Larval fish dynamics in the Nxaxo-Ngqusi Estuary Complex in the warm temperate–subtropical transition zone of South Africa

Abstract

The larval fish assemblage was investigated in the permanently open Nxaxo-Ngqusi Estuary Complex, situated in the subtropical–warm temperate biogeographic boundary zone of South Africa. Larval and early juvenile fishes were collected in summer and winter of 2007 and 2008 using a mixed method approach by boat-based plankton tows in mid-channel waters and seine net hauls along the margins. In total, 20 455 fishes were collected representing 21 families and 40 taxa, of which 13 900 fishes were from mid-channel sites (15 families and 21 taxa). Seine  net hauls along the estuary margins produced 6550 fishes representing 18 families and 33 taxa. Gobiidae was the dominant fish family in the mid-channel waters followed by the Clupeidae whereas the opposite was found in marginal waters. Estuary-resident larvae were the dominant group in the estuary complex. The catches typically reflected a more warm temperate community, although subtropical-associated species were present. Fish density in mid-channel waters was higher in the Ngqusi arm than that of the Nxaxo arm, whereas along the marginal waters, CPUE was higher in the latter. Fish densities in mid-channel waters and CPUE along the margins were typically higher in summer.

African Zoology 45(1): 63–77 (April 2010)