Introduction and extinction of brown trout (Salmo trutta L.) in an impoverished subantarctic stream
- Cooper, J, Crafford, J E, Hecht, Thomas
- Authors: Cooper, J , Crafford, J E , Hecht, Thomas
- Date: 1992
- Subjects: Anadromous fishes -- Marion Island
- Language: English
- Type: Article
- Identifier: vital:6767 , http://hdl.handle.net/10962/d1008044
- Description: Brown trout were introduced to the Van den Boogaard River on subantarctic Marion Island in 1964, and a small population became established. The last individual was seen in 1984, and the species is now considered to be extinct on the island. Their diet was exclusively allochthonous, with snails and spiders predominating. Ages estimated at six to eleven years showed that spawning must have occurred since the original introduction. Since the Van den Boogaard River enters the sea via a waterfall, it is postulated that trout were not able to practice an anadromous life-style, and that this, as well as other factors connected with the impoverished nature of the stream, led to dwarfing of the resident population. No further introductions of alien fish to Marion Island should be contemplated.
- Full Text:
- Date Issued: 1992
- Authors: Cooper, J , Crafford, J E , Hecht, Thomas
- Date: 1992
- Subjects: Anadromous fishes -- Marion Island
- Language: English
- Type: Article
- Identifier: vital:6767 , http://hdl.handle.net/10962/d1008044
- Description: Brown trout were introduced to the Van den Boogaard River on subantarctic Marion Island in 1964, and a small population became established. The last individual was seen in 1984, and the species is now considered to be extinct on the island. Their diet was exclusively allochthonous, with snails and spiders predominating. Ages estimated at six to eleven years showed that spawning must have occurred since the original introduction. Since the Van den Boogaard River enters the sea via a waterfall, it is postulated that trout were not able to practice an anadromous life-style, and that this, as well as other factors connected with the impoverished nature of the stream, led to dwarfing of the resident population. No further introductions of alien fish to Marion Island should be contemplated.
- Full Text:
- Date Issued: 1992
Turbidity-induced changes in feeding strategies of fish in estuaries
- Hecht, Thomas, Van der Lingen, C D
- Authors: Hecht, Thomas , Van der Lingen, C D
- Date: 1992
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446960 , vital:74573 , https://hdl.handle.net/10520/AJA00445096_644
- Description: The aim of this study was to determine the effect of turbidity on the feeding strategies of fish in estuaries. Three species representing different feeding guilds were selected for the investigation. These were Elops machnata (representative piscivore), Pomadasys commefsonnii (a macrobenthivore) and Athefina breviceps (a planktivore). The stomach contents of these fish were examined from a clear and a turbid estuary and some experimental work was carried out on A. brevic8ps to test the hypothesis that turbidity affects feeding behaviour. Turbidity was found to have no effect on size selection of prey, but feeding rate, particularly of visual predators, was reduced at higher turbidity levels. This was caused by a decrease in the reactive distance of the fish. It would appear that in order to optimize the aquisition of food under different turbidity conditions fishes have the ability to change their feeding strategies. Visual predators are more affected by turbidity than are macrobenthic feeders.
- Full Text:
- Date Issued: 1992
- Authors: Hecht, Thomas , Van der Lingen, C D
- Date: 1992
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446960 , vital:74573 , https://hdl.handle.net/10520/AJA00445096_644
- Description: The aim of this study was to determine the effect of turbidity on the feeding strategies of fish in estuaries. Three species representing different feeding guilds were selected for the investigation. These were Elops machnata (representative piscivore), Pomadasys commefsonnii (a macrobenthivore) and Athefina breviceps (a planktivore). The stomach contents of these fish were examined from a clear and a turbid estuary and some experimental work was carried out on A. brevic8ps to test the hypothesis that turbidity affects feeding behaviour. Turbidity was found to have no effect on size selection of prey, but feeding rate, particularly of visual predators, was reduced at higher turbidity levels. This was caused by a decrease in the reactive distance of the fish. It would appear that in order to optimize the aquisition of food under different turbidity conditions fishes have the ability to change their feeding strategies. Visual predators are more affected by turbidity than are macrobenthic feeders.
- Full Text:
- Date Issued: 1992
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