The importance of estuary head waters as nursery areas for young estuary- and marine-spawned fishes in temperate South Africa

The restriction of freshwater flow into estuaries, the presence of in-stream barriers and the occurrence of invasive fish species in these habitats are identified as major threats to these young estuary- and marine-spawned fish species. These aspects have been investigated using the distribution and abundance of young estuary- and marine-spawned fish species in the headwater environments of four permanently open estuaries of the Eastern Cape, South Africa. Fishes were collected twice per season over the 2009 and 2010 period, using mixed method sampling with seine net hauls and overnight fyke net deployments. Of the 74,751 fishes collected, 37,444 fishes, 18 families and 34 species were taken in fyke net catches, while 34,308 fishes, 21 families and 38 species were caught in seine nets. In the Great Fish, Kowie, Kariega and Sundays River systems, juveniles of estuarine residents dominated headwater catches, followed by juveniles of estuary-dependent marine species. The prevalence of larval and small juvenile stages of estuary- and marine-spawned fish species highlights the potential importance of these transitional areas for young fish.