- Language: English
- Type: Text
- Identifier: vital:15020 , http://hdl.handle.net/10962/d1019801 , ISBN 0-86810-232-6 , Ichthyological Bulletin of the J.L.B. Smith Institute of Ichthyology; No. 57
- Description: The recruitment of juvenile marine fishes into the Knysna and Swartvlei estuaries was monitored over 30 months using seine, scoop and cast nets. The relative abundance, seasonality and growth of the dominant species are presented, and includes the Cape stumpnose Rhabdosargus holubi, white steenbras Lithognathus lithognathus, blacktail Diplodus sargus, strepie Sarpa salpa, Cape moony Monodactylus falciformis, southern mullet Liza richardsonii, groovy mullet Liza dumerilii, striped mullet Liza tricuspidens, flathead mullet Mugil cephalus, freshwater mullet Myxus capensis and leervis Lichia amia. Information on a further 12 species is also provided. Recruitment of most fish species into the Swartvlei and Knysna estuaries reaches a peak during summer, which coincides with maximum food resource availability and corresponds to the time when systems along this section of the coast are often open to the sea. Artificial winter breaching of the Swartvlei mouth has occurred in the past, and has generally led to the premature closure of the system and loss of the ‘head’ of water needed for the summer opening. This type of mouth manipulation leads to reduced availability of estuarine nursery areas for marine fishes along the southern Cape coast. Comparisons between the recruitment of juvenile fishes into the Knysna and Swartvlei estuaries indicate that higher densities of most species were recorded in the former system. This is attributed mainly to the fact that the Knysna mouth is deep, permanently open, and has a strong marine influence when compared to the shallow, narrow and seasonally closed Swartvlei mouth. However, in a regional context both Knysna and Swartvlei are large, unpolluted systems, which serve as important nursery areas for many species of fish. On this basis alone, these contrasting estuarine systems should be allocated the highest possible conservation status. , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 1992
- Authors: Whitfield, Alan K , Kok, H M
- Date: 1992
- Subjects: Marine fishes -- Migration -- South Africa , Estuarine fisheries
- Language: English
- Type: Text
- Identifier: vital:15020 , http://hdl.handle.net/10962/d1019801 , ISBN 0-86810-232-6 , Ichthyological Bulletin of the J.L.B. Smith Institute of Ichthyology; No. 57
- Description: The recruitment of juvenile marine fishes into the Knysna and Swartvlei estuaries was monitored over 30 months using seine, scoop and cast nets. The relative abundance, seasonality and growth of the dominant species are presented, and includes the Cape stumpnose Rhabdosargus holubi, white steenbras Lithognathus lithognathus, blacktail Diplodus sargus, strepie Sarpa salpa, Cape moony Monodactylus falciformis, southern mullet Liza richardsonii, groovy mullet Liza dumerilii, striped mullet Liza tricuspidens, flathead mullet Mugil cephalus, freshwater mullet Myxus capensis and leervis Lichia amia. Information on a further 12 species is also provided. Recruitment of most fish species into the Swartvlei and Knysna estuaries reaches a peak during summer, which coincides with maximum food resource availability and corresponds to the time when systems along this section of the coast are often open to the sea. Artificial winter breaching of the Swartvlei mouth has occurred in the past, and has generally led to the premature closure of the system and loss of the ‘head’ of water needed for the summer opening. This type of mouth manipulation leads to reduced availability of estuarine nursery areas for marine fishes along the southern Cape coast. Comparisons between the recruitment of juvenile fishes into the Knysna and Swartvlei estuaries indicate that higher densities of most species were recorded in the former system. This is attributed mainly to the fact that the Knysna mouth is deep, permanently open, and has a strong marine influence when compared to the shallow, narrow and seasonally closed Swartvlei mouth. However, in a regional context both Knysna and Swartvlei are large, unpolluted systems, which serve as important nursery areas for many species of fish. On this basis alone, these contrasting estuarine systems should be allocated the highest possible conservation status. , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 1992
The Benthic invertebrate community of a Southern Cape estuary : structure and possible food sources
- Authors: Whitfield, Alan K
- Date: 1989
- Language: English
- Type: text , Article
- Identifier: vital:7154 , http://hdl.handle.net/10962/d1011871
- Description: Cluster analysis of invertebrate communities in the Swartvlei estuary revealed that vegetated (Zostera capensis) sites were distinct from unvegetated ones. `Indicator species' for the eelgrass group included Melita zeylinaca, Loripes clausus, Natica tecta and Palaemon pacificus, whereas those for the bare sand community were Urothoe pulchella, Callianassa kraussi, Iphinoe truncata and Pontogeloides latipes. Infaunal bivalves comprised >60 % of the invertebrate biomass at Zostera sites but <5 % at bare sand sites. Conversely the infaunal anomuran C. kraussi dominated the sandy sites (>80 %) and was a minor component (<5 %) at eelgrass sites. The supratidal invertebrate community was dominated by Orchestia spp. which live and feed on wrack detritus. Litterbag experiments revealed that degradation of Zostera leaf wrack was rapid during the first thirty days after deposition but slow between 40 and 140 days. Laboratory experiments indicated that Orchestia consumption of wrack material could not account for the rapid weight loss recorded in the natural environment. Preliminary diet analyses of intertidal and infratidal zoobenthos revealed that most invertebrate species feed on detritus and associated microorganisms. Filamentous algae and diatoms dominated the gut contents of only three out of 18 macrobenthic species, and living Zostera was not an important food item for any invertebrate examined.
- Full Text: false
- Date Issued: 1989
- Authors: Whitfield, Alan K
- Date: 1989
- Language: English
- Type: text , Article
- Identifier: vital:7154 , http://hdl.handle.net/10962/d1011871
- Description: Cluster analysis of invertebrate communities in the Swartvlei estuary revealed that vegetated (Zostera capensis) sites were distinct from unvegetated ones. `Indicator species' for the eelgrass group included Melita zeylinaca, Loripes clausus, Natica tecta and Palaemon pacificus, whereas those for the bare sand community were Urothoe pulchella, Callianassa kraussi, Iphinoe truncata and Pontogeloides latipes. Infaunal bivalves comprised >60 % of the invertebrate biomass at Zostera sites but <5 % at bare sand sites. Conversely the infaunal anomuran C. kraussi dominated the sandy sites (>80 %) and was a minor component (<5 %) at eelgrass sites. The supratidal invertebrate community was dominated by Orchestia spp. which live and feed on wrack detritus. Litterbag experiments revealed that degradation of Zostera leaf wrack was rapid during the first thirty days after deposition but slow between 40 and 140 days. Laboratory experiments indicated that Orchestia consumption of wrack material could not account for the rapid weight loss recorded in the natural environment. Preliminary diet analyses of intertidal and infratidal zoobenthos revealed that most invertebrate species feed on detritus and associated microorganisms. Filamentous algae and diatoms dominated the gut contents of only three out of 18 macrobenthic species, and living Zostera was not an important food item for any invertebrate examined.
- Full Text: false
- Date Issued: 1989