Introduction and extinction of brown trout (Salmo trutta L.) in an impoverished subantarctic stream
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.(Received August 8 1990)
(Accepted June 3 1991)
Key Words: anadromy; diet; fish; growth; life-history style; Marion Island.
p1 Department of Zoology, University of Venda, Pvt Bag X2220, Sibasa, Venda, southern Africa